C language for AVR from Atmel AVR Barnet

kiTHö&;äü: Embedded E P=ipgrarnming änd the Atmel Znd Edition AVR Barnett. fox and ü'full Embedded C Prograrnrning and the Atmel AVR znJffi Richard H Bdrnett. Sarah fox and Larrgsöffii Enierlhe word of embeddedprogamfitingand micrccontroler appticalions: Ofe of the oity booksavatabe todäy|ral uses the ncreasngy popLar and cost efiectiveAtmetAVRembeddedconrroter as rhe pa ;m anctappicaton f6r Learnng, Enbedded C Prcgtanrning and the Attnel AVB,2E is lhe perfcct choice ror novces. Fearurng a host oi iLrty iuncr on;l exarnpeappicatons.th s h ghy innovarvebook €nabtesuserslo adopra ,tearnby do ng appioachs ihey deveop the knorvedgeand skls nee.leclto achele profcrency.Fotolvng an inrroduction lo Atme AVR BSC processors,reacters are aunchedirnmadately nlo an embeddedC langLrage lutoriat.Here.they lexperment wth varablesand constants, operalorsand expressons,contro siatemefts.potnlenran{l arays. memorytypes, preprocessor.tir€ctves. reat-Ume n additon to a comprehensive lbraryfunctionsrefere.ce.an entirechapteron theCodevisonAVFC Compierprov.tesc ear, step by step nslructon n DE instalalondd operarion.mixingA€semberwrh C. and usingtire Code Wzard Code Generato.Useoi parpherals slch as keypadsLCDd spays.and othercommonembedd€.] m ciocontrot ef rc arectdevices s aso exporedlLry n th s al-incllslve.siateof the air proqrammeas holv to an.treference manlat. Features: . emphassis paced on embeddedsystemsproglamming. lrirh numerousexarnpes ro ead rea.lersro masreryoJ both beginnng afd advancedtecMques . a backot bookCD conians exampe prcgramsiromthe texl p us Codevison AVR DEand C Comper evatlatiorversons, pfold n9 lserswih eveMhi g theyneedto gel sta.red ' aa'andwrllen exercses . everysectionundersco.e keyconceplswh e offeringa.iclilonaloppoirunit es to apptyembed programming ded applcation technques . handyappefi:lc€sncllde stepby step nsttucrions for geltingstairedwith the Codevson AVFC como er and the Atme STK500, t ps ior writn9 smalercode.and an Asct|labte AbDut the Authors: Dr FlichardH. Barnetthas beeninsltuctifgn lhe a.€ ot embedcted m crocontroers for tfrepaste ghteer r yearsa,jo cur renty consuls activey n ihe ned. P.or to histenrreas a professorof Eleclca Eig neeingTechnoogyat pufdueUniveßity, he spenl len yearsas an engineeri.r tlre aercspaceet€crroncs industry Dr Aameri! rea.hlng awar.J;irc ude rhe Chares B. [rllrpi]yAwardas oneof the bestteachersat PurdueUnivers ty and Purctue Untversity,s Bookoi creat Teacheß,a ist of the 225 mosl nfuenla teachersoverPlrdl]es enlre hisrorv LarryO'Cullreceived a Bachelor of Sc encedegreefromthe SchootoiEteciricat Engineering Techioogyal purdueUniveßry H s previols€xperlence incurlesseveratyears oi ü/orkingin Eedricatan.tSoftwareEngtieerngand Enginee.tng management anddeveopmenlandhe hasbee. sledas invenror,,co patents.He is curientivthepresideniand CEO inve.toron numeroLrs oi Pr o (fomerlyProgress ve BesoLrrces LLC) a companysp.\ ilt zing n m.o\. r vc . orfmercra, ndustna, ana consLmer Salah Cox hasa Bacheor of Sciencedegreei. borhCompurerand Etectricat Engineerng irom plrdue Universry. She is y lhe V ce Presdent ancl D rector or SoftwareDevetopmenrar pr io (formerlyprcgressiveResolrces LLC),wher6 she cL.rnerll hs cleveroped sonwareror projectsrangng fiom smärtconsumer pro.Jucrs ro indusrrarproductsand t€srequjpment. These prqects rravespannedseveralfieds, among lhem autornotive,medical,antertanment,ch t.i .levetoDment, DUbUc satety/edlcal on soundand imagecompression. üd cofslruction.In addirion,\,4s.Cox has be€n sl€rtas oo-nvemoron nunerolspateniapplcalons Also Avdilatrle from Thomson Delmar Lea.nins; 'Order *1-401E 3748 4 ------*-- g d o,öM,o rppl . Bd.r--,Lo\.ao, visit M.d€hanemi.g.com/eleronics ww3lel@ictechron lor your liferong lefling Fd m@ rffing elutions lR-.bmw.drl/lffing by Thom$n: or soknions ilülili lilll ül and the Atmel AVR,2e THOIWSON ___.----*--" DELMAR LEARNING :?rogr,arrming and the Atmel AVR,2e RICHARD BARNETT LARRYO'CULL SARAH COX -rl-lorwsoN _-----*--__ DELMAR LEARNING Enbedded C hosymmirg dd t}le Annel AVR, 2e Richxrd llarnctt, Ldry O'Cr 1,and Sarrh Cox Vi.€ Pr€sid€f,t,T.clnology .nd S€niorProdncion Mmlger: Pmdu.tion Coodin^tor: DirectorofLeuning Solurions: Ma*ctirg Coordimtor: ÄrrlDßi8r Coorilinltor: ScniorAcqtrisitions Dilitor: Scnior Preiluct NLnaScr COPYRICHT O 2007ThonxonDclmxr Leaming,r divisionofTn.nso. Leanl iqj In.. Alltghs r$ndTheTh.mson L.Minglff.l,ogo is a icgni.rcdrade ,nrn(usedherehurdfl licensc. 23,1 5IX06 For noft i. aornation .öntict Tlonso n 5 [4rNeilDiirc, PO Bo] 3007, Clifton P.rl<,hvY 12065 8007 Or Andusor rheWorld $ridc Wcb d rywwddmaneuri.g.corl -AlL RIGH LS RESERVDD.No prit of rhis vorh overd bv thc copyrigntLüeor nxtr bc ftFiodtred nr rnt foin or by ?nt means gri!hi., ele...ri.j or ncdrMi cxl,nrcludingphorocopting,recordinF txting,Webdistibntjon,or infomrtio! noragernd reüievd $,$.nsannou! tbe writcn Fermnsior ol t]| publisher lor pcrmissionto ure m.tcrirl fron tne &f or produd,.onkd usb,1, Tcl. (300)730-2214 Fu (800)t30-2215 rn*{d,onsonrighF.con Lil'rrJy of Cong€$ Crt,IoginS-in EnbeddcdC progannri.g andrhe Abrel AvR/lticl\ird Bxmert, Lu{ ln.ludcs bit liognphiQl reGieftcs ISBN 1 118039594 (rlL.Ftei) 1. c (Conrfti lrosrin hnsrrse) 2. Enbedded comluter sys.hs D6igtr rnd oNnrdion.3. lilsc ni.ropro..soß. L O'Cul1,l-my lI. Cox,S,riL (Sanh,\ßon) TILTirle. c476.73.Cr583782006 20060071i3 NOTICD TO THE RLADDR Publnfier doesnobühnt or gu anre. my ol dr pFdüc6 describcdhcrcin or |erlom art ind.pcndent ?nahsn i, connc tionwith rN ofthc prodüctinfomatlon.ontdncdlerein.Publishddö.snol Numq ander?(sdy dischins,rn].objjgarior to obtin rnd in.lude nformrion dhü dnn thr provi&d b n bt, the manufx.turci The edci is *Freslv nnrned to .onsids ?nd sdotr .11$lcty pftmtrtions tlut miglu b. indiG€d 6j' nE elivirtes hd.in a.d to aroid dl Fotenrirl haz.rds.By folöiiqj tne nrtrudions conlainedherei., rhe nd.r witingl}.Asums ltl rGksir conneclion wnh n'dr in$nciions Tne publi6hermal<€sm rerernrition or rilnxnties of rnv ltind, in.ludnrg bur nor linncd to, tle vrnnties of ntncs fdfrtjünir lu.posc or nerchütüiliqt nor rc ?nv slch €lEsentations inplied tl €sp.rt b thc mterijl serfonh trerd,, md ine publishci nk.s no responsibilir_v{ithrcspectr, suchm.terial. The publishershrll not beti Jtcfor rnl, stecjal,conseqncnnal,or eremplxr! damxgesre lii.g, nr wholc or lxrt, from dr nd.ß sc of, or Elirne uron, tlis ddui3t. 1.10.3Pointersto Structure 1 . 1 0 . 4U n , o n .s. . . . . . . . . . . . . . '-''''''''''..-''''''......'''''',....''''''',,'--''''''''''''57 ..._...........58 viil 4.4 4.1 4.8 4.9 APPENDIX D INSTALLINGAND USINGTHECABLEAVR-.-..,.,.-....,.....475 APPENDIX E THE MEGAAVR-DEVDEVELOPMENTBOARD-.-......-.489 APPENDTXF ASCI T4BLE............... .............................493 APPENDfX G AVR TNSTRUCTTON SET SUMMARY..................................4e7 aPPENDtX H ANS\^/ERSTOSELECTEDEXERCtSES.............................s03 APPENDIX I A'FAST START"TO EMBEDDED c PROGRAMMTNG AND THE 4VR................... _____________-............soe INDEX....-......-.................. .........-..........-..................................... t9 This te,rtis designedboth to teachC languageprogrammingasit appliesto cmbeddcd microcontrollers and to provide knowlcdge in the application of the Atmcl@ family of AVR@ RISC microcontrolleß. I N T C N D E DA U D I E N C E This book is desiEnedto servetwo diverseaudiences: ElectronicEngineering, L Studentsin Electricaland Computer Engineering. Technology EleclricalEngineering Technology, and Computer Engineering curricula.Twoscenariosfor studentsfitthe book very well. l.l Beginningstudentswho havenotyet had a C programmingcourse:The book servesa tlvo-semesteror four-quarter sequencein which students learn C länguageprogmrnminS,learn howto applyC to embedd€d microcontroll€r designs,andadvanceto the more sophisticatedembedded applicätions.Inthis instance,theprogramscan äll be run on än embedded microcontroll€r with very little hardwareknowledgerequired.After Chapter | , " EmbeddedC Language Tutoriall' is completed,it will serve as a proSrammingreferencefor the bälanceoi the courses. 1.2Studenrswho hävealreadytal€n a C programmingcourse can use th€ book for a one-semesteror two-quarter course in ernbeddedmicrocontrollers.ln this instänce.the studentsstudyon ly those portions of chapter I that relateto programmingfor the emb€dded€nvironmentand moye quicldyto the advancedhardwareconcepts.Chapter I is organized(asare all the €haptersin the book) to provide a usablereferencefor informätion neededin other courses. 2. Pr?cticingengineers,technologists,and techniciänswho wänt to add a new microcontroller to their areasof expenise:Chapt€r I can be usedas needed {dep€ndin8on the user! levelofprogramming experience)either to leärn n€ededconceDrsor as a reference.ThechaDtersabout theAtmelAVR micro_ controller hardwarewill leadsuchan individualthrough the stepsof learninga new microcontroller and serveas a referenceforfuture Droiects. PREREQUISITES Someknowledgeofdigital systerns,number systems,and logic designis required.Preliminary versionsofChapter l, "EmbeddedC LanguageTirtorial,' havebeenusedsuccessfully in a tundamental microcontrollers course (sophomore-1evel class*no prerequisite programming) following two semestersofbasic digital logic courses.It has also proven to be an ercellent tert for an advancedmicrocontrollers elective course.In many cases,the students have elected to keep the book and use it as a reference through their senior project desrs. courseslrnd have taken it with them into industry as a useful reference. ORGANIZATION The text is organized in logical topic units so thar instructors can either follow the text organization, starting with the C language and progrcssing through the AVR hardrare and into more advancedtopics, orcan choosethe orderofthe topicsto 6t their particularneeds. Topics ärekept separateand identifredfor easyselection.The chapterexercises and laboratory exercisesare also scparated by topic to make it ensy to select those that apply in any Dartrcularlnstnnce. CHAPTER CONTENTS SUMMARY ChapterI,Embedded C languageTutorial The C language is coveredin d€tailin a step-by-step methodas ir appliesto programming embedded micrccontroll€rs. One or mor€exampleprogmms accompany eächproSramming conceptto illustmteits us€.Atthe conclusion ofthe chapteistud€ntsare ableto createC languäge programs ro solveprobl€ms. Chapter2,TheAtmelRISCProcessors Th€AVRRISCprocessors arecoveredfrom basicarchitecture throughuseof all of the standärdperipheral devicesincludedin the microcont.ollers. Example programs are usedto demonstrate commonusesfor eachofthe peripherals. Uponcompletion ofChäptersI and2,studentsäreableto applyAvRRISCprocessors to solve Chapter3,Standärd l/O andPreproc€ssor Functions Chapter3 introduces studentsto the built-infunctionsavailable in C andto their us€. Agäin,example programsare usedto illustrat€how to usethe built-infunctions. Finishing Chapter3 pr€par€s studentsto usethe built-infunctionsto speedtheir programminS andeffonsat problemsolving. Chapter4,TheCodevisionAvR C Compil€randIDE Thischapteris the handbookforusingthe CodevisionAvR compiterandits accompanying integrated developmenr environment (lDE).Students canlearnro use the CodevisionAvR andits IDE€ff€ctiv€ly to createanddebugC programs. Chapter5.ProjectDevelopment of a Proiectusingmicrocontrollers. Thischapterfocuseson th€ orderlydevelopment in its entiretyto illustratethe A wirelessindoor/outdoorw$ther stationis developed their successes process. develoPProjectsto maximize Studentsleärnto efficiently complet€reference to the built-in Reference.A AppendixA, LibraryFunctions libraryfunctionsavailable at the time of publication. is the andthe STK500.This AppendixB,GettingStanedwith CodevisionAvR yvhen used with theAtmel STK500. quick-startguideto CodevisionAvR is a guideto actually theAVRl''licrocontrollers.This AppendixC, Programming that studentscan progrämming the FLASHmemoryar€aoftheAVRdevices,so function. understand the programming usersguidecoversthe andUsingTheCableAVR.This Appendixq InstallinS hardwareandsoftware. installation anduseofTheCableAVR Board Development AppendixE,Th€l4egaAVR-DEV AppendixF,ASCIIChäräcterTable. AppendixG,anassembly codeinstructionsummaryfor usewith the assembly examples. codeprogramminS Exercises AppendixH, Answersto Selected to installing the guideis a quickreference Appendixl, FastStartGuide.This programming uP and the härdware,and a simple softlvare, connecting Setdng goinganda l'legaAVR-DEV Development Board. RATIONAIE The advancing technology surrounding microcontrollers continues to provide amazingly have1edto the almost univergreateramountsoffunctionaliq, and speed.These increases sal use of highJevel languages such äs C to progmm cven time-cdtical tasks that used to require assemblylanguage pro$ams to accomplish. Simultaneously, microcontrollers have become easierand easierto apply, maling them excellent vehicles for educational use Many schoolshave adoptedmicrocontrollervehiclesas target devicesfor their courscs.And the price of microcontroller development boards has dropped to the level where a number of schoolshavcthe studentsbuy the board asa part oftheir'parts kit" so that all studentshxve their oün development board. Some ofthese coursesrequire C programming as a prercqui site, and others teach C languageprogramming and the applicationofembedded microcontollers in an integated mmner. This book is an answcrto the need for n text that is usablein coußes with and without a C language prerequisitc course and that can be a useful reference in later coursework. The CD-ROM included with this book contains the compiler and other softlvare so that studentswith their o$'n developmentboardshaveeverythingthey needto work outsidcof classasrvell asin the schoollabs. HARDWARE USED Most ofthe programming application examples in this textweredeveloped usingan AVR cvaluationboard providcdby Progrcssn'c Rcsourccs, LLC (rcfcr to Appendir E lor spccifics). This boardis particularly wcll suitcdfor cducetronal useandis a goodgeneraF areveryersytouse purposcdcvclopment board-However, theAtmelAVR microcontrollers andcanbc run perfcctlyrvellby simplypluggingthem into x protot)?eboard,addingthe oscillatorcrptal, alongwith two capacitors, and connccting four wircsfor programming. StLrdents havebeenverysuccessful with eithermettroo. The AIMega8535,ATMega8515,AIMega16, and AIMega48 microcontrollers have for the text.One of the majoradvantages of the AVR beenusedto rvorkout the examples microcontrollers is that they are parallelin theü architectureand the programming approach for the devices. This mernsthat the examples shownwill work on virtuallyany Atmel AVR microcontroller, andotherresources providedthat it containsthe peripherals to do thejob-it is not necessary to makechanges to usethe codefor othermembersof the AVR famill Consequentl)-, the text is usefulwith other membersofthe AVR family xswcl1. The morecommonperipherdsarecovered by this te:'t,.rndthe codecanbeusedm a tem plateto applyto morearoticperipherals in someof the otherAVR familymembers. CD-ROM CONTENTS AND SOFTWARE USED IN THE TEXT Thc softrvarc uscd with thc tcxt includcs thc Atmcl AVR Studio (&ee from http://wrvwatmcl.com/)and thc CodcVisionAvR C compilcr from I"IP InfoTlch S.R.L. (evaluation version fiee from http://wrwhpinfotech.rol). All of the programs in thc tcxt can be compiledrnd run using the includedevrlurtion versionofCodeVisionVAVR. The CD-ROM included with this book containsthe sourcecode for all of the softwue examplesfrom the text. These can be used as referencesor as starting points for specific assignmcnts. Also includcd on thc CD ROM is the CodcvisionAvR e\'aluationversion compilcrthat was curcnt at the time ofpublication.Also refer to the Wcb sitc information to obtain the latest version of the compiler.More inlormation about purchasingthc fu1l version mav be found at htto://wu.rv.orllc.com/. AC KN OWLED G E M E NTS 1'hematerialcontainedin this text is not onlv r comoilationofvearsofexoerience but of inlormationavailable from Atmel Corporrti"n.r-."i T..lna"g Syste'niInc..PL"grer sn'eResources LLC. andHP InfoTlch S.R.L. Atmel Corporation 2325 OrchardPukway SanJose, CA 95131 1-408-441-0311 http://wur. atmel.com PavelHaiduc HP lnfoTech S.R.L Str.Liviu Rebreanu134 ts1.N20 Sc.BAp.5B Sector3 Bucharest746311 ROMANIA http://wwwhpinlotech.rol ForestTechnologySystcms,Inc. SuiteIl4131 Mitchell Wa1. Be[nrgham,WA USA 98226 FTS ForestTechnologySystems Ltd. 113 2924JacklinRoad Victoria,BC CanadaV9B 3Y5 Phone:1 250 ,1785561or 1 800 548 4264 Far:1 250 478 8579or 1 800 905 700,1 http://uwv..ftsinc.com/ AUTHOR-SPECIFIC Progressive Resources LLC fPriio] 4105VincenlesRoad Indianapolis,IN46468 1317-471,1577 http://urrv.prllc.com/and http://ur,!\Ä'.priio.com AC KN OWLEDG E M E NTS Thc support of my famlly, Gay, Laun, and April, has madc this book both a plcasurcto work on and ajoy to complete.lt is alsoimportant to acknowledgethe motivation supplied byLarry O'Cull and thc fantasticpleasureofworHng with Lary and Sarahon this projcct. RichardH. Barnett, PE, Ph.D. May2006 It was a great plersureto work on this pro.jectwith Dr Barnett, teacherand rnentor,rnd S.rrahCox, p:rtner rnd co-al,thor.The)' kept thn project exciting.This work u'ould not havebeenpossiblewithout the paticnccand supportof my wil-e,Anna, and children,Jrrnes, Heather,Mrx, and,A1an,who havebeenwilling to give up somethings norvto build bigger Larr,vD. O'Cull Mav2006 This bookhlrsbeen a challengingand cxcitingendeavorI havea tremendousamountofrespcct t'ör Lffry O'Cull and Dr. B.rrnett and have considercd it a great privilege to work with them. I must specilicallythank Larry for having the vision lor rhis project.I alsowant to thank mv husband,Greg, daughterMeredith, and son David, lor their supportthroughotlt SarahA. Cox May2006 AUTHORS 1tis text is dcfinitely a highly collaborative rvork by the three authors. Each section rvas Iargely *-rittcn bv one author and then critically reviewed bv thc other trvo, who rewrote chunksasneeded.It is not possibleto delineetcwho is responsiblcfor any particülarpartof the book.The authorsi Ri.hürn H. Barnett, PE, Ph.D. Pra|i sso af Ehttüa/ Engin eering Teehna/ag1 Dr Barnetthasbeeninstructingin the ercnofembeddednicrocontrollersfor thc pasteightecn )rcars,stffting with the Intel 8085,progressingto sevcralmembersofthe 8051 family of embeddedmicrocontrollers,and norv teachingAdvanced EmbeddedMicroconrroliers using the Atmel A\ß. devices.During his summersand trvo sabbaticalperiods,he worked extcnsivelywith multiple processorcmbedded systems,applying them in a rarieq' of control oriented applications.In addition, he consultsactivelyin the licld. Prior to his tcnure rt PurdueUniversigl he spentten yearsas an cngineerin the aerospace electronics industry In terms of teaching,Dr Bamett has rvon a nutrber of tcaching awards,including the CharlesB. Murphy Award asone ofthc bestteachersat PurdueUniversity.He is alsolisred on Purdue Unn'ersity\ Book of Great Teachers,a list ofthe 225 most influcntinl teachers overPurdue'sentire history This is his sccondtext. He maybe contactedwith suggcstions/comments at PurdueUnivcrsiryat765-494-7497or by email at rbarnett@purduc.edu. Larry D. O'Cu// Sen;or O?erutingMe nlr €r Progrest ;ve Raaur ru LLC Mr O'Cull receiveda B.S. degreeftom thc SchoolofElectrical EngineeringTichnotc,gy at PurdueUniversity.His careerpath startedin the designof softwareand control systems for CNC (compLrternumeric controllcd) machine tools. From there he movcd to other opportunities in electronicsengineeringand software developmentlor vision systems, LASER-robotic machinetools, medical diagnosticequipment,nnd cotrmercial and con sumerproducts,and he hasbeenlisted rs inventor/co-inventoron mrnerous prtents. Mr. O'Cull startedProgressive Resources in 1995 after severalycarsofl'orking in Elcctri cal md Sofnvrre Engineernrgand EngineeringNltanagement. ProgrexiveResourccsLLC, now Priio (wwv.priio.com),specializes in nrnovrtivecommercia|industrial,md consumer prodLrctdeveloprnent.Priio is an Atmel AVR consultantmember. bi, email at ldocull@priio.com. Hc mxl bc contactedwith suggestions/conments SarahA. Cox Dneclor af Sa-ft.rateDevetoPnent Pragres:it e Re:oureesLLC Ms. Cox has a ßachelor of Sciencedegreein both Computer and Electrical linginccring from PurdueUniversiq; wherc shc locusedher snrdieson sofnvarcdcsign. After a short careerfor a large consultnrg6rrn working on databasemamagement sysrems, shervaslLrredrway by the fast pacernd the infinite possibilitiesofmicroprocessordesigns. Shc *-orkcd independentlyon veriouspiecesofmedical test equipmentbeforebeconing ä LLC. partnc! at ProgrcssiveResources At Progressn'e Resources, .vls. Cox hrs developedsoftwarefor projectsnnging äom small consumerproductsto industrial productsand test equipment.Theseprojecs havespanned severalfelds, rmong them .lutomotive,medicr , entertrinment,child development,public safegv/education, sound rnd inage compression,and construction.rUong the n'ay she has beenlisted as co-inventoron numerouspatent rpplications.She has rlso written the soft w.rrelor in-systemprogrmming rnd developmenttools targetingAtmel AVR processors. She may be contactedwith suggestions/comments byemail at scox@priio.com. An embcddedmicrocontrolleris a microconputer that contdns most ofits periPheralsand requiredmemory inside a singleintegratedc;(cuit alongwith the CPU. It is in actualiq" a microcomputeron a chip." Embeddedmiuocontrollershavebeenin usefor more than threedecxdes.TheIntel 8051 serieswas one of thc flrst microcontrollersto integratethc mcmory,I/O, arith netic logic unit (ALU), program ROM, rs well as someother pcripherals,all into one very neat little package.Thcsc processorsare sti1l being designed into new products. Other companiesth:rt followcd Intel's lead into the embeddedmicrocontroller nrcnx we(e GenerJ Instruments, National Semiconductor,Motorola, Philips/ Signctics,Zilog, AMD, Hitrchi, Toshiba,and Microchip, amongothers. In recent years, Atmcl has become a world leader in thc development of FLASH memory technology FLASH technology is a non volatile yet reprogrammable memory often usedin productssuch as digital cameras,portableaudio devices,and PC motherboards.This memory technologyreallypushedAtmel aheadin the mi crocontroller industry by providing an in-system programmablc solution. This, cou pled with the developmentofthe AVR RISC (reducedinstuction set comPuting) core architecture, provides lor vcry low-cost yet amazing solutions. The next great stcp in this high-tech evolution was thc implementation ofhigh lcvcl languagecompilcrs that ue targeted speciAcallyfor usewith these new microproccssors.Thecodegenerationand optimization ofthe compilersis quite impressive.The C programming languagc, with its "make your own rules" structure, lends itself to this application by its ability to be tailored to a particular tnrget s]ßtem, while still al lowing for code to be portablc to other systems.The key benefit of a langr.rge like this is that it createspools ofintellectual propertythat can be drawn from agdn and again.This lowersdevclopmentcostson an on-going basisby shorteningthe devel opment cyclewith eachsubsequentdesign. One ofthe linest C langragetools developedto dateis CodeVisionAVR.Written by Pavel Haiduc ofHP InfoTech S.R.L., this completelyintegrateddn)ela?ment envirannent(IDE) allows editing, compiling, part programming, and debugging to be performed from one PC Windows applicrtion. Thc motivation that hasled to the developmentofthis book is the growing populariq' of the AVR md othef RISC microcontrollers, the ever increasing level ofintegration (more on a chip and fewer chipson a circuit board),and the nced lor "tuned thinkinq" when it comes to developingproductsutilizing this type oftethnologl. You mayheveexpfricncewriting C lor a PC, or assemblerfor a microcontroller.Butwhen it comesto writinE C for an embedded microcontroller,the approachmust be modified ro get the desiredftnat resultq:small, efficient,reJiable,reusablecode.This text is designedto providea good baselinefor the oeginner aswell as a helpful referencetool for those experiencedin embedded microcontrotler Embedded C Language Tutorial t.t oBJEcTlvEs At the conclusion of this chapter, you should be able to Defne, des€ribe,andidentiryväriableand coDstanttyp€s,their scoPe,anduses Construct variableand constantdeclantions for allsizesofnumeric dataand {or strings Apply enumentions to variabl€declarations Assignvaluesto väriablesand constantsby m€ansofthe assignmentoPerator Evaluat€the resultsofallofthe op€rators usedin c Explain the r€sults that each of the control stat€ments has on program flow Create functionsthat are composedof variables,operators,and control stateunions as function variables Apply pointers,arräys,structures,and Creat€ C programsthat complet€task usingthe conceptsin this chapter I.2 INTRODUCTION This chapter provides a baseline coursein the C programming language as it applies to embedded microcontroller applications. The chapter indudes extensions to the C langüage that are n part ofthe CodeVisionÄVR@ C language You will go from be ginning conceptsthrough rvriting complete programs, with oramples that can be im plemented on a microcontroller to further reinforce the material The information is presentedsomewhatin the order that it is neededb]' a Programmer: . Declaringvariablesand .onstants . Simplel/O, so that prognms can make use of the parallelpons of the 2 ' AssigninSväluesto the väriablesand constants,and doinSarithmetic operationswith rhe variables . C constructsand controt stätementsto form complete C programs The linal scctions cor,'er rhe more advanced topics, such as pointers, arrays, structures, and unions, xnd their use in C programs. Adranced conccpts such as real-time programmn,g and irtcmrpts complete the chapter. I.3 BEGINNING CONCEPTS Witing a C programis, in a sense,like building a brick house:A foundation is laid, sano and cement arc used to make bricks, these bricks are arransed in rows to make a course or bloclis,and the coursesare thcn stackedto creat<a building.In xn enbedJcd C progrm, setsofinstructions ffe put togetherto form firnctions;thesefunctions are thcn treatedas higher lcvel operations, rvhich are then combined to form a prograrn. Everv C language program must ha\a at leasr one tunction, namelv zaä!. The function naizll is the foundation ofa C languageprogram, and it is the starting poinr *-hen the program code is executed.All tunctions are invoked bv nain) eithcr directl,t or indirectly. A1 though functionscan be completeand sclf contained,variablcsand parameterscan be uscd to cementthesefunctions togerher The tunction zaä(l is consideredto be the lorvestlevel task, sinceit is the frrst tunction callcd ftom the system starting the program. In manv cases,zaizll will conrain only a ferv statemcntsthrt do nothingmore thaninitialize and sreerthe operationofthe progam from one function to another. An embeddedC program in its simplest form appearsas follows: I ] The program shown abovcrvill compile and operateperfectly but you will not knorv that for sure,bccausethere is no indication of acriviryof any sort.We can embellishthe program such that 1,oucan actuallv seelife, revicrv its functionrlilv, and begin to studv the syntacü cal elementsofthe language: +include <stdio.h> !,rinti( ihile{l) Hal,to I'ORLD"); /* the cLassic // do fareveL-- C Cest program. Enbedd.d C Lanquate 711tarial This program will print the words "HELLO WORLD" to the standard output, which rc most likely a serial port. The microcontroller will sit and wait, forever or until the micro controller is reset.This demonstrates one ofthe major differences between a personal computer program and a progrnm th"t is designed for an embedded nicrocontroller: nrmely, that the embedded nicrocontroller applications contain an in6nite loop. Personal comPutcrs have an operating s)'stem, and oncc a program has executed, it retums conüol to the operating systemofthe conputer. An embeddedmicrocontrolle! however,does not have an operating systemand cannot be allowed to fall out oftlrc program at any time. Hence, every embedded microcontroller application has an infnite loop built into it somewhere,such as tha uhile(1.) 1n the ex mple abor.e.This prcvents the program ftom running out ofthings to do and doing random things that ma1,be undesirable.The while construct will be exPlained in a later section. The erample program also provides an instance of the fust of the common PreProcessor compiler directives.#indude tells thc compiler to include a 61ecalled stdio.h asa part ofthis program. The tunction p rintf} is provided for in arr artemal library and it is made availahle to us becauseits definition is locatcd in the stdio.h 61e-As we continue, these conceptswill come together quicH). These are some of the elements to take note ofin the orerious examples: A semicolonis usedto indicatethe end ofan expression.Anexpression in its simpl€stform is a semicolonalone. {} Bnces "0" a.e usedto d€lineatethe beginningand th€ end of th€ function! contents.Bra€esare also usedto indicatewhen a seriesof stat€m€nts is to be treated as a single block. Double quotes are usedto mark the beginningand the end of a text stnng. ll or l* ...*l are usedascommentdelimiters. Slash-slash or slash-star/star-slash Comments arejust that, a programmerk notes. Comments are critical to the readabiJityof a program. This is true whether the Foglam is to be readby others or by the original programmer at a later time. The comments shown in this text are used to erplain thc function ofeach line ofthe codein the example.The comments should alwaysexplain the actu^lfunet;an of the line in the prcgram, and notjust echo the specilic instructions that are used on the line. The tr.aditionat comment delimitcrs arethe slash-star(ö, star slash(.4 conliguration. Slashstar is used to create block comments. Once ä slash-star (F) is encountered, the compiler will ignore the subsequenttu.t, wen if it cncompassesmultiple 1ines,until a star-slash(? is encountered.Refer to the frrstline of the ruinj irnction in the previous progam example for an arample ofthese delimiters. The slash slash (/4 delimiter, on the other hand, will causethe compiler to ignore the comment te),1only until the end of the line is reached.These are used in the second line of the nain) frnciron of the exampleprogran. 4 As we mor,.einto thc details, a fel. svntactical rutes and sone basic telninology should be . An identifier is a variäbleor function name made u p of a teEer or u nderscore ( ), followed by a sequenceof lene.s and/or digitsand/or underscores. . ld€ntifiersare cäsesensitive. .ldentifierscanbean/length,butsomecompitersmayrecognizeontyatimitednumber of charäcters,suchas rhe firsr rhirry,rwo.So beMre! . Pardcularwords havespecialmeaningto the compiter änd are consideredreserved words.Thesereservedwords must be enreredin towercäseand shoutd nevef be used as identifiers.TableI-l lists reserueoworas. \drilc if void Tabl€ l-l ' I.4 Reseryedword Lst SinceC is ä free-fo.m languä8e,"whitespace"is ignoreduntessdetineatedby quotes. This includesblank (space),tab,and new tjne (catriagereturn and/or tine feed). VARIABLES AND CONSTANTS It is timc to look at data storedin the form ofvariablcsand constants.Variables,as in algcbra, are valuesthat can be changcd.Constantsare 6-xed.Variablesand constantscome in many forms,,rndsizes:rhevaJeqtoredin rheprogramirmemoryin a variegvoflorms that will Deexamrneoaswe go a1ong. I . 4 . I V A R I A B L ET Y P E S A variableis declarcdbv the rcsened rvord indicating its lype and size followed by an identillcr: unsasned char peabody; inL doqs, catsj Long inr toLal dogs and_cals; Värixblesand constantsare storedin the limited memorv ofthe microcontroller,and thc compilerneedsto knos' horv much mcmory to sct asidefor cachvariablewithout wasürg E n b . d d . d C L a n g t u a g eL t a t t d l S Consequendy, a programmermust declar€the v'ariabl€s, specmemoryspaceunnecessarily. ifyingboththesizeofthevatubleandthetypeofthevariable.Tablel2listsr€riableq?es aod their associated sizes. TyPe Stze(8itr) 1 8 8 8 16 0,1 'L2a6 \27 0toä5 -124 6 P7 -32764632767 -32764632767 16 l6 32 32 32 32 32 Table l-2 0 to 65535 32768ro32767 b 2147443647 21,47483644 0 to 4294967295 2147483648to 2147483647 ir.175c 38 to i.402e38 i1.175e38 to $-402e38 Yo"?bleTvDes ond SizF I.4.2 VARIABLESCOPE As noted above,constants and variables must be dedared prior to their use.The stEe of a variable is its accessibility within the program. A variable can be declared to have e\t\er latal Local Variable.s Local variables are memory spacesallocated by the function when the function is entered, g?ically on the program stack or a compiler-created heap space.These variables are not accessiblefrom other functions, which meanstheir scopeis lirnited to the functions in which they are dedared. The local variable declaration can be used in multiple functions without conflict, since the conpiler seeseach ofthese uriables as being part ofthat function only. Global Variables A global or extemal variable is a memory spacethat is allocat€d by the compiler and can be accessedby all the tunctions in a program (unlirnited scope)-A global variable can be modifred by any function and will retain its r"lue to be used by other tunctions. Global variables are gpically deared (set to zero) when nain) is started.This operation is most often perfomed by startup code generatedby the compiler, invisible to the programmer. Arr example piece ofcode is shown below to demonshate the scopeofuriables: unsigned void char slobey; function unsigned z int (void) //a qlobal is //rhis tseen; variable a funclion loca1 //a // // This cal1ed fron naino variabLe because rween is locaL because qlobey is g1oba1 qenerare will an error mdin lo. s'o -- -o n"ir. //oK //oK tine be.dus- l I nain globey treen = l4; = 12; toc; //a variable 1ocal //ok b-^d"sa //wi11 cause // to function z Eo matn{) :s c q_ob.. srob-/ tseen is locaL tuhi 1e ( 1) J When variables are used within a function, ifa local wriable has the same namc as a slobal variable, the local wiJl be used by the function. The value of rhe global variable, in thii case, will be inaccessibleto the tunction and will remain untouched. 1.4.3 CONSTANTS As described earlier in the text, constrnts äre fixed values-they may not be modified as the progralr executes-Constants in many casesare pan ofthe compiled program itseli located in read-only memory (ROM), rather than an allocated area ofchangeable random access memory (RAM). In the assignnent . = I + y; the number J is a constant and wi[ be coded direcdv into the addition oDeration bv the compiJer.Con.tants can alsobc in rhe form ofcharacrersor a 'tring ofrew: p r i n t f ( " h e 1 1 ow o r l d ) , . // // // // 'helfo text wortd" is placed in and never chanses ,B, is pernanentty The tetsLer set in proqran memory. The prosram nenoiy You can also dedare a constant by using the rescrvedword const and indicating its qpe and size. An identiEer and a value are required to complete the dedaration: constcharc=5?; Enbedded C Langtage T"tarial Identi$ing a variable as a constant w;ll causelhat variable to be stored in the program code spacerather than in the limited variable storagespacein RÄM. This helps preservethe limited RAM space. Numeric Constants Numeric constants can be declared in manywals by indicating their numeric bas€and making the program more readable.Integer or long integer constants may be written in . D€cimalform withouta pr€frx(suchas 1234) ' Binaryform witn 0b prefix (suchas0b | 0 | 00 | ) . Hexadecimalform with Ox pr€lix (suchas oxff) . Octalform with 0 prefix Guchas0174 There are also nodifers to better defne the intended size and use ofthe constant: . Unsisned inteserconstants canhavethe sufFxU (suchas 10000U). . LonginteSerconstäntscanhav€th€ sutrx L (suchas 991). . Unsignedlong integerconstantscan havetie sufüxUL (sucha599UL). . Floatingpointconstants canhavethe $mx F (suchas 1.2340. . Character€onstants mustbe enclosedin singlequotationmark, 'ar or'A'. Character Constants Chancter constants can be printable (like 0 9 aad A Z) or non-printable chaJacters(such as new line, cariage return, or tab). Printable character constants maybe enclosedin single quotation marks (such as a'). A backslash followrd by the octal or hexadecimal value ln single quotes can also represent character constants: can be represented by '\16{' can be rep.esented by '\x74, Table 1 3 lists some ofthe'tanned" lan$age. non printable charactersthat are recognized by the C Baclslash (\) and single quote O charactersthemselvesmust be precededby a backslashto ' avoid confusing the compiler. For instance,\ is a single quote character and N is a backslash.BEL is the bell character and will make a sound when it is received by a computer terminal oi terminal emulatol I,4,4 ENUMERATIONSAND DEFINITIONS ReadabiJiryin C programs is very irnportant Enumerdions and definitions are provided so that the prcgrammer can reptacenumbers with names or other morc meaningfirl phrases. 7 8 Equivalent Hexyolue '\x07 BEL '\08' TAB \09' LF (nry lirc) \0a' \'"1' '\f FF CR Tabfe l-3 Nor?rintobreChoto.terNotodons Enumerations are listed constants. The reserved word enum is used to assign sequential inrFgercon.rinr \"alue"ro a Iisr olidenrifers 1nt nun_va1; //declare an enuneration / /decLare enum { zero val, one va1, num va1 = two_val; 'fhe two // an inteser wa1, the Ehree sane as: va1 variable )t num va1 = 2; name zeratal ls *signed a constant value of O, one_oalof 1, tua oal of2, and so on. Ar initial value may be forced, as in enum { slarr=10, next1, next2, enal wa1 }; which will causetn"l to have a value of 10, and rhen each subsequent name will be one gte rer nextl is 11, noct2|s 12, nd. end:tal is 13. Enumerations are used to replacepure numben, which the prograrnmer would have to look up, with the words or phrasesthat help describe the numbert use. Definitions are used in a manner somewhat similar to the enumerations in that rhey will ,]]ow substitution oforc tex-tstring for another. Observe the following arample: on = 1, { red_led *define leds PORTA enun PORTA = 0a1; Leds = red-led 'lhe"#defne sreen-ted turn //neans on; //neans on, both leds_on t, tshe real LED on Ehe sane rhins kds PORT4"Iine causesthe compiler to substitute the label PORD4 whercvet it encountersthe rvord /sd. Note tlnt thc #defne line is not ended with a semicolon and may not have comments.The enumeration setsther"alue ofred led on to 1,green_hd_onto 2, and batb-htls an to 3.Thts mglt be used in a program to control tie red and green LEDs where outputting 1 turns the red LED on, 2 turns the green LED on, etc. The poinr is that "1r* = red )ed an" is mtch easlerto understand in the program'scontc\t than "PORT4 = 0ir7". Eflbrdd.d C Languag? Tu!oriat #deÄne is a preprocessordirective. Preprocessordirectives are not actually part ofthe C language syntax, but they are accepted as such becauseof then use and famiJiaity. The preprocessoris a step separatefrom the acnral compilation ofa program, which happensbelore the actual compilation begins. More information on the preprocessor can be found in Chapter 3, "Standard I/O and PreprocessorFunctions." I.4.5 STORAGECLASSES Variables can be declared in thrce storagc classes:auto, static, and register. Auto, or auto matic, is the default class,meaning the reservedword auto is not necessary An automatic classlocal variable is uninitialized when it is allocated, so it is up to the progranmer to make sure that it contains valid data before it is used.This memory spaceh releasedwhen the tunction is exited, meaning the valueswill be lost and will not be valid ifthe function is reentered. An automatic classvariable dedaration would aooear as follows: auto int ln! value value 1; 1; // This is the cormon, default forn, Static A static local rariable has only the scope of the tunction in which it is denned (it is not accessibleftom other functions), but it is allocated in global memory space.The static vari able is initialized to zero the fust time the function is entered, and it retains its value when the function is exited. This allows the variable to be current and valid each time the furc sEa!ic int value-2; Register A register local radable is similar to an automatic variable in that it is uninitialized and temporary The difference is that the comdler will try to use an actual machine register in the microprocessor as the rariable in order to reduce the number ofmachine cycles required to accessthe variable. There are very few registersavailabtecompared to the total memory in a gpical machine. Therefore, this would be a class used sparingly and with the intent of speedingup a particular process. I.4.6 TYPE CASTING There are times when a programmer might wish to temporarily force the gpe and size of the variable. Tlpe casting allows the previously dedared type to be overidden for the duration of the operatiofl being performed- The cast, called out in parentheses,applies to the exoressionit orecedes. 9 t0 Giren rhe folJowingdeclarations andassignment. // // // // a sisned, 16 bit inteser a sisned, 8 biL character (but its x is an inEeqer, i^La a chalacLer) | 3216A ta +32161) I L2n ta +a27) value wilL fit t)?e cast operations on these variables could appear as // x // // anal Lhe walue is y is extended up assigned to x. // is conwerted to a character a4d then y. then pLaced into to an integer, and Tlpe casting is particularly important when arithmetic operations are performed with vari ablesof diflerent sizes.In many cases,the accurac_v ofthe arithmetic will be dictated by the rariableofrhe smalJesr wpe. Considerthe tol[wing: v - 63; // // d.eclare aleclare and and initialize iniLiallze r y z-ly+14)+x; As the compiler processesthe right side ofthe equation, it will look at the size of1 and make the assumption that f . -1o./is a character (8 bit) multiplication. The result placed on the stack will have exceededthe width of the storage location, one \te or a value of 255. This will truncate the value to 118 (0x76) instead ofthe correct value of630 (0x276). In the ne{t phase of tie evaluation, the compiler would determine rhat the size of the operation is integer (16 bits) and 118 would be ertcnded to an integer and then added to r. Finall_n : would be assigncd268 . . . WRONG!! Type casting should be uscd to corüol the assumptions.Writing the samc arithmetic as z=((int)Y*10)+x; will indicate to the compüer that1' is to be treated as an integer (16 bits) for this opcration. This will place the integer value of630 onto the stack as a result ofa 16-bit multipLication. The integer rzlue r will then be added to the integer valuc on the stack to cfeate the integcr result of 780 (0x30C). :: will be assignedthe value 780. C is a very flexible language.It will giwepu what vou ask for. The assunption the compilcr will make is that you, the programmer, know what you want. In the etample above,if the value ofl werc 6 instead of 63, there would have been no erors. \j!y'henwriting e\pressions, you should alwal's think in terms of the maimum r,alucsthat could be given to thc expres .:on ,rndwhat the resultingsumsand productsmay be. A good rule to follow: 'When it doubt-cast it out." Afiiqß cast the variables unless you arc surevou do not need to. Enbedd.d C Lantrage Trtotid/ I.5 I'O OPERATIONS Embedded microcontrollen must interact direcdv with other hardware.Thereforc. manv of their input and output operations are acmmplisherJ uslng the builc-in pa.ra.llelpons oithe microconfioller. Most C compilers provide a convenient method of interacting with the paralel ports through a library or header lile that uses the sftb and sfrw cornpiler commands to assign labels to each of the parallel ports and other VO devices.These commands will be discussedin a later section, but the examole below will serve to demonstrate the use of the pärallelports: < M E G A 85 l 5 . h > +include void // reqrisEe! definition // a4 Atnel ATMega8535 header file for main(void) set a1t bits vhile of porE B for outspuE (1) I z = PINA; // // .ead the binary port a pins (i-e., // srite plus // the 1 to value inpuE binary value port B read f.on porl A The exarnple above shows the methods to both read and writ€ a parallel port. z is declared as an unsigned character size variable becausethe port is an 8 bit port and an unsigned charactervariable will hold 8-bit data. Notice that the labels for the oins ofoort A and output port B are aI capitalizedbecausetheselabelsmusrmarch the wäy tbe label. aredefined in the includedheaderiile MEGA8535.h. The DDRr registeris usedto determinewhich bits ofportx (A, B, and so on depending on the processor) arc to be used for output. Upon rcset, all of the I/O pofts default to input by the microcontroller writing a 0 into all the bits ofthe DDRx registers. The programmer then sets the DDRx bits depending on which bits are to be used for output. For // // ser Lhe uppe.2 and tower oE pott B for output 2 bits This examptecoffigures the upper two bits and the lower two bits to be used as output bits. tl t2 I.6 OPERATORS AND EXPRESSIONS An arpression is a statement in which an operator linla identifers such that when evalu ated, the result may be true, false, or numeric in value. Operators arc sltrbols that indicate to the compiler which type ofoperation is to be performed using its surrounding identifiers. There are rules that apply to the precedenceor order in which operations are performed. When you combine operatorsin a single expressionthose nrles ofprecedenie mu,t be applied to obtain the desired result. I.6.I ASSIGNHENTAND ARITHMETIC OPERATORS Once variables have been declared, operations can be performed on them using the assig!ment operator, an equal sign (=). A value assignedto a variable can be a constant, a variable, or an expression.Arr erpression in the C languag€is a combination ofoperands (identifers) and operators.A t}?icrl assignment may appear as follows: dos = 35' va1 = dos; doq=dos+0x35; : (2 * \do.J + 0112)) var = y (n * x) + b; + 6t The compiled program arithmetically processesexpressionsjust asyou would processthem by hand. Start from inside the parenthesesand work outward ftom teft to right: In the above exprcsslonf = fu. i + b, the zr arrd r would be multiplied together tust and then added to l;6nally,ywould be assignedthe resulting mlue In addition to the parentheses,there is an inJrerent precedence to operators themselves. Muttiplication and division ar€ perFormed first, followed by addition and subtraction. Therefore, the statement v = m - x + b; is evaluated the sameas y = (n r x) + b; It should be noted that the use ofthe parenthesesimprovcs the readability ofthe code. Table 1-4 shows the qpical arithmetic ope€toß in order ofprecedence. Multiply Divide % Subtraaion or Negrion Tä,ble 14 Atitllnetk ODerotots There areother g?es ofoperators besidesarithmetic and assignmentoperators.These include bitwise, logical, relational, increment, decrement, compound assignment,and conditional. Enb.dded C LanExa{e Tutaria/ t3 Bitwise Operators Bitwise operators perform functions that will affect the operand at the bit lev€l. These operators work on non-floating point operands: char, int, and long. Table 1-5 lists the bitwise operators in order ofprecedence. Left Shift Right Sbift AND 6. Fxclu;vc OR OR (Incluive OR) Table l-5 BitwtseODerorors The following is a description ofeach bitwise operator: . The onescompl€ment operatorconvensthe bitswirhinan operandto I ifthey were 0,andto 0 il rheywere l. ' The left shiftoperatorwill shiftthe left operändto the be in a binaryfashion, the numberof timesspecifi€d by the rightopedd.In a left shiftoperation, zerois always shiftedin replacinSthe lower bit positionsthat would havebeen"empty."Eachshift leli effectivelymulripliesthe operandby 2. 'TheriShtshiftoperato.willshifttheleftoperandtoth€right,inabinaryhrhion,the numb€rof tim€s specifiedby the right operand.Eachright shift effectivelyperforms a divisionby 2.\ r'hena rightshiftis performed, s8n€dandunsigned viriablesare treated diff€r€ntly.Thesignbit (the left or most signilicäntbit) in a signedintegerwi be rcplicated.Thissignextensionallowsa positiveor negativenumberto be shifted rightwhil€maintäinin8 rie sign.Vr'hen an unsiSned variableis shiftedright,zeroswill alwaysbe shiftedin f.om the left. . TheAND operatorwillresultin ä | at eachbit positionwh€reboth operands wer€ L . The €xclusive OR operatorwill resultin a I at eächbit positionwherethe operands ditrer(ä 0 in ore operandanda I in the other). . The OR (inclusiv€ OR) operarorwill resultin a I at eachbit positionwhereeitherof the opemndscontain€d a l. Table 1-6 gives some examplesofbitwise operatrom. Assume that an unsiened clraracter v = 0xC9 x = Ox36 r=) " li x=on}c x=v&0\3I; x = 0rC8 x = 0xD9 x=! | 0110; Table l-{ Exomp,es of&'rwiseOperoürons The AND and OR bitwise operators are uselirl in dealing with parallel ports. Observe thc following erample: + include <MEGA85l5.h> uns iefned char void //.eqister // an atmel definition file ATMEGAS5I5 for z; main {void) { DDRB = oxf f; Z=PINA&OX6; PoRTB = PoRTB | 0{60; PORTB=PORTB&oxfe; // set aII bits of port B for output // Read the blnary vaLue on the / / p o r r a p i n s A N D e dw i t h 0 0 0 0 0 1 1 0 . // write the binary value fron porE E // oRed with 01100000back ro porr B. // lirite the binafy vaLue fron porE B // ANDed uith oxfe to PoRTB. ) The erample abovedemorctates nasAing md b;taDie?ort eantrot.M^st<1ngis the techniquc used to determine the value of certain bits ofa binarv value. In this case,the masking is accomplished by ANDing the unwanted bits with 0 ( n AND 0 always results in 0) and the bits ofinterest with 1 ('*'AND 1 alwaysresults in 'x). In this way, all the bits cxcept for the cenLerrwo bir, of rhe lo$er n;bblearediminaleJ{serro 0). Bitwise port control is a method of changingone or more bits ofa parallel port without affecting the other bits of the pon. The 6rst POR?3 line demonstrates using thc OR operator to force two bits of the pon high without affecting the other bits ofthe port. The second POR73 line sho*s how to forc€ a bit of the port low by ANDing the bit with a 0. I.6.2 LOGICAL AND RELATIONALOPERATORS Logical and relational operators are all binary operators but yield a result that is either TRUE or FALSE. TRUE is represented bv a nonzero vatuc, and FALSE by r zero valuc. Embedd.d C La"gaage Tttaridl These operationsare usually used in control statementsto guide the flow of program Logical Operators Table1-7 showsthe logical operatorsin orderofprccederce. && Ar\D OR Table l-7 togkdi Operotors These differ greatly fion the bitwise operators in that they deal with the operands in a TRUE and FALSE sense.The AND logical operator yields a TRUE ifboth operands are TRUE, otherwise, a FAISE is the result. The OR logical operator yields a TRUE if either of the operators is TRUE. In the caseof an OR, both operators nust be FALSE in ords for the result to be FALSE, To illustrate the difference: Assune x = 5 andy (x {x (" (x = 2j && y) & y) is is l l y) I y) are zero, ANDed bitwise is non-zero value is TRUE, because eithe! 101b and 010b is TRUE, because the patle.n is 111b (non zelo). Inclusiwe-oRed t'iEvise TRUE, because both FALSE, because the ale non-zero. patstsern 101L' and 010b Relational Operators Relational operators usc compaJisor operations. As in the logical operators, the operands are evaluatedleft to right and aTRUE or FALSE result is generated,They effectively "asP' about the relationship of two expressionsin order to gain a TRUE or FALSE reply. ''rs "Is the the left Left greate! less lhan rhan or the right?' equal to rhe Table 1-8 shows the Relational operator. ls Equal to Is Not Eqo,l to Les Thm or Equ,l to GrcatüThm or Equal to Table l-8 R€lstto'o,Operdtors riqht?' 15 Exarnples are presented in Table 1 9. Assumethatx=3andy=5. [ALSE TRIJD TRTID TRTJD FAI-SE (, r=y) FALSE Täble l-9 Exdmples of Relotionsl Operctions 1,6.3 INCREMENT,DECREMENT,ANDCOt',tpOUNDASS|cNTIENT When the C language was devdoped, a grcat efort.\.\,.asmade to keep things concise but clear. Some "shorthand" operators were built into the languageto simplif the generation of statementsand shorten the keystroke count during progam development. These operations include the increment and decrement operaton, aswell ascompound assignment operators. Increment Opemtors Increment operators allow for an identifer to be modfied, in place, in a pre-increment or post increment manner For example, x = x + t; // pre // post increment increnent operation ope.ation In this cxample, the ralue is incremented by 1. ++r is a pre-increment opemtion, whereas r++ is a post increment operation. This means that during the erzluation of the expression by the compiled code, thc value is changed pre-waluation or post-evaluation. For example, k=2ri++; // at conptetion, k = 2 ana i=2 k=2*++i; // aL conpletion, k = 4 and i=2 In the fust case,i is incremented after the expressionhas been resolved.In the second casc, lwas incremented before the expressior was resolvcd. Enbedded C LanELdEe Tatarial Decrement Operators Decrement operators tunction in a similar manner, causing a subtraction of one operation to be performed in a pre-decrement or post-decrem€nt fashion: // i =. r i | // i = a r at Compound Assignment Operators Compound assignment opentors are another method of reducing the amount of syntax required during the construction of a program. A compound assignment is really just the combiniog of an assignment operator ( = ) with an arithmetic or logical operator T he expression is processed right to left, and syntactically it is consüucted somewhat like the increment and decrement opemtors. H€re are some examples: a += 3, b..=2i // a = a + 3 //x,=b-2 d. /= // a; d = d / a This combining of an assignment with another operator works with modulo and bitwrse operators (70, >>, <<, 6.' l, and ^) aswell as the arithmetic operators (+, -, *, and D, as shown a =3; b&=2; c ^= 5; //a=aoR3 //b=baND2 // c = c exclusiwely PORTC &= 3; // Itrite // // ANDed with all or thc // and the leavins O R e a Iw i t h 5 current value on PORTC 3 back to port c. Förcing cx.cpr lrF ro^4 2 .o bils the lower 2 bits 0 udaffected. I,6.4 THE CONDITIONAL EXPRESSION The conditional arpression is probably the most cryptic and inftequendy used ofthe operators. It was de6nitely invented to savegping time, but in general, it is not easyfor begrnning programmen to follow. The conditional arpression is covered here in the "Operators and Expressions" section due to its physical construction, but it is really more dosely asso ciated with control statements covered later in this chapter (Section 1.7, "Control State ments"). If the control sequence if (explession A) expressroa B; expression_C; is reducedto a conditionaler?ression,it readsasfollows: 6xp-ess.on A ., -xpr-ssion B : exprFssion.; l7 l8 In either of the forms shown above,the logical ergression eryress;on-Ais evaluated: If the result is TRUE, then erTre"rizz B is exccuted; otherwise, ex2ression_Cis exeuted. In a program, a conditional expressionmight be written as follows: (x < 5) = 1 ? y : y = 0; // if x is tess than 5, then //y=1,e1sey=0 I.6.5 OPERATORPRECEDENCE When multiple arpressions are in a single statement, the operator prccedence establishes the order in which expressionsare er,zluatcd by the compiler. In all casesofassignments and expressions,the precedence,or ordcr ofpdoriry must be renembered. When in doubt, you should either nest the expressions with parentheses-to gnarantee the order of process or look up the precedence for the operator in question. Some of the operators listed previously actually share an equal level ofprecedence. Table 1-10 shows the operators, thcir precedence,and the order in which they are processed(left to right or right to lettl. This processingordcr is calledgroupLngor association. 1(Hish) 2 0.u' ßinary l 4 "/% Shift 5 !- (rwe)"&++ Leli to Right sizeof Risht to Left Left ro Right Left ro Right Lcft to Right Equali{ 7 L!it to RrsL't & BiMi\e Left to Right Bitvise 9 Left to Risht Bihvise 10 Left to Right Logi.al l1 L%ical t2 13 14 0@) Table l-10 && Left to Right Leir r. Righr Right ro Lcft : +: -=/=r=%= <<=,,= &; ^= l= R sht to Leit Operotor Precedence Some operators in the table are coveredlater in this chapter in the "Pointen and Arrays" and "Structures and Unions" sections (Section 1.9 and Section 1.10) . These would include the primary operators like dot (.), bracket ([]), and indnection ( >), which are used to indicate the specificsofan identfier, such as an array or structure element, aswell aspointer and indirection unary operators, such as contents of (.) and address-of(&). Some aranples will Enbedd.d C LangLage Tutatial help to make this dear: 4i tl\|ould //1n * 4; y = (3 + 2) y jip y //wou1d //hisher - ll be.dusp anal woulal rha be done s - S.-- before . the yietal y = 20 because rhe O are rhe prioricy and force rhe + to be done / /wanld //highesr / /fi'rsL = 4 >> 2 * 3; d precedence = 4 >> 6 because Ehe * is priority risht than Ehe shift yietdy in / /operatsion y = 2 + 3 >> 4i y = 6 >> 4 alue to / /wöDld. yietd + operator the precedence of //the The precedenceof operators forces the use of a rule similar to the one for casting: If in doubt, use many parenthesesto ensure that the math will be accomplished in the desired order Extra parenthesesdo not increasethe code size and do increaseits rcadability and the likelihood thar ir will correcllyaccomplishiß mission. I.7 CONTROL STATEMENTS Control statementsare used to control the flow ofexecution ofa program. iflelse statements are used to steer or bünch the operation in one oftwo directions- while, do/while, and for statements ar€ used to control the repetition of a block of inst$ctions. switch-/cäsestatements are used to allow a single decision to direct the flow of the program to one of many possible blocks ofinstructions in a clean and concise fashion. t . 7 .I w H t L E L O O P The while loop appear early in the descriptions of C language programming. It is one of the most basic control elements.The format ofthe while statement is as follows: while (expression) while ( expression) statenent; statenenlt; slatenenL2; ] When the execution ofthe program enters the top ofthe uhile loop, the arpression is evaluated. Ifthe result ofthe expression is TRUE (non-zero), tl€n tlle statements within the while loop are executed.The "loop' associatedwith the while statement are those lines of code contained withifl the braces fl following the while statement, or, in the caseof a single statement wbile loop, the statement following the while statement. When erecution reach€sthe bottom of the loop, the program flow is returned to the top of the while 1oop, where the e4ression is tested again. Whenever the expression is TRUE, the loop is e-{ecuted. Whenever the er?ression is FAISE, the loop is completely bypassedand c{ecution t9 20 continues at the tust strtement following the while loop. Consider the following: <stdio.h> +include void nain (void) t char c; // if c less td\n", (inE)c); // // than 100 then // print c's vaLue each tine lhrouqh the Loöp increnent c J Edd öf while (1) // prosran si.ra I that rhe // indicace / /Etosra is f i nt shed is dlwdvs TRUE, rlea .uc- . ir n6!p, \n"); l In this example, r is initialized to 0 and the text süing "Stan of program" is pnnted. The while loop will then be arecuted, printing the value of r each pass as r is incremented ftom 0 to 100. When r reaches100, it is no longer less than 100 and the while loop is bypassed. The "End of program" tevt string is printed and the program then sits forever in the zahilell) statement. The functioning ofthe zal;/rft) shtement should now be appareot. Since the "1" is the ax pression to be evaluated and is a comtant (1 is always non-zero and thercfore considered to be TRUE), the while loop, even a loop with no instructions as in the example above,is entered and is never left becausethe 1 always eraluates to TRUE.In this case,the uh;le(I) ß used to stop execution by infnitely executing the loop so that the processordoes not keep executing non existent code beyond the program. Also note the cast of c t o zn integer tnslde t\e Finf) 6mction, inside the while loop. This is necessarybecausethe ?r;ntf) fnrrcnon n nost embedded C compilers will handle only integer-size variables conecdy. The while loop cal also be used to wait for an event to occur on a parallel port. void main (voidl while : (PINA & 0x02) //hanss he.e Fairinq po! //se.ondblof vhile (1) // since 1is while rhe A js lqh always TRUE, then jusr siE here,. Enbedded C La,E"nge TLtatir/ In this example, the while loop is used to await a bit going low. The e'pression being eval uted is "PINA A 0x02", which will mask all but the secondbit (bit 1) of the data read from port A. While the bit is at logic 1, the result will be nonzero (TRIIE), and so the program will remain in the while loop until the r,alueon the secondbit drops to zero. At a later point, it should become clear that in real-time programming this construction is not appropriate, but it is a correct use ofa while statement. t.7.2 DO/WHtLE LOOP The do/while loop is very much like the while loop, except that the expressionis tested afrer the loop hasbeen executedone time. This meansthat th€ instmctions in a do/while loop are always executed ozcebefore the test is made to determhe whether or not to remain in the loop. In the while consttuct, the test-ß mrde beforethe instructions in the loop are executed even once.The format ofthe do/while statement is as follows: do { stsalementl; statene4ts2; ) whrle lexpressioa) while (expression), ; When execution reachesthe bottom ofthe dolwfiile consmrct, the expressionis elduated. If the result ofthe expressionis TRIJE (non-zero), then the program fow is returned to the top of the do/while loop. Each time execution reachesthe bottom of the construct, the expression is tested again. Whenever the ergression is TRIJE, the loop is executed,but if the expressionis FAISE, the program continues on with the instructions that follow the construct. The previous example,coded using the do/wfüle construct, would appear as follolr,s: <stdio-h> +include void nain (woid) I p.intf{" start of proqran \n"); { ) rhile (c < 100); printf(" Enal of pioqrtu \n'); // // increnent if c less // inalicate / /prosram c than that is 100 then the finished zl n / / since I is .lvdys IRUE, rnen lus- î- n-.-. l In tiis e\ample, r is initialized to 0 and the text string "Start of program" is printed. The do/while loop will then be executed, printing the value ofr each pass as r is incremented from 0 to 100. When r reaches100, it is no longer less than 100 and the do/while loop is blpassed. The "End ofprcgrarri text stdng is pinted, and the program then sits forever in t|.e ubileft ) statement. 1.7.3 FOR LOOP A for loop construct is g?ically used to execute a statement or a statement block a specifc number oftimes. A for loop can be described as an initialization, a test, and an action that leads to the satisfaction of that test. The format ofthe for toop statement is as follows: för (expr1; expr2; exprS ) { statementl; sLatenenl2; l ax2r7 will be e"xecutedonly one time at the entry of the for loop. ?r1,"J is typically an assignment statement that can be used to initialize the conditions for dr1,.2. exPr2rs a condi tional control statement that is used to determine when to remain in the for loop. expr3 is another assignment that can be used to satisfy the ex?r2 conCntion. When the axecution ofthe program enten the top ofthe for 1oop,e1pr7 is execüted.ej.Pr2 is evaluated and if the result of qP,'2 is TRUE (non-ze ro), then the statements within the for loop are executed-the program staysin the loop- lvhen €xecution reachesthe bottom of the construct, ,rp3 is executed, ,rrd the program flow is retuned to the top of th€ for Ioop, where the rx2r2 erpression is tested again.Vvhenever ,{pr2 is TRUE, the loop is executed. Whenever e*2r2 is FALSE, the loop is completely bypassed.The for loop structure could be representedwith a while loop in this fashion: white ( expr2 ) slaLenentl; stsa!enen!2; exprr; ) Here is an etample: +include <stdio.h> void nain (void) Eßbedled p, :nr for(c l' s orl or proqrdm = 0r c < 100; c++) \n") i // if c less C Lahgrage Tutatidl 100 then than .. I p td\n',(;n_).t; j prin-t{ L cl o. whtle(1) // proq'dm since 1is \r",i p-int // / / c's the loop rhrouqh before c++ is executed // indi_dra // flnished // always rhdr TRUE, then jus! the Fnp o oo em sit s here.. J In this example,the tet string "Start ofprograrri is printed. ris then initialized to 0 within the for loop construct. The for loop will then be executed,printing the value of c each pass as r is incremented from 0 to 100, also within the for loop construct. When r rcaches100, it The "End ofprogram'text string is is no longer lessthan 100 and the for loop is bypassed. printed, and the program then sits forever in the ubile(l) statement. t.7.4 tF/ELSE iflelse statements are used to steer or brrnch th€ operation of the program based on the evnluation of a conditional statement. IfStatement An ifstatement has the following form: i' erp -Fss 01) { iflexpressior) statenent; statenentt; statenent2; l If the expression result is TRUE (nonzero), then the statement or block of statements r executed. Otherwise, if the result of the ergression is FALSE, then the statement or block of statementsis skipped. IflElse Statement An i9else 'raremenrhasthe following form: if (expression) ir (expression) slaLenentl; I siatementl; else 23 24 statement2; l 1, statenentsf; siatenents4; ] The else statement adds the specific feature to the progräm flow thar the statement or block oF statements associated with the else will be executed only if the e\prcssion result rs FALSE. The block ofstatements will be skipped if the exTressionresult is TRUE. An else statement must alwals follow the ifstatement it is associatedwith. A common programming technique is to cascadeigelse statements to create a selection if (expr1) statenentt,. else if (expr2) statenent2,. e l s e i f ( e x p r 3) slatenenl3; statenent4,. This sequence of ilTelse staternents will select and execute only one statement. If the 6rst e..pression, cr1,'7, is'fRllE, thell statenentl will be executed and the remainder of the statementswill be blpassed.Ifeqprl is FALSE, then the next statement,if kryr2), wlllbe eyecuted.If rrPr2 is TRUE , t\et statenent2wilbe executedand the remainderblpassed, andso o::-.lf er.?rl,ex?r2,arrde1pz3areall FALSE,rheß statennt4 wlTbe exectted. Here is an exampleofi9else operation: <stdio,h> +incLude void main (void) prinlf( for(c Saart = 0; of prosran c < 100; c++) \n // ); while c is less than 100 then .. { erse .-11 o' 'tI("0 // use ialelse ro snow rn6 "); >32) && (c < 661) // nubers if((c thar c is in '); prinrf ("33<c<66 räi96 ot Enbedded.C Ldngeag. TLtüia/ 25 , ( "66<c<100 '); f { i.- !o\a",(irl).); p!urf p".. /1print //through r' the toop ] princf{" End of while(1) Lhat the proqran is finished \d ); // indicate here.. 1 ls always TRUE, then jusE sit proqre // since In this erample, the text string'Start ofprograrri is printed. r is then initialized to 0 withn the for loop construct. The for loop will then be executed,printing the value of r each pass as r is incremented from 0 to 100, also within the for loop construct. Ifthe value of r is less than 33, then the text string "0<c<33" is printed. If the value of r is between32 and 65, the text sting "33<c<66"is printed.Ifthe valueofr is not within either of the preceding cases,the text sfting "66<c<10f is pdntedWhen r reaches100, it is no longer less than 100 and the for loop is bypassed.The "End of program' te),1string is printed, and tie proglaln then sits forever in the z'Zi/e(1) st^temet\t. Using the constructs and other techniques covered so far, it is possible to create a prcgram that efficiendy tests each bit of an input port and prints a messageto tell the state of the bit. <r,IEGA8535.h> +include definition // resj,sLet an atnel aTl{8GA8535 // woid file for nain (void) { unsisned bit_nask för char = Ii cnt, bit nask; //variables bit wiEh lowest //srart (cnL=o;cnt<8;cnt++) //for loop to test 8 bits { if beloa test port birs // the instructions result // and print (cest polt & biE nask) prinLf( BiL Sd is hiqh.\n", (int)cnt); plintf bit_näsk wl-i_erlt //sin.p ( Bit <<= Ii is gd is //slrifL älwdy- 1 o w .\ n " , ( i n t ) c n t ) bit fRLE, ao be Lhe- ; tesred üsr - ."---.. 26 The exampleaboveusesa for loop that is set to loop eight times, once for eachbit to be tested. -fhe tnri^ble bit_rnaskst^rts at a value of 1 and is used to mask all of the bits except the one being tested.After being used as a mas( it is shifted one bit to the left, using the compound notation, to test the ner(tbit during the next passthrough the for loop. During each1oop,the i9else construct is used to print the conect statement for each bit. The conditional statement in the ifconstruct is a bitwise AND usiog &l_rtarr6 to mask unwanted bits during the test. Conditional Expression Another version of the i9else is the conditional expression,designed to savethe program mer time and stepsthrcugh a simplfied syntar. The iflelse sequence if{expression a) statenentl t statenent2; can be reduced to a conditional erpression that would read as follows: F:p ess:oa_A ? srdtementl : sfatemFnl2; In both ofthe forms shown above, the logical erpressjo'J erpression Ais evÄuated and ifthe rcsult is TRUE, then tatementl ts exeüteÄ; ot]retwise, ttatement2 is exec-rted. In a program, a conditional expression might be wrinen as follows: 'c 5l ? y t : y - 0; // if x's less Lhaa ), //y=1,e1sey=0 -hen t.7.5 SWTTCH/CASE The switch/case statement is used to execute a statement, or a group ofstatements, by the value ofan egression. The fom ofthis statement is as follows: (expression) ssltch I case constl: statenentl; stalenent2; case const2: staLenent3; statenent4; case constx: statenent5; staLenent6; defaulL: statenencT; stsatenent8,. ) selected Enbedded C Language Tttarial ^fhe expre:sionis evaluated and its v3lue is then compared against the constants (.rn$-l, nnst2, . . . constx\.Execrtton begins at the statement following the constant that matches the value of the expression.The constants must be integer or character !"lues. All of the statements following the matching constant will be e<ecuted,to the end ofthe switch construct. Since th; is not normally the desired operation, break statements can be used at the 'fall-ttuough" of execution and allow the proend of each block of statements to stop the gram flow to resume after the srvitch construct The default caseis optional, but it allows for statementsthat need to be executedwhen there are no matching constants. +incLude <stdio.h> +include <MEGA8535.h> reqisLer alefinition header aTMEGA8535 // an atnel . // file for nain (voidl void { unsigned char c; t = PrNA & oxfi swirch (c l c // tead the 10wer nibble of port a I case case case case case '0' : '1': // you can have nultiple '2': // Eor a '3' : prinLf(" bteaki 's': printf{" seE of cases statements.. c is a nunber less than 4 \n"); // break Eo skip out of the Loop one is ok., // o! just c is a 5 \n'); c is 4 or break; defautt: prinhf(" is > 5 \n'); j ) J This program readsthe ralue on port A änd nasks the upper four bits. It comparesthe ralue ofthe lower nibble from pon A against the constants in the casestatement.Ifthe charäcter is a 0,1,2, or 3, the text string"c is a r mber lessthan 4: will be printed to the standard out put. If the character is a 5, the text string "c is a 5" will be printed to the standard output. If the characteris none ofthese (a 4 or a nümber greater than 5), the default statementswill be executedand the texl string "c is 4 or is > 5" will be printed. Once the appropriate cäsestate ments have been executed,the program will retum to th€ top ofthe li,hile loop and repeat 27 2A I.7.6 BREAK,CONTINUE.AND GOTO The break, continue, and goto statements are used to modi! while, do/while, and switch statements. the execution of the for, Break The break statement is used to exit fiom a for, while, dolwhile, or switch statement. If th€ statements ,re nested one inside the other, the break statement will exit only from the im mediateblock of statements. The following progam will print the value of r to the standard output as it is continuously incremcnted from 0 to 100, then reinitirlized to 0. In the inner while loop, . is incremented until it reaches100, and then the break statement is execut€d.The break statement causcs the progrnm execution to exit the inner *füle loop and continue execution of the outer while loop. In the outer while loop, c is set to 0, and control is returned to the inner while loop. This processcontinues to repeat itselffor€ver. +include <stdio-h> void nainlvoid) I I { (c > 100) if bteak; // Ehis wilt take // b1ock, ctearins printf ( 'c = sd\n" , c) ; us out c.. of this while ) // // clear c and then things witl besin asain printinq the vatues 0-100, 0-100, etc.. ) Continue The continue statement will allow the program to start the next iteration of a while, do/while, or for loop. The continue statement is like the break statement in that both stop the execution ofthe loop statements at lhat point. The difference is that the continue stat€ment starts the loop again, ftom the top, where brcak exits the loop entirely. +tncLude void <stdio. main (void) whi te (1) h> Entedded C Ldngtdge Tttaridl white{1) t if (c > 100) continue; p.intf{"c // This will // stop when c>100, // continue // this = *d\n',c); cause will loop // to because cause t'e printins ihe the skipped! no code afEer / /witt the to Ehe rest of ! continue be execuEed J In this arample, the ralue ofc will be displayed until it reach€s100. The program will appear at this point as if it has stopped, when in fact, it is still running. It is simply skipping the insement andPn'ztf, $atements. Goto The goto statem€nt is used to literally "jump' e<ecution ofthe program to a label marking the ne).1statement to be executed.This statement is very unsmrctured and is aggravating to the 'puist," but in an embedded system it cän be a very good way to sale some coding and the memory usagethat goeswith it. The label can be bdore or after the goto statement in a function. The form ofthe goto statement is as follows: soto identi fief,; identifier: sLatenenl,. identifier: statenenc; qoto The label is a valid C name or identifer, followed by a colon O. +include <stdio.h> void main (woid) t whi le (1) { identifier; 29 30 { if {d == c) goLo start d = c; (c > 100) if continue, asrain; // aI witl (sEuck? bait out | ) // renenbe! where we rere // this ui11 reinitiate this loop // while be checked to see if // d witl c is sruck I)rintsf {"c = Sd\n", c) ; // because c won't chanqe { > 1001!) ) In this etample, r and / are initialized to different va\xs.The if (d == ) statement checLs the values and, aslong asthey are not equal er<ecutionfafls tirough to the assignment / = r. If r is less than or equal to 100, cxecution falls through to the incr€ment . statement. The rdue of r is printed and the while loop begins agäin. The values of c and / will continue to differ by 1 until c becomes greater than 100. With r at a välue of 101, the continue state ment 1vill causethe incre ment eNÄ printJ, stztementsto be skipped.Th e tf (d==t) w1l,become TRUE, since they are now equal, and the goto will causethe program execution to jrmptothe start again label. The result would be the value of r printing from 0 to 100, over and over agarn. Chapter I Example Proiece PartA This is the fust portion ofa project that witl be used to demonstrate some of the concepts presentedherein Chapter 1-This exampleprojectwill be basedon a simplegame accord ing to the following situation: You have been asked to build a Pocket Slot Machine as a mid-semester project by your favorite instructor, who gave you some basic specifications that indude the following: | . The pressandreleaseof a butronwill be the "pullingthe arm of the One-Armed BandiC' 2. The durationofthe pressandth€ releasecanbe usedto generarea pseudo-random numberto createthreecolumnsof figures. 3. A flashinS lightis usedto indicatethe machineis"movingi' 4. Therearefour kindsof figuresthat canappearin a column: a. Bar b. Bell d. Cherry Ehbedded C Lang"dge'I"taridl 5. The payoutof the machinehis the followingrules: a. Threeofa kindpaysa Nickel. b. A Ch€rryanywh€repaysa Dime c. ThreeCherriesareajackpor d. Everything €lseloses. In this first step we will develop a briefprogram that touches on severalofthe concepts.We will develop a nain) that contains vadous t'p€s ofcontrol statements to create the desired opemtion. This fißt passwill get the press and release,work up a pseudo random number, and print the results in a numeric form using standard VO tunctions. while, do/while, and for loops will be demonstrated aswell as iyelse control statements. slo, // !.ä.hin-' -- Tfc Mini Excr.ise Phase 1.. // <r4EcA8515.h> +include *dpfinÄ x-ol 4000000L +detine baud 9600 // Global void 'i processor /* specific .r-qu-n.! /'qud-tz.rystäl /* Baud rate "z */ Variable Declarations. , s t , s e c o n d , L 1 i ! c l; , / . o l u m n s i n r h F s . o // nunbe! to // // hirialize porL A all */ infornation fo.n mä n na a seed for nain (void) t PORTA = OXFF; DDRA = 0x00; PORTB= 0x00; DDRB = 0x02; // // // 7Li-Eialize lhe UARI conllol regisrer Rx & Tx enabled, a dara t'irs UCSRB=0x18; initialize the UART'S baud UBRRT=xra1 /16lbauaI-1 ; while (1) / / do raEe foreeer. . Lhe r/o inpurs , porrs random 3l 32 while firsE { I ( PINA.0 ) = second wait för a button anal tet the counter ro11 ove! otet Lö forn a seed. // // // = third // ^= seed>>l; first sA-ond - seed 2; ^= seed>>3; third seed++; 'e(PINA.0 -- 0): "l for{count = 0; // // // // counts . 5; = seed; preload // and the cotunns while wäil n9 fo, b-.-on !e_eq-e, Exclusiwe oRing in the movinq seed cdn really s-i up he ru bers, keep wni le rolling öwer the seed paEtern Fhe bur Lon is press-d eounr++) // - l1-sh sh h e done. 1 fo. (detay = 0; delay < 10000; detay++) PORTB.I = 0, = 0; for (detay alelay // rurn < 10000; the LED on.. delay++) PORTB.I = 1; // Luln the LED off. J first &= 3; prinEf(' // linit nunber to watues ftom 0 to 3 // shos Ehe values. . -> Sd. gal ,gd < \n', firsr, second, third), // deternine a payour. . == 3) && (secon(I == 3l && (rhird == 3)) if((firsr printf("Paid out: JÄc(PoT!!\. );// Thlee 'cherries' == 3) ll {second == l) ll (rh1!d == 3)) else if((first plintf("Paid oüt: one Dine\D ); // One 'Cherry' == second) && (second == rhird)) else if((first plintf('Paid out: one Nickel\n ); // Three of a kind plinrf("Paid oul: zERo\n.); // Loser.. Enbedded C Language T,tarial I.A FUNCTIONS A function is an encapsulation ofa block ofstatements that can be used more than once m a program. Some languages refer to functions as subroutines or procedures. Functions are generally written to break up the operxtional elements ofa program into its fundamental parts. This allor* a programmer to debg each element and then use that element agarn ancl agam. One of the prirne advantages in using functions is the development of a "library" As functions are developed drat perform a certain task, they can be saved and used later by a different application or even a different programmer This saves time and maintams stability, since the functions devdoped get used and reused,tested and retested. A tunction may perform an isolated task requning no parameters whatsoever. A function may rccept pammeters in order to have guidame in performing its designed task. A function may not only accept parameteß but retum r value aswell. Even though a function may accept multiple parameten, it can only retum one. Some c<amplesare as follows: p. -Lf/il! s // this // wiLlr is // performs function p a r a m e t ers, no in ä pdrdmeL.r gd',x); printr ei11 pr in' ils a 1 second or outs de1ay, pdrdm6r pis c = serchar o ; // // getchar will return standard input a vatue fron the The standard form ofa function is t s y p e f u n c t i o n _ n a m e ( E 1 4 ) ep a r a m l . { statementl; stsatsements2; type param2, .,, ) statementx; ) which is a gpe, followed by a name, followri by the primary operator //. The parentheses, or tunction operator, indicate to the compiler that the name is to be executed as a tunction. The gpe of a function or its parameterscanbe anyralid variabletype suchasint, char, or foat. The gpe canalsobe emptyor void.The typevoid is a valid gpe and is usedindicate a panmeter or retnrnedvÄueol zerosize.'['trcdef:lft g?e ofa function is int. So a qpical tunction dedarationmight be asfotlows: unsigned char getchar (woial) t while( (ucsRA & 0x80) == 0) 33 34 // ; '-l -' UDP; // / / wait for a character to arrive return jrs uns gnad -t,a calleL J h this example,getcbar) is a function thd rcquires no prrameters and rcturns an unsigned chuacter value when it has completed execution.^l|l'e getchar) fnr,ction is one of the many library functions provided in the C compiler These functions are availnble for the programmer's use and will be discussedin more depth later I.8.I PROTOTYPINGAND FUNCTION ORGANIZATION Just as in the use ofvariables and constants, the function try€ and the types ofits parame terc must be declared before it is called. This can be accompJishedin a couple ofways: One is the order ofthe declarations ofthe functions. arrd the other is the use of {irnction protoq?es. Ordering the tunctions is always a good idea. It allows th€ compiler to have all the infor mation about the function in place before it is used.This would also mean that all prcgrams would have the following format: r:ables rnL aarl, var2, wou d be l:sL !at3; // decLarations int func!ion1(int of functions x, int y) woutal cone nexr { ] void function2 (void) l // main woutd be builE void nain (void) last l var3 = functionl () ; function2 (va!I, ear2); j This is all nice and orderly, but it is also sometimes irnpossible. There are many occasions when tunctions use one another to accomplish a task and you simply cannot declare them in such a way that they are all in a top-down order. Function protoqpes are used to allow the compiler to know the requirements and the gpe ofthe function before it is actually declared, reducing the need for a top-down order The previous example can be organized diferendy: int varl, va!2, war3, // aleclalatio. of globat wariables Enbedded C La"EudEe Tutarial void main (void) // nain t // these fuDctions ale // conpiler var3 = funclionl (vat1, noi yet known ro ihe var2); function2 O,. ) // declalations of // Fuacrion Redefrned funcrions here now generate a E!!or" I I void funcrion2 (woid) This organization would g?ically lead to an error messagefrom the compiler. The compiler simply would not have enough information about the functions that are calledin nain), or their format, and would be unable to generate the proper code.The protogpes ofthe tuoc tions can be added to the top of the code like this: of // the prototl@e (int, int functionl void int function2 vart, var2, a function int) , te11s the conpiler what tö expect (vo ial) ; var3; vo) o ndin(voio) // declaiation t/ ndin of qlobal variabLes { var3 = funcbionl(vat1, function2 ( ) ; !at2) t J OK, since // lhe declaraLion of lhe funcrions here is perfectty // the folmac of rhe funcLions are presenred in the plototypes int functionl(inL x, inL y) J void function2 (void) The compilernowhasall therequiredinformationabouteachfunctionasitprccesses thefunction name.As long asthe actualdedaredfrrnctionm cherthe protot1pe,er"erythingis 6oe. 35 36 The C compiler provides many library functions. They are made ardlable to the progam by th. "#;ndude .fhnana.rl>" statement, where flerune.b w be the file containing the tunction protogpes for the Iibrary irnaions. In previous e'€mples, we used the tunction ?rintfq. The PrinlJü tnnction itself is declared clsewher€, but its protogpe arists in the stdio.h header fle. This allo*s the programmer to sirnply indude the header fr1eat the top ofthe program and start w:iting code.Thc library functions are eachdeEnedin Appendü ^, "Library Functions Reference." I.8.2 FUNCTIONSTHAT RETURNYALUES In many cases,a function is designed to perform a task arrd return a value or status from the task performed- The control word rctum is used to irdicäte an exit point in a function or, in the caseofa non-void g?e fnnction, to select the value that is to be returned to the caIler. In a tunction of gpe void, int zj void sun{int z = x // qloba1 variable x, int y) + y; // z is z nodified by rhe function, suno ] the retum is implied and is at the end of the function- If a return were placed in the void tunction, like this, void sum(int t // // y; this woulal reEurn .orhing,. and. this sould be skippea ) the return statement would send the program execution back to the caller, and the statements following the retu.n would not be executed. In a function whose gpc is not void, the return control word will also send the execution back to the caller In addition, the return will place the value ofthe expression,to the dght of the retum, on the stack in the form ofthe gpe specified in the dedaration of the tunction. The following tunction is ofgpe foat. So a float will be placed on the stackwhen the float cube{f1oat return w) (v*vtw); // rhis returns a type float value j The ability to return a value allows a function to be used as part ofan expression,such as an assignment. For example, in the program below, void main (woid) EtubeddedC Ldagtage Trtarial b = 3.14159; // put Pr inro b a = cube(t,) ; // // pass b Lo lhe cubed function, assiqn irs return value ro a prinl !r"a tl, b gr and -s._ irt.1. \n",c,b) while(1) ) a would be assignedthe ralue ofthe function czre(/. Thc result would appear as a = 3 1 . 0 0 6 1 9 8 ,b = 3 , 1 4 1 5 9 t.8.3 RECURSTON A recunive tunction is one that calls itself The abiJity to generate recunive code is one of the more poweitul aspectsof the C language.When a lirnction is calted, its local variables are placed on a stack or heap-space,along with the addressof the caller, so that it knows how to get baclc Each time the finction is catled, these allocations are made once again. 'teentrant" since the values from the previous call would be left This makes the function within the previous allocations, untouchedThe most common example ofa recursive operation is calculating factorials. A factorial ofa number is the product ofthat number and all ofthe numben that lead up to it. Fof example, 5r - 5 , 4 12 This can be stated algebraically as *(n2)+...*2+r n'=n*(n1) o! nt=nr(n1) So a prograrn to denonstrate this opemtion might look like this: + include int <stdio.11> fact (int n) if (n == 0) : ieturn l (n * facL(n-1)); // n // definition is 7ero, tal u'- of // otherwise, //n // lunLitn= leturn n * the // call to d on_, br/ factorial call nyself nyself 0, wlth rhen results lhe | 37 38 void nain (void) n t..trq); prinrf( vhile // 5! = Sd \n', conpule 1!, n); ( 1) re.u s'/c1l // prinr // aone the resuLt When the tunctionlrzfl is called with argument z, it calls itself z-1 times. Each time it calls itselfit reduces z by 1. \4then z equals 0, the tunction returns instead ofcalling itsetf again. This causesa "chain reaction" or "domino effect" of r€tums, which leads back to the call made in nainQ, where the result is pdnt€d. As powerful as recursion can be to perform factorials, quick sorrs, and linked list searches, it is a memory consuming operation. Each time the function calls itself, it allocates mem ory for the local variables ofthe function, the retum value, the retrun addrcssfor the func tion, and any parameters that are passedduring the call- In the previous e<xmple,this would include the following: -(o"ssed p-lampFer) inl Retsuln value Relu.n address 2 byLes 2 byres 2 byres 6 bytes, per recurslön, nininun, In the caseof"5!", at &art a total of 30 bltes of memory would be allocated during the lac torial operation and deallocatedupon its retum. This makesthis type ofoperation dangerous and impnctical for a small microcontroller If the depth of the allocation due to recursion becomestoo great, the stack or heap-spacewill overflow, and the program's operation will become unpredictable. Chapter I Example Proiece Part B In this phase of the dwelopment ofthe Pocket Slot Machine, we are going to create a cou ple of functions to break up the main loop into smaller chunl<sof code aod make the code slighdy more readable.The pans ofcode that flash the lights and compute payout wil be moved into lirnctions, shotteningthe nain) fünction and maling it a bit easier to follow. AJso, a switcVcase statement will be used in the indication ofpayout. // // "sLot Machine The üini-Exerclse Phase 2.- +inct!de rv[cA8cl5.]- /. pro.essor spp.'. i. into!norion . Enbedded C La"g"age +define xtal +define baud 9600 +include // clobal 4000000L <stdio -h> quartz /* Baual laEe /' rhis variable Declaralions. first,second,thiral; // +define DrME 2 +define zERo 0 void /* flash n. // // a variabte delay reaalable // = 0; delay PORTB.l = 0; = 0; fo.(delay delay PORTB.I = t; for slot to ftash tt) /1 < 10000; // just // turn < 10000,. // liqhrs a for payoutss code nunber 'i9h tldsh random lime differenl nake rhe */ hunans. the ion nachine alefines siwe in order to .ount fo! (de1ay o- a seed n) 1iqht6(char (hp p' irLl{) qets */ [Hz] . in the colunns nunber Eo forn This ndes /t /t /t frequency crystal '/ ^ mole tines c do' aletay++) count up and sait Lhe LED on., detay++) I inl qeE-payout (void) I -- ))) ll ö.& {thi'd iI((_i sr -- 1l [3 (sF.ond -relurn JACKPOT; // if at1 "cherries'.. == 3) ) == 3) | | (second =- 3) | | (third eLse if( (fi.st return DII4E; any ale cherries".. // it -- sA.ond) rd (second -- !hi,d)l ((li-sr else void return NICKEL; reLurn ZERO; // // if three orhervise are alike, of any you lose nain (void) t locat valiabte for */ */ of Ehe LED off.. turn Tutoriat kind, 39 40 // IniLi,aaize potL a att // potL // 8.1 the 1/O polrs inputs is (1iqht) an output DDRB = 0x02; // // IniLialize the UART conrrol reqlster Rx & Tx enableal, 8 data Irits UCSRB=0x18; // ibiLialize the UART s baud UBRRL=Xra1 /16lbaud-1 ; ( 1) whtte white{PINA.0) seed++; firs! // <to toteter.. // Wait. fot a button and 1e! rhe counter rotl ower over to fom a seed. // // = second rate = bhi.d = seeal; // preload tbe and colunns do // Mix tp the aumbers / / while waiEinq for tutton release. ^= seed>>1,. // Exclusiwe first ORing ln the noving seed second^= seed>>2,. // can rea1,1,y stir up the mnbers. ^= seed>>3; lhird seed++; // Keep rollins ower the seed pattern == 0l; // rhile the button is pressed. ) while(plNA.o | flash_]ishts15); first &= 3; printf('--> flash // // 3d, 8d, liniL = ger_payout switch(i) nuiber lishts to 5 Eines,. walues flon // show the walues. . 3d < first, \n", second, // i the deternine a payout. o ; // oos priot Lhe payoDt resulrs t ZERO: plintf ('Paid ouE: zERO\n') ; b'!eak; NICKEL: princf ( "Paid out: One Nickel\n ')t . 0 ro Ehiral); 3 Enbed.led C Ldag"age Tutarial p . f("Ddid our : one Dima\n"); JACKPOT: ("Paid ouL: printf I.9 POINTERS AND J A C K P o T !! \ n ' ) ; ARRAYS Pointers and arays are widely used in the C language becausethey allow programs to perform more generalized and more efficient operatiors. Operations that rcquire gathering data may use these methods to casily accessand manipulate the data without moving the data around in nenory They also allow for the grouping of associatcdvariables such as communications buffers and character strings. t . 9 .I P O T N T E R S Pointers are variables that contin the ad&ess or location of a variable, constant, function, or data object. A variable is declared to be a pointer with the indircction or dereferencing operator(*): // p // fp a pointe! i,s a pointer is Lo a character Eo an inteser The pointer data q?e ällocates an area in memory large enough to hold the machine addressof the variable. For e"umple, the addressof a mcmory location in a gpical microcontroller will be described in 16 bits. So in a typical microcontroller, a pointer to a chamcter will be a 16 bit ralue, even though the character itselfis only an 8-bit value. Once a pointer is declared,you are now dealing with the addressofthe variable it is pointine to, not the value of the variable itsell You must think in terms oflocations and contents oflocations. The addressoperator (&) is used to gain accessto the addressofa variable.This addressmay be assigned to the pointer and is the pointer's value. The indirection or dereferencing operator (*) is used to gain accessto the data located at the addresscontained in the pointer. For example, // to a character a pointer a aa.l b are characLers // p // p is is now poinrinq Eo a In this example,2is assignedthe addressofa, so/ is "pointing to" r. To get to the value of the wriablc that is poirted to byp the indircction operator (.) rc used.When axecuted, the indirection operator causesthe value of2, an address,to be used to look up a locätion in memory The value at this location is then read from or written to 42 according to the expressioncontaidng the indirection operator So, in the following code, *2 '.ould causethe value located at the addresscontained inl to be rcad and assignedto l. // b pquols .o poinr-d l!F.onrpnrs p b! Therefore, the combincd code of the previous two examples would produce the same The indirection operator can also appear on the right side ofan assignment. In this example, *p; char char a, *p b; - b; // // // // p is a pointer co a aad b a.e characte.s the poinceal localion assigned the value of to by p It is the memory location, at the addrcss stored in 1 is assigned the value of /. This wor d produc€ the sameresult as \\lhenever you read these operations, try to read them as "/ is assignedthe value pointed to byf'and ! is assigned the addressofa" This helps to avoid making the most common mistake with pointers: b = pi // // b will be assisneal a walue p pointss to not rhat p = a, // p witl be assiqneal the value of p, of an address, a, not its address These two assignments are allowed because they are s1'nuctically corect. Semantically spealing, they are most likely not what was intended. With power and simplicity comes the opportunity to make simple and powerful mistakes. Pointer nanipulation is one ofthe leading causesofprogramming misfortune. But exercising a litde care,and reading the syntax aloud, can greatly rcduce the dsk ofchanging memory in an unintended fashion. Pointers are also an excellent method ofaccessing a peripheral in a rystem, such as an I/O port. For instance, ifwe had an 8 bit parallel ougut port located at ü11010 in memory that port could be accessedthrough indirection as follows: drc oul port = 0a1010; rout Poll = oxaa; outJrolf os a po a out_polE wirh rhe address vatue //assisn //now assisn ou!_po.ts's address a value In this code,the location pohted, toby oütJ)ottwoüldbe assignedthe value 0xAA. It can also be described as 'any value zsslgßd to "oxu)ort vnll be written to memory address0x1010." Enbedded C Ldkgxage T"toridl Becauseofthe structure ofthe C language,it is possible to have pointers that point to pointers.In fact, there really is no limit to the depth ofthis gpe ofindnection, except fo{ the confusion that it may cause.For example, int *p1; / / pa is a pointer to an inteser ''' : r inL "a2: '..o,: i, p2 is pJ is // lo // tt // pl is assiqned thaL address of i p2 is now poinfing ro Lhp poin'e p3 is pointing to the pointer that // La i / / I}]erefore, j is assisned Ebe vatue poinLed to pointed rhe pointed ro a poinl-r, a poinrer, -o d po a(e ro .n o d po 1.e., Lo - inreSer poincer an integer i; &i; &p : &p2i j t/ ,/ = ***p3; // // to by value .o i is poinEinq by the by p3. value yields the sameresult as j = i; // any suestions?? Since pointers are effectively addrcsses,they offer the ability to move, copy, and change memory in all sorts of rvays with very litde instruction. When it comes to performing addressarithmetic, the C compiler makes surethat the proper addressis conputed basedon the t}?€ ofthe variable or constant being addressed.For example, inr *prr; lonef * lptr; // // lptr = lpLr + 1; -ovcs the pointer (2 byEes away) to //noves Ehe poinrer to // 14 byEes away) r he nöx- the next .. esc' lons inteqer ?t/ and l?tr arc iDcIemented by one location, which in realig is 2 bytes fot ?tr ^nd 4bttes for /24, becauseof their subsequenttypes.This is also mre when using increment and decrementoperations: // moves bhe pointer / / 12 bytes) // // nowes che pointer ioteqer locarion to the back to .exr lhe integer precedinq location lonq ( 4 byEes) Since the indirection f) and address(&) operators are unäry operators and are at the high est precedence,they will always have priority over the other operations in an expression. // 43 Since increment and decrement are also unary operators and share the same priority, arpr€ssionscontaining theseoperaton will be evaluatedleft to right. For example,listed below are pre-increment and post increment operations tlat are part ofan assignment. Pleasetake note of the comments in each line as to how the sameprecedencelevel affects the outcome of the operation: . .p-,; /1össi9n // -'__p; c - t' r.he increnent the vd.lua poinf-d.o address p -.r-mFrr .he cddrass p, poinled Eo by p b! fn6n p, äss 9. - - d . .- // value // // increnent ässiqn . pointed the value ro., edvinq fna assiqn vatue pointed ro by p, and then the walue poinEed to by p, leavinq of p untouched (ap)++; // // // Lo by p, /a1.6 o then p .r'o -l--o c the increnent the value Pointers can be used to extend the amount ofinformation retumed &on a function. Silce a function inlerendy carr rcturn only one it€m using the return control, passing pointers as parametersto a function allows the function an avenuefor retuming additional values.Consider the following tuncnon, sua?20: void swap2 ta, (in! int *b,) t int temp; tenp = *b; // place value pointed tö by b into temp *b = *a' // nove rhe value poinred ro by a inro location // pointsed ho by b. *a = temp; // // Now set the value value of tenp. of loeatiön a to the J This sample function swaps the values ofl variables it wishes to transposelike this: in! v1, v2; svap2( &v1, &v2); // pass and ,. The catler provides thc pointers to the the aaldresses of w1 and v2 S:nce t\e swap2) finction is using the addressesthat were passedto it, it swaps the val ues in variables and r,2 direcdy. This processofpassing pointcrs is frequently used and "1 can be found in standard library functions like xanfl). The vazl11 tunction (defned in Enbed.le.! C Lahgüage Ttturi4l stdio.h) allows multiple parameten to be gathered from the standard input in a formatted manner and storesthem in the specfied locations ofmemory- A typical c a11toseanlUlooks like this: int. x,y, z; scanf("3d 3d 8d', &x, &y, &z); 'lhis scanfl) caJJN; rctrieve three decimal integer values ftom the standard input and place these r-aluesh x, y, md z. Detziß a'bort the ranf) tunction are available in Chapter 3, "Standad I/O and PrcprocessorFunaions," as well as in Appendix A, "Library Functions Reference." I.9.2 ARRAYS An array is another slstem ofindirection. An anay is a data set ofa declared qpe, arranged in order An aray is declared like any other mriable or constant, except for the number of required array elernents: '' chai diq Ls'l0l; sLrl2ol; // // .his this decld es d. "!Ldy dectares an array oI of L0 : -ege s 20 characters The referencing of an anay element is handled by an index or subsaipt. The index can range from 0 to the length ofthe dedared array less 1. str l0l, strlll, strl2l, strtl9l Aray declarations can contain initializeß. In a variable anay, the initialization valueswill be placed in the program memory arca and copied into tlre ac.'lual.anay before nain) is q\ecut€d. A constmt atay ditrers in that the values will be allocated in program memory saving RAM memory which is usually in short supply on a microcontroller. A qpical initializer would appear as int arrayl5l = lI2, a5,21 56,94 \; In this czse,array[o] = 12, atmy[t] = 1s, amr[2] = 27, anay[sJ = 56,and arry[t] =ea. The C language has no provision for checking the boundaries ofan anay. Ifthe index were to be assigneda value that exceedsthe boundaries ofan arrayJmemory could be altered in an unetpected way, leading to unpredictable results. For example, c h a r d i s i t s [ 1 0 ] = { 0 ,7 , 2 , 3 , 4 , 5 , 6 , 1 , A , 9 I ; / / a n a r r a y o f c h a r a c t e r s 'u b - drs .sll2lt // rhis 'Fdds oursidc rhö d. o/ Arals are stored in sequential locations in memory Reading lig;/sJ in the axample above will causethe processorto go to the location ofthe fust index ofthe aray and then read the data 5 locations above that. Therefore, the second line ofcode abovewill causethe processor to read the data 12 spacesabovethe starting point for the array.Whatever data €xists at that location will be assrgred to numb ar.d lr:.aycausemany stmnge rcsults. So, as in many other programming areas,some caution and forethought should be ex€rcised. 45 46 A primary difference in tlrc useofan auay verms that ofa pointer is that in an array, an ac tual memory a-reahas been allocated for the data. With a pointer, only an addressreference location is allocated, and it is up to the programmer to declare and defrne the nctual mem orv areas(variables) to be accessed. The most common array type is the character anay. It is typically referred to as a string or character string. A string rqriable is dcfined asan array ofcharacters, while a constant süing is qpically declared by placing a line of t€x1 in quotes. ln the caseofa constant string, the C compiler will null-terminate, or add a zero to the end of the string. When you declare character strings, constant or variable, thc dedared array size should be one more than what is neededfor the contents, in order to allow for the null terminator: // variable strinq t-oq a_ _6-o -\ consE csr!{161 = ,,Constant strins ; // constant stsring in progran menory csrr in the example above is set to contain sirlccn values becausethe string itself contarns fifteen charactersand one more spacemust bc allowed for the terminator An aray name followed by an index may referencethe individual elemcnts of an aray ofarry qpe- It is also possible to reference the 6lst element of any aral' by its name alone. When no index is spccified, the array name is treated asthe addressofthe fust element in the lr-üay. Given the following declarations, c h a r s t n q [ 2 0] t the assignment p = srnq; // p is pointinq ro slnq[o] P = &stns[0]; // p is pointins to stnqlol Character strings often need to be handled on a character-by character basis. Sending a messageto a serial devicc or an LCD (Liquid Crystal Display) arc examplesofthis requirement. The examplebelow shows how array indexing and pointer indirection tunction ner rly interchangeablyThisexampleusesthe library tuncdorL2atthar) to se,one characterat a time to the standard output device, most likel)', a serial port: +include <stdio - h> const char s{151 = {"This is a tesL"); Enbedded C Langtdge Trtorial void nain (void) for{i=0; i<15; p!-.hq!rs p i++) i l); = s; for(i=0; i<15; i++) pulchar{*p++); // // print by each cha.acier of -sinq i ds än index, the array a qhole // point // // Print each character of lhe array anil nove to the nex! element p. by increnenLing the poinler Lo strinq as whj.l-e ( 1) ) The flrst portion on this program usesa for loop to output each character of the array individually The for loop counter is used as the index to retrieve each character of the anay so that it can be passedto the ? fchar) fücrion.'fhe second portion usesa pointer to access each element ofthe affay. The line ! = s" sets the pointer to the addressof the 6rct character in the aray. The for loop then usesthe pointer (post-incrementing it each time) to reo1evethe ,iaay elements ard pzssthem to putüar). ARRAYS I.9.3 MULTIDIT.,IENSIONAL The C language supports multidimensional arrals. When a multidimensional atay is declared, it should be thought of as arals of ara1s. Multidirnensional aral's can be constructed to have t!vo, thr€e, four, or more dimensions. The adacent memory locations are always referencedby the right most index ofthe declaradon. A qpical two dimensional aray ofintegers would be dedared as int two dlsl t10l; In memory, the elements of the array would be stored in sequential rows like this: ... cwod[0]t91, t w o d l 0 l l 0 l , t v o _ a l I 0 lt 1 l , t w o d i 0 l l 2 l . tro dt1ll0l, two_dl1lt1l, two alllll2l. ... rwo dl1ll9l, tvo,dl2li0l, two_dl2ll1l, tvo d12ll2l, ... rpo-dl2lt9l, Evo,dl3ll0l, two dl3lt1l, two all3ll2l, ... rwo-dl3ll9l, rwo dl4lt0l, two-dI4ll1l, two all4lt2l, ... Evo-dl4ll9l When a two-dimensional anay is initialized, the layout is the same,sequential rows: int natriai3l t4l = { 0. t, 2, 3, 4.5, 6, 1, a. 9, L0' r! li MuJtidimensional arraysare useirl in operations such as matix arithmetic, fr1ters,and lookup+ables (LUTs). For instance, assumewe have a telephone kelpad that genemtesa row and column indication, or scan code, whenever a key is pressed-A two-dirnensional aray could be used as a 47 ,l{l look-up-table to convert the scan code to the actual ASCII character for the key We will assumefor this example rhat the rnine getkefeode)scansthe keys and sets the rou and.eol values to indicate the position of the key that is pressed.The code to perform the conversion operation may look something like this: +inctude char <stdio.h> // *ro{, char *col); Lhe gFl kay.odF roucine // retDtns gretkeycode (char TRUE if for ascrr /* look up table consts char keysl4l t3l = { a key r\c qets is pressed, r_l prass FALSE if dnd not */ values !','2 , 3 , ,*,,,0,,,+,); void nain(void) { char row, col; while(1) // while forever' ' ' - t = qeEkeycode { &row, &col); there was a key plessed // aP.VE, if key lhat // and. row anal col conrain if (i == TRUE) the key value that ls // only print i PuEchar {keys Irowl tcoll pressed ) ; ) J Another, more common, form ofa two-dimensionat array is an array ofstrings. This example declaresan array ofstrings initialized to the dals ofthe week: char day of_the_weeklTl I10l = { Eflbedded C Language Ttlatial In the array shown above,the strings are of different lengths. The compiler places the null terminator after the last chancter in the string no matrer how long the string may be. Any wasted locations in memory are left uninitialized. Funaions such as2räff, print the string until they encounter the null-terminator character,thus being able to print strings ofvarr ous lengths correcdy To accessthe fourth day ofthe week and print the associatedstring, we wi[:lse printf). pr;nfl) teq'rnes the ad&ess of the fiJst chäracter of a string: o -r'Cs, ,/ 3d-J_o__.he.weeklJll0.): p!in n6one oqy The name ofa string is consideredto be the addressofthe fust character ofthat string. Stat ing only the lirst dimension is effectively referencing the entire string as the second dimension. So the same stdng within the array shown abovecan be accessedas printf("9s", day of the week[3] )i // prints itednesday I.9,4 POINTERSTO FUNCTIONS One ofthe more esoteric and powerfirl aspectsofpointen and indirection is that they can also be applied to functions. Using a pointer to a function allows for functions to be called fiom the result of look-up-table operation- Pointers to functions also allow functions to be passedby referenceto other functions. This can be used to create a dynamic flow of execution, which is sometimes called "self-modifying" code. Consider an example that calls a function ftom a table ofpointers to functions. In the fo1lowing example, tbe seanf| t:utrctton gets a value &om the standard input. The value is checked to make sure it is in range (1-6)- Ifit is an appropriate value,lnc nanber is used as an index into an array of function pointers. The anay v te at the func number index s assignedtoft, which is a pointer to a function ofgpe void. Remember from the "Functioni section (Section 1.8) that the standard form ofa function is type function_nane ( I stalementl; sLalenent2; ] which is a qpe, followed by a name, followed by the primary operator //. The parentheses, or tunction operator, indicate to the compiler that the identifer is to be treated as a function. In this case,f contains the addressofa tunction. The indirection operator is added to obtain the addressofthe function from the pointer,p- Now the tunction can be called by simply adding the tunction operator //,like this: llfpl ( j Here is the entire progam: + i n cl u d e < s t d i o . h > t\c fun.t io- poinred .o b\ p 49 50 void do s tari rasli(voiC) { prinrf ( s_!a.t selected\n ); ) voad do qrinEi void Lasli (\roiC) srop 1 stop (vo id) io_up-:ask printf selected\a,! ) ; ( !p selec:ec\. ); ) void do down tas{ (void) I void do Lefr task(vord) { printf ('1e:. selec:ed\n ), ] void do riqh: task(vord) ] vold {*Lask do starL do oo do dosn do lefL do right listt5l) ias,{, (vord) = { or ".I. po 6. o task, task, tas:{, ); voii nain (vord ) { in. func .lmber; void l-fp) {void) , r- fp is a Fornter to a funcLion */ Enbedded C La"gtage scanf ("*d",&func if((func { nünler), nunber > 0) && {func nunber < 7)) I isL I fun-_a ]mbe'- ldslfp (*fp) O; /* ] Tutaria/ and call Lhe selecred : */ function ) Chapter I Example Proiect: Part C In this phaseofthe development ofthe Pocket Slot Machine, we are going t 'polish ations and multidimensional arrays to the pmjectt appearance.Instead of printing numbers for the column values and referencing numbers in our payout calculations, we will give these values nanes. // SloE +incLude Machine" The üini <MEGA8515.h> Exercase /t processor /* quartz specific *define xraL +define baud 9600 /+ crystal l/ Baud rate <stdio.h> /' rl-:s #include // clobal +define 4000000L Declarations. Variable first, second, third; // JACKPOT enum { BAR, BEL!. char kindl4l I8l 3 2 1 0 frequency r\e pr inr t{r lHzl */ */ derinrfron ' . colums in the nunbe. to forn a s e e d f o r general purpose a variable for randon +s payouts */ /a This alefines siwe different /* ntues ln order to n a k e L h e c o d e n o r e * / /* reaalable to hunans LEMON, CHERRY }; = { qar s infornation // // fo! the kinds values of for names each kiad 5l 52 "LEMON" , vold flash liqhts(char n) flash // the liqhts a nunbe! of tines I for(counr = 0; count < n, count++) flash // lisht vhen done. { for{de1ay = 0; = 0; lORfB.l for lde1ay = 0; PORTB.I - delay < 10000, // just ale1ay++) turo < 10000; the LED on.. delay++) // delay 1; turn // count the up anal wait LED off., ) ) { == CHERRY) && (second == CHERRY) && (thitd == CHERRY) return JACKPOT; "cherries".. // if att == CHERRY) | | tsecona == cttERRY) | l else if ( (first (third = = C H E R R Y )) if{(first else refurn DIJ'48; // i dnj ä e "cherries ,. == second) && (second == Ehird)) if((first . ,ht-e dre rcrurn Nlc,{EL; // ile, ot "ny "l return void zERo, // // lose. nain(void) PORTA = OXFF, DDRA = 0x00; DDRB = 0x00; DDRB = 0x02; / / you otherwise // // declare // tempora.y a local // pörL a -rr // porL B-1 wariable for use.. i.prt" is an outpuE Taltialize the UART concrol redister Rx & Tx enabled, e data biLs UCSRB=0x18; i-i"Iize Lhe UAR'I's bducl räLe (1iqhE) k:nd,, C Lang"age Txtorial Enbedd.d rhi le (1) {hiLe d.ö fotelet / / (PINA.0) second // waiL // LeL // over fot a bü!!on tlle counter Lö forn = seed; = third and !o11 ower and a seed, preload // the colums up the nunbers qaiEinqr for button // Mix // while ^= seed>>1; // Exclusiwe second^= seed>>2; Ehird ^= seed>>3; // caD rea1ly // // Keep lol1inq ower the seed paEEeln qhile Ehe bDtton is pressed. // flash I filst ) while(pINA-o == O); fLash_lights(5); first &= 3; printf('--> nunber in the novind stir up the nunbels. tishts lhe to walues fron // B Y N A M E! ! show Ehe va1ues.. si.@Iy chanqe the gd to Ss ro the string aDd pass the pointer kindll lo Plinlfo t1re 2D array as < \n', Ss, kindtti!sLL // // 0 Eo 3 1lnit // // gs, r i.d lsccond l, deEernine kinolrnitdl a r)ayout. aow print the payout , resulEs I ZERO: prlnrf( "Paiat ouE: zERo\n') t break; NICKEL: prinEf("Faid out: one Nicket\n plintf("Paial out: one Dlne\n ); ); seed 5 lines,. = set_payouh{); svitch(i) release, ORioq // // i . . ); from 54 JACKPOT: p!intf('Paid out: I.I O STRUCTURES AND J a C K P O T !! \ n ,; UNIONS Structures and rmions are used to group variablesunder one heading or name. Since the word 'bbject" in C programming generally reGn to a group or associationofdata members,stmc tures and unions are tlle fundamental elements in onject-orientedprogranning. Object oriented programming (OOP) refen to the method in which a program dealswith data on a relational basis.A stluctule or union canbe thought ofas an object.The membersofthe structure or union are the properties (vaiablcs) of that object. The object name, then, provides a meansto identifi the associationofthe properti€s to the object rhroughout the program. I.IO.I STRUCTURES A structure is a method ofcreating a single data object from one or more variables.The variableswithin a süucture are called members-This method allows for a collection ofmembers to be referencedftom a single name. Sone high-level languagesrefer to this q?e of object as a record or based-rariablc. Unlike an arrav, the variables contained within a srructure do not needto be ofthe samcgpe. A structure declaration has the following form: Lype Lype neniber_1; nenbe._2; type menber 1; tsype menber 2t type mefrber x, s t luchure var nane, J Once a sm:cture template has been defrr'ed, t}re structure_tag_rrn e serves as a common descriptor and car be used to declare structues of that tlpe throughout the program. Declared below are two structures, oarl and var2, and an array ofstructures zar3: stLuc' srtu^l !,c_ldq_."m- vdrl, röt2, vd,Jt5lj Structure templates cän contain all sorts ofvariable gpes, including other structures, pointers to functions, and pointers to stucturcs- It shorid be noted that when a template is defined, no memory space is allocated. Memory is alJocatedwhen the actual sotcture variable is declared. Members within a structure are accessedusing the member operator (.)- The member oper ator connects the member name to the structure that it is associatedwith: structure va._nane.nember 1 struciure var nane.member x C Language Tulolia/ Eibedd.d Like arays, structures can be initializcd by following the structure name with a list ofinitializers in braces: DATE { inl ron slruct int int h, day; year; // declcle // dare d or lempldre ä sElucture a scructure variable aad inilialize // declare .l = | 2, 2t, 1961 srrucr DATE dare of birEh i it.. This yields the same result as these assignments: = 21; bilth.day -year = 1961, of-birth date of date Since structures themselves are a ralid gpe, there is no limit to the nesting of members within a structure. For example, rfa set ofstructur€s is dedared as STTUCL LOCAT]ON int int I x; y; // Ehis is Ehe tocatiod coordinates x and y )t siluci PART { cha! par!-nanel2ol t lonq int sku; LocATIoN bln; slruct // a string // // a sKU nunbe! iLs localion che parts nane for the part in the warehouse for ] widqet; To accessthe location ofa "widget," you would provide a rderence Iike this: // the x cooldinate of the bin of the widqeE // the y coordiDate of the bin of the widget To assign the location of the "widget," the samerules apply: widget,bin.r = 10; // the x cooralinate of rhe bin of the widget widqet,bi!.y = 23; // the y cooralinate of rhe bi! of the widget A structure can be passedto a function as a parameter as well as returned from a function. For example,the flrnction slluct PART nes location{ sLruct inl x, int y) PART temp; temp,parts .oane = Oi temp,sku cemp,bin.x - x; renp. orn. y = y; = ""; // j,niLialized // zero // sqt the nane !o NULL the sku nunbe! ttq lordtion to fhe pdssed x d d 55 56 // dd Ehen returns the structure to the ca11er ) would retum a PART structure with the ,ä,r and är-J' location members assignedto the parameters passedto the function. The slz and part nane rnemberc would also be cleared before the structure was returned. The function above could then bc used in an assigr ment like widqer = new location (10,101 ; The result would be that t\e part naru ?nd,:Auwanld be deared and the ollger./iz.x widgx.bin.y tnlttes wodd b€ set to 10. and I,IO.2 ARRAYSOF STRUCTURES As with any other variable type, arrays ofstructur€s can also be declared.The declaration of an array ofstructures appearsas follows: struct PART { char part_nane struct I2 0l ,. // // LOCATION bin; a sKU nunber for the part irs location in the warehouse ] wtdgeL[100]; The accessofa member is still the same.The only difference is in the indexing ofthe struc ture vuiable itsell So, to accessa "particular widget's location," a referencelike this may be used: x_1ocalion y_1ocalion = widqet [12] .bin-x; // fha x ôordindte = widgret [12] .bin-y; // rhe y ôordinäle or !he bin o! or rhe bin ol -h- 72 widg-- he wiclq-- 12 In this example,there is a ch;rlctet strirrg ?art nazs, which can be accessedas strings normally are: widgetll2l.part_nae; wid9ret [12] .part nane t0l ; // Lhe fi-tst // the nane character of in widset 12 the nane of widqe! 12 Arrays ofstructures can be initialized by following the structure name with a list of initial izers in braces; there simply needs to be an initializer for each structure element within each int ) nontsh; Enbedded C LangLdge Tttari4l stluc! DA'r'Ebirthdaces[3] - { 2, 21, 1961-, a, a, L974, '1 71, 1997 , l; I.IO.3 POINTERSTOSTRUCTURES Sometimes it is desirableto manipulate the membeß ofa structure h a generalized fashion. One method ofdoing this is to use a pointer to referenceth€ structure, for example,passlng a pointer to a structure to a function instead ofpassing the entire structure. A pointer to a sducture is dedared as follolrr: The pointer operator (*) states that st'uetare_t'ar-nane is z poittet to a structure of gpe structure tag name. J:ustas with any other qpe, a pointer must be assigned a value that points to something tangible, like a rriable that has already been dedared. A variable declaration guaranteesmemory has been allocated for a puryose The following code would be used to declare the structule rariable, ru:7gel,and a pointer to a structure variable, lilzrlgee The fnal line in the example assignsthe addrcssol uidget to the polnter th;s_lridgetstruci LOCAT1ON { in! x; int y; // chis is che location coordinates for x and y ); struct PART { char part_nanel2ol1 -r s\u; rons // a sLring // d SKU numbFr ror struct // its LOCATION bin; location rhe in paic nane -h6 parthe warehouse ), struct rthis widger; PART widqet, d e c l a r e // a structsure and a poinLer // to a sLructure assigr! the pointer the adalress of a slructure \4lhen a pointer is used to reference a structure, the strucnrre pointer operator, -> (minusgreater-than), is used to access the members ofthe structure through indirection: lhis vidqer >sku = 1234; This could also be stated using the indireaion operator to fi$t locate the structur€ xnd then using the member operator to access the slz member: (*this-widset) -sku = 1234; 57 58 Snce tbi uidget is a pointcr to zolgat, both methods of assignment, shown above, are valid. The parenthesesarovÄ lbi-zoilget Ne rcguired becausethe member operator has a higher precedencethan the indnection (*) operator- If the parcntheseswere omitted, the erpressionwould be misinterpretedas which is the actual addressof.pllgar (&widge$. Structures can contain pointers to other structures but can also contain pointers to structues ofthe sameqpc. A structüe cannot cortain itselfas a mcmber, becausethnt would be a recursive declaration, and the conpiler would lack the information required to resolve the declaration. Pointers are ahvals the samesize regardlcssofwhat they point to. Therefore, by pointing to a stucture of the sametype, a structurccan be made'telf-referential.'A very basic example would be as follows: strucl I LIST_I:CEI4 { char *string; int position; 'r I'STr-EM'n-yr irem, !ten. // // a LexL string its positio. in a List ,tFn;1/d po-6 ooo a iLem2; next = &iten2; iten äss 9n lh- poin.P. wit -h. .oo'--- Now is thepasr'riazmember ofthe structure pointed to by next ien.This.no.id be equimlent to aEem2,position Self referential structures ,re qpicallv used for data manipulations like linkedlists quick sorts. and 1.10.4uNroNs A union is dedared and accessedmuch likc a structure. A union declaration has the following form: unaon ); unioa raq nane type lype senbe! nenbe! 1; 2; type nember x; union { union taq Lype type ot ) union name { nember nember tsype nenbe! war_nane; 1; 2; x; The primary difference betrvcen a union and a stncture is in the ray the mcmory is allo *rted. The members of a union actually share a common memory allocated to the largesr Enbedded C Lahg"dge Tutar;dt memberofthat union: union SOME TYPES { char character; rnt integer; long ] ny int long one, space, In this example, the total amount ofrnemory alloc ted to mJ s?aceisequir"lent to th€ size ol the long ir't long-one (a bftes). Ifa value is assignedto the long int, my_space . lons_one = Ox1-234561ALt thent\e vall:eof my space.c])aructet andnf s?aee.integr nrealsomodtÄed.Inthis case,their ralueswould now bc my space.character = 0x12; m y s p a c e .i n t e g e r = 0 x 1 2 3 4 ; Unions are sometimes used as a method ofpreservhg valuable memory space.Ifthere are rariables that are used on a ternporary basis, arrd there is never a chance thxt they will be used at the same time, a union is a nethod for defining a "scratch pad" areaofmemory More often, a union is uscd asa method ofsrtracting smaller parts ofdata from a larger data object. This is shown in the previous example. The position ofthe actual data depends on the data q?es used nnd how a particular compiler handles numbers larger than 9?e char (8 bits). The example above assurna bigendian (most significant byte tust) storage. Compilers vary in how they store data. The data could be byte order swapped,word order swapped, or bothl This example could be used as a test for a compiler in order to 6nd out how the data is orgnized in memory Union declarations can savesteps in coding to coß€n the format ofdata from one organization to another. Shown below are two enarnpleswhere two 8 bit input ports are combined in one 16-bit ralue. The lirst method usesshifting and combining; the second method uses +incLude +incLude void <stdio. h> <MEGA8535.h> // register definition // an atnel aTMEGA8535 header file for nain (void) unsigned int port v, vhi re (1) q: polt P]NA; po!ts q <<= 8; oo ! q I P-NB; // // // get port A into the iL up.. now .onbinF r po. 16 bit shift B vaLue 59 60 p!inlf = A04x\n",poll v) ; / / puE the conbined ( "16 BlEs I the // . slanddld walue ouE to o-lpur Now the same results using a uaion declaration: +incLude <stdio.h> +include <MEGA8535,h> // register alefinition // an atnet aTMEGA8535 // // declare a union header file for nain (woid) void t lhe lwo types of data in Lo occupy the sane space., unsigned char port b[2]; unsigned int port s,. v a l u e ; ] whi le (1) = pINA; = pINB; walue.portblo] waLue.portbl1] // // prinEf( 16 BiEs ) // qret port A // qret port B Ehe union elininares need to conbine the Ehe data // nanually = 304x\n",va1ue.por!_w) ; / / put rhe conbineal walue // L'e s.dnd. d o..p. out to I.IO.5 TYPEDEFOPERATOR The C languagesupporsan operationthat allowsfor creatingnewgpe names.The gpedef operatorallowsfor a narneto be declaredsynon).rnous with an existingtype.For example, LlpeoeJ typedef .nsigneo unsigned char byr e, iDL rord; Now the aliases"bne" and "word" can be used to dedare other variables that are actually of qpe unsigned char and unsigned int. byce varl: wotd vdt2; '/ // this Lhis is is Ehe same ds an unsiqnecl clc Lhe sqme ds dn unsiqned ir L This method ofalias works for structures and unions asu.ell: typedef struct I char nane t 20l ; coar age; int hone roon nuhle.; ] student; Enbedded C Langl'ge stsudent Bob; sEudent sa11y; Tltori.l // these allocaEe menory in bhe forn of // a structure of lype srudenL The #define statement is sometimes used to perfonn this alias operation through a text substitution in the comp;Ier's preprocessor.gpedd is evaluated by the compiler directly and can work with dedarations, castings, and usagesdrat would exceed the capabilities of I . I 0 . 6 B I T SA N D B I T F I E L D S Bits and bitfelds are often used when memory space is at a premium- Some compüers support a gpe bit, which is automatically allocated by the mmpiler and is refereoced as a l.ariable ofits own. For example, blr running; // = 1; = 0; runninq runninq if the conpiter // storage // Llle only // El)e vatue for tso allocaEes a sinqte bit of f1aq.. this possibilities for value are 1 and 0 (running) ; can be testeal as vel1 as assigned Unlike bits, bitfrelds are more mrrmon for larger, more generalized s1.'stemsand are not alrvals supported by embedded compilen. Bitfields are associated with structures because of the form ofthen declamtion: unsisned ,". n.-O int biE-1:1; .' O',-'r'r, unsisneil j j ' int ,..'s.-d i.' struct_var_nane; bit-l :1; U.-'t, , A bitfield is specified by a memb€r name (oftype unsigned int only), followed by a colon 11 and th€ number ofbits required for the value- The width of the member can be ftom 1 to the siz€ of tne unsigned ht (16 bits). This ,llows several bitfields within a structure to be rcprcsentedin a singleunsignedintegermemorylocation. struct { unsisned unsisned unsisned I nachine, These bitfelds iaE inE inE runninq sropped counter : 1; : 1; : 4; can be accessed by member Irame, just as you would for a structure: nachine,stopped = 1, nachine. running = 0; // these are sinqle bits, 1 and 0 are a1loweal., so only 6l 62 nachine.counler++; // wa1ue, Ehis is 4 bit 0 15 are a11owed.. so Sometimesin embeddedqstems bitfields arc usedto describeI/O port pins: Lypedef stxuct bit 0: 1; bit 4: 1; biE,6:1; The following #define labels the contents of memory at location üI38. (Remember, #define is treated as a textual substitution directive by the preprocessor) This allows the programmer to accessmemorylocation0x38by the name PORTB,asif it werea variable,throughout the program: // PoRTB is the contents +define PoRT'B (* (birs *) of aalalress 0x38, a bitfield 0x38) "bits' The /it birfield allowsthe individualbits ofVO port PORIB to be accessed independendy (sometimes called"bit banged"): // bitfields P O R T B b. i t _ 3 PORTBb . i!_5 can = 1; = 0; be used in assiqrnneDts can also be useal in // biEfields if (PoRTB.bir_2 | | PoRTB.bir_1) = 1; P O R T B .b i t _ 4 conditional expressions I , I O . 7 S I Z E O FO P E R A T O R The C language supports a unary operator called sizeof This operator is a compile-time feature that createsa constant value related to the size ofa data object or its qpe. The forms ofthe sizeofoperation are as follows: s zeor( object r // cha!, 1ong, // object // structure, erc, could or be d vari-bIe. union variable " dy. nane Theseoperationsproducean integerthat revealsthe size(in bltes) ofthe gpe or dataobject locatedin the parenfieses.For exarnple,assumingthesedeclaratrons, int vatue,x; tonq int array 12I I3l ; Enbedded C Lang'age TLt.ria/ { char nanet24l; ] srudenrs[100]; here are some of the resulting possibilities: sizeof (value) ; x x = sizeof = sizeof // Lhis (array) ; // . = sizeof (record) \ would llonJ) set x=2, since an int set x=2, since value *array kidth*array lensth= 4*2'1 = 2- ; - 2at2 to. r'e.hd!d^r Fr stJing x = sizeof(sLudents), // x = 100 Elmentss t (24 characrers // x = 140'(24+21 =26AA ll I.I I is 2 bytes is an inE p - + sizeof(inL) ) MEMORY TYPES The architecture ofa microprocessormay require that variablesand constantsbe storcd in dif ferent qpes of memory. Data that will not change should be stored in one type of memory while data that must be read fiom and wrinen to repetitivdy in a program should be stored in another 9?e of memory. A thnd gpe ofmemory can be usedto store variable data that must be retained evenwhen power is removed from the system-When special memory q?es such aspointers and register \'äiables are accessed,additional factors must be considered. I.II.I C O N S T A N T SA N D V A R I A B L E S The AVR microcontroller was designed using Hanard aichitecture, with separate address spaces for data (SRAM), progräm (FLASH), ard EEPROM memorp The CodeVisionAVR@ and other conpilers irnplement three gpes of memory descriptors to allow easyaccessto thesevery different rypes ofmemory. The default or automatic allocation ofvariables, where no memory descriptor ke)'word is used, is in SRAM. Constants can be placed in FI,ASH memory (program space)with the flash or const kel.words.For rariables to be placed in EEPROM, the eeprom ke) \,vordis used. When declarations are made, the positions ofthe 0ash and eegorn keywords become part ofthe meaning. Ifcons! flash, or €eprom appear first, this states to the compiler that the actual allocation of storage or the location of data is in that memory area. If the gpe n dcclared lollowed by the flash or eeprom kelvord, this indicates that it is a r.ariable that rrf rrezas FLASH or EEPROM, but the variable itself is phlsically located in SRAM. This scenariois used rvhen dedaJing pointers into FLASH or EEPROM. 63 The following declaratiom will place physical data direcdy in program memory (FLASH). These data values are all constant and cannot be changed in arryway by pro$am execution: '_"sh i! __"si _o :nteqer_const"nt 9 ro,q_int_co-s.antl lonq lonq_ints_constants2 ' !ese -. drraylll fLash | 2Jn ); 99L; = 0x10000000; |L2.1); two elenents will be 1 and 2, // The first = fLash int lnteger_aftay2 [10] {1,2\; the rest vill be 0 = I11,2,31 , 14,a,6l I t const char stiing -'TF constant2 [] -g s is älso ä sr- int a; cha! bt3l, ct3l; ] s f = { { 0 x 0 0 0 a 1 , { 0 x b l , 0 x b 2 , 0 x 1 t r 3 }{,0 x b 1 , 0 x b 2 , 0 x b 3} I ; EEPROM space is a non-volatile yet variable area ofmemory- Vaiables can be placed in EEPROM memorysimplyby declaration: dllocdtes inteser "n a 20 byte allocates eepron s.rucr char | sp"ce area in -tDDOv EEPROI4 r ct15l; // allocates 19-b1'te structure "se" in EEPRoM Thesepermanent(FLASH) and semi-permanent(EEPROM) memory areashavemany system-specilicusesin the embeddedworld. FIÄSH spaceis an excellentar€afor nonchangingdata.The programcodeitself residesin this region.Declaringitems suchastext stringsard arithmeticlook-up-tablesin this regiondirecdyfreesup valuableSRAM space. If a string is declaredwith an initializer like ch" vs! r '.o lJ0l "'rhis sLrinq is placed jn SRAI4: 30 bltes of SRAM wil be allocated,and the text "This string is placedin SRAM" is physically placedin FLASH memorywith the program.On startup,this FLASH residentdata is copiedto SRAM and the programworksftom SRAM wheneveraccessing qrtring.'fhts is a wasteof30 bytesof SRÄM unlessthe string is intendedfor alterationby the program during run time. To preventthis lossof SRAM space,the string couldbe storedin FI,ASH memorydirecdyby the dedaration: ' "sh .hä. mjsl : g[10 'This sl r'aq is p d ad in SRAT , Eabedded C Lungtage Tttariat The EEPROM areais called non volatile, meaning that when power is removed from the microprocessorthe data will rcmain intact, but it is semipermanent in that the program can alter the data located in this region. EEPROM also has a life-it has a maximum number ofwrite cycles that can be performed before it will electrically fail. This is due to the way thät EEPROM nemory itself is constructed, a function of electro-chemistry In many cäses,this memory area will have a rating of 10,000 write operations, ma.rdmum.Newer technologies are being developed all the time, increasing the number ofwrite operation to the hundreds of thousänds, even millions- There are no limitations on the number of times the data can be read. It is important to understand this phpical constraint when designing software that uses EEPROM. Data that needsto be kept and does not change ftequently can be stored in ttls area.This region is g:eat for low-speed data logging, calibration tables, runtime hour meters, and software setup and conf,guration valuest.I t.2 PotNTERS Pointers to these special memory regions are each hardled differendy duriog program execution. Even though the pointers can point to FI-ASH and EEPROM memory areas,the pointers themselves are alwals stored in SRÄM.In these cases,the allocations are normal (char, int, and so on) but the g?e of memory being referenced must be described so that the compiler can generate the proper code for accessingthe desned legion. The flash and eeprom keyrvords in these casesare used to expound on the name,like this: cha! cha! 'h-! *pt! flash ro /* Pointer ran = "This *pt! /* Pointer to tlash tö a strins that is located sering is placed in sRÄM", ho a string that = "This strins is Lo a string that /* Poinrer eeprom rpF! fo eaprom - " rhis sr ' in9 is locaLed placed in is locaLed is pld.-d in SRAM */ in FLASH */ FLASH'; in EEPRoM */ --Poov ' I.I I.3 REGISTERVARIABLES The SRAM areaof the AVR microcontroller indudes a region ca11edthe Register Fi1e.Tnrs region contains VO ports, timers, and other peripherals, as well as some "working" or 'tcratch pad" area.To instuuct the compiler to allocate a variable to a register or (egisters,the storagedass modifier register must be used. reqister inl abc; The compiler may choose to automatically allocate a rariable to a register or registers, even ifthis modifier is not used.In order to prc\,ent a vadable fiom being allocated to a register or registers, the volatile modifier must be used. This wams the compiler that the variable may be subject to outside change during cvaluation. volatile int abc; 55 The volatile modilier is fiequendy used in applicadons \dhere vrriables are stored in SRAM while the microcontroller sleeps- (Sleep is a stopped, low-power mode gpically used in battery applications.) This allows the value in SRAM to be valid each time the microcontroller is awakened and returned to normal operation. Global variables that have not been allocated to reeistersare stored in the General or Global Variable area of SRÄM. Locrl variables that have not been atlocated to registers are stored in dynamicalty allocated spacein the Data Stack or Heap Spacearea of SRAM. sfrb and sfrw The I/O ports and peripherals are located in the register file. Therefore, specialinstructions are used to indicate to the compiler the ditrerence between an SRAM location, an VO port, or another peripherälin the register file. The sftb and sfrw kelwords indicate to the compiler that the IN and OUT assemblyinstructions are to be used to accessthe AVR microcontroller's I/O reeisters: ion sfrb PINA=0X19; sf!b sf!b sfrw TCNTI],=0x2c; TCNTlH=0x2d; TcN'l l=0x2c,. void main (void) // R F gi s I F r s rsFR)' // I bir access to lower parE of riner // 8 t'it access ro uppe! parE of riner tb bit dc.ess to the rime- runs:gned -.. t TCNT1=0x1111; // // Read wriEe PORTA inputs pins to TCNTIL & TCNTIH registers ) The bit-level accessto the VO registers is allowed by using bit selectorsappeflded after the nnme ofthe yO r%ister. Becausebitlevel accessto VO registers is done using the CBI, SBI, SBIC, and SBIS assemblylanguage instructions, the register addressmust be in the 0x00 to 0x1F range for declarations using s&b, and in the O,<00to 0x1E range for declantions using sfrw. For example, sfib sfrb sfrb PoRTA=0a1b; DDRA=0X18; PINA=0X19,. void nai! (void) Embedded C Language Tutotial 0 of Porl A as outpu! D D R A .1 0ofPor!Atsoa1 t if (PrNA.1) PORTA.O = *"*y in" kelw,ords are found in a header files included at the top ofthe "*, ""0 "* progran with the #include preprocessordirective. These header files are gpically related to a particular processor.The header files pmvide predetermined namesfor the VO and other usefirl registers in the microcontroller being used in a particular application. Listed below is a t)"ical (MEGA8515.h): // I/o indude file that might be provided with registers definiEions sfrb OSCCAL=4; sfrb PINE=s; sfrb DDRE=6; sfrb PORTE=?; sfrb ACSR=8; sftb UBRRL=9, sfrb UCSRB=oXa; sfrb, UCSRÄ=oxb, sfrb' UDR=oxc, sfrb sPcR=oxd, sfrb sPsR=oxe; sfrb SPDR=oxf; sfrb PIND=0x10, sfrb DDRD=0x11, sfrb PoRTD=ox12, sfrb PINC=0x13; sfrb DDRC=0x14, sfrb PoRTc=oxl5; sf!b PINB=0x16, sfrb DDRB=0x1?; sfrb PORTB=0x18, sfrb PINA=0x19; sfrb DDR-\=0x1a; sfrt' PoRTA=ox1b; sfrt' EECR=0x1c; sfrb EEDR=0x1d; for the ATI{8G48515 a compiler 67 6a sfrb sfrw sfrb sfrb sfrb sfrb sfrb sfrw sfrb sfrb sfrw sfrl' sfrt' sffu sfrb sfrt' sf.w slrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb sfrb EEARH=0a1f; EEAR=0x1e,. // UBRRII=0a20; UCSRC=0a20; WDTCR=0x21; ICR1L=0x24; ICR1H=0x25; ICR1=0x24; // oCRIBL=0x28; OCRIBH=0x29,. ocRlB=ox2a; // OCRIAIJ=0x2a; ocRlAII=0x2b; ocRlÄ=0x2a; // TCNTIL=0x2c; TcliITlH=0x2al, TcNTI:ox2c; // TCCRIB=0x2e; TCCRIA=0x2f, SFIoR=0x30; OCRo=0x31; TCNTo=0x32; TCCRo=0x33; üCüCSR=0x34; MCIJCR=0x35; EMCUCR=0x36; SPMCR=0x37; TIFR=0x3a; TMSK=0x39; GIFR=0x3a; GICR=0x3b; sf.b SREG=0x3f; // Interrup! vectors EXT_INTO 2 EXT_INTI 3 TIMI_CAPT 4 TIMI_COI{PA 5 TIMI_COI{PB 6 TIMI_OVF 7 16 bil access 16-t it access 16-t'it access 16-bit access 16 bia access alefiniEions Enb?dded C Lan{uage Trto,it/ TIMO OVF 8 SPI_STC 9 USART RXC 10 USART UDRE 11 USART TXC 12 ÄNA.COMP 1f EXT fNT2 14 TIMO.COMP 15 EE RDY 16 I.I2 REAL-TIME METHODS Real-time programming is somctimes misconstrued as some sort of compler and maeical pro"essrhrt can onll be performedon largc mac}rheswirh operaringsy"rernrlike LinJx or Unix. \or .oi Embedded.ysremscar, in many cxes, perfoim on a more real rime brsq than a largesystem. A simple program may run its courseover and over It may be able to respond to changcsto the hardware environmenr it operatesin, but it will do so in its own rime. The termireltime" is used to indicate that a program frrnction is capableofperforming all ofits flnctions in a regimented way within a certain allotment oftime. The term mav also indicate thar a orog'am ha" rhe abil;g ro respondimmediarelyro oudde (hardwaJeinpur) jr:Tulur. The A\rR, with its ich periph€ml se! has the äbility to not only respond to hardware timers, but to input changesaswell- The ability ofa progmm ro rcspond to these real-world c\a.lgcsi. caled ;nrerrupror exceptionprocessing. I . I 2 . I U S I N GI N T E R R U P T S An interupt isjust that, an exception, change offlow, or intemrption in the program operat;on cnused by an arternal or internal hardware source. An internpt ii, i; effect, , hardware-generated function call- The result is that rhe interrupr wiJl cause rhe flow of e{ecution to pausewhile tie intemrpt function, called the interupt serviceroutine (ISR), rs erecuted.Upon completion of the ISR, the program flow wilt resurne,c.rnrinuing from where it was interupted. In an AVR, an interrupt will causethe sratus rcgister and program counter to be placed on the stack, and, bascd on the source ofthe interupt, the proglam counter will bc assigaeda value lrom a tablc ofaddresses.These addresses,re refered to as vector Once a program has been redirected by intemrpt vcctoring, it can be returned to normal op eration through the machine instmction RETI (RETirm from Interruot). The RETI nr stnrction restotes the status rcgister to irs pre-intcrnrpt value and the program counrer "ets to the next machine instruction following the one thar was interupted. 69 70 There aremany sourcesofintermpts availableon the AVR microcontroller.The largerthe AVR, the more sourcesthat arc available.Listed belowaresomeofthe possibilities.These def,nitionsare usuallyfound in a header6le, at the top of program,and are specificto a given microprocessor. Thesewould be found in a headerfor an ATMegal28, Mega128.h: - !e rupt vectors detinitions +define +define +define +define +define #define +define +define +define +define +define +defi.e +define +define +define +define +deflne +define +define +define +define +define +define +define +define +define sdefine *define +define #define #define +define +define +define Exr rNTo 2 EXT_INT1 l EXT_INT2 4 ExT_rNTl 5 EXT_INT4 6 ExT rNT5 ? ExT rNT6 8 ExT fNT? 9 Trlr2 coMP 10 Trn2 ovF 11 TrMl CAPT 12 TrMl coMPA 13 TrMl coMPB 14 TrMl ovF 15 TrMo coMP 16 TrMo ovF 17 SPr STC 1a U S A R T oR x C 1 9 U S A R a c o _ D R2E0 U S A R T o _ T X C2 1 ADC_INT 22 E E _ R D Y2 l ANA_COüP 24 TIMI_COüPC 25 TIM3_CAPT26 T I M 3 _ C O ü P A2 7 Trnt3_col{PB 28 TrM3 col{Pc 29 TrM3_ovF 30 U S A R T I _ R X C3 1 U S A R T I _ D R E1 2 usaRTl_Txc 33 Tirr 34 sPM RDY 35 This list contains a series ofvector indices associated with a name describing the inte(upt source. To aeate an ISR, the function that is catled by the intemrpt system, the ISR, is de- claredusingthe resewedword intemrpt asa frrnctiong?e modi6€r. interrup! [EXT_INTo] void exlernal inro(void) Enbedded C L'rguge T"toria/ t /* catled äutonatically on external 0 */ interrupt I inEelfupt /* ITIMo catled ovFl woid Linero autonaEically owerflow(void) on TIMERo overflow */ The inteffupt kelr,.ord is followed by an index, which is the r,cctor location of the interrupt sorrce. The \'€ctor numbers start with [1], but since the first vector is the reset vector, the actual interupt vectors ävailable to the programrner begin with [2]. ISRs can be executedat any tirne, once the intemrpt sourcesarc initialized and the global interrupts are enabled. The lSR cännot return any values, since technically there is no "cal1er,'ard it is alwal.s dedared as gpe void. It is for this samereason that nothing can be passedto the ISR. Inteffupts in an embeddedenvironment can genuinely createa real-time execution. It is not uncommon in a peripheral-rich system to see arr empty zubile(1) loop Ln $e nain0 ftrction. In these cases,zaä1J simply initializes the hard\,%reand the interrupts perfom all the necessarytaskswhen they need to hnppen// I/O legiste. definitions <M8cA8515. h> +include for // quartz crystal frequency +define xTÄL 4000000 [Hz] // LED blink +define Blink // // TIMERI occurs inteüupt frequency Rate ATI{EGA8515 [Hz] 2 ovelf1ow interrupt every 0.5 seconds ITIM1-OVFl void service tinerl overflow(void) // presets again TIMER1 ( XTAL /1024/ TcNTI=0x10000 PORTB-o ^= !; // routine toggle Btink the Rare); LSB of pORttB J woid nain (voial) { // ser the I/O ports and initiä1ize TTMER1 7l 72 DDRB=0x01,. // PORTB.o pin TCCRlA=0; TCCRlB=5; // TIr'IER1 is // TTMBR1 c10ck TCNT1=0x10000 IX.IAL/1024/ // clear dny TIMSK=oX80; // enable GIMSK=o; // all is disconnecled is from Rare); // I.tMhRl inte!!upc qlobal the "tinerl OCl, no Phrr"i enäble plese! TIMER1 flass interrupt overflos inlerrupt // pin xrat/1024 Btink TIl4ERl olher an oucput sources are disabled interrupts (1) done by overflow" function In thls exanple,nain) is usedto initialize the systemandenabletheTIMER1 overflowinteffupt. The interrupt futcüon tinerl ooerfow blinks the LED everyhalf second.Note th^t main) sitsi^ a ,."lilep,,lloop while the blinking goesonI.I2.2 REAL-TI]'IE EXECUTIVES A Real-Time Executive(RTX) or Real-Time Operating System(RTOS) is a proeram, commonlyreteffedto asa "kernel,"that coordinatesthe management?nd ex€cutionofmultipl€ sub-progrämsor "tasls." Arr RTX srrictly coordinatesprogramruntime operations, while an RTOS is usuallyassociated with e:<trxfunctionality suchasfile managementand other generalizedI/O operations.There are many rcal-time executivesavarlablefor the AVR. Somearein the public domain and are frce of charge.Others are commerciallylicensedand supportedbut arestill inexpensive. In this section,we areonly going to touch on the R.T)i, specifcallythe PrograsiveResourca'PR-RTX that is readilyavailableand sim ple to contrgureand use. An RTX utilizes a time-basedintenupt (i.e., TMER0) to guaianteethat various subprogramexecutionshappenon time and asoften asis requiredto obtain the desiredoperational results.The beauty of an RTX is that the program operation, from a timing perspective,is definedin a headerblock and the tasksarcusuallyconfiguredwith a call into an RTX initialization tunction. Characteristicssuchas the numberoftasls allowedto be executingwithin the s'ßtem,how often the operationis to switchfrom onetaskto another, and whether tasksare to run in a rcund robin or top to bottom (sometimescalledpreemptive or priority) fashion, are defined by the header.Since each subprogramstands somewhatalone,eachis given its own stackspaceto work in keepingthe processes truly independent.For example, Enb.dJe.t c Ldf,qdag. Tutatiat // PR RTX Contslo1 // Systen crystal frequeocy #define PR_xta1 t41 45600L [Hz] // Task switch Eine Inicroseconalsl +define PR switch Tine 5000 // Opelarinq node 1 = rounal lobin // 2 = priority +define PR,op node 2 // Set +define 1ow point PR_Stack in RAM for the Ran_Low Ox6O task stacks // Define the stack sizes for hhe alefautr task. these // ale optional defines. rf eirher is nor presents, rhe defautr // !a6k gets the sane defaulL srack sizes as rhe otsher rasks. +define PR defaulE-Eask dara-srack 40 +define PR default_Eask systen sLack aO // Define the naxinun nuid,ber of pR Max Tasks 10 +define rasks for // Define the prescaler +define PR Divisor_Type hype. See docs +include diviso! 1 ahe project. for deraits. "PR RTX Contsrot.c' Once the operational characteristics are defned, the RTX is initialized with definitions of what tasks you wish to have run and the priority you would like ro have the tasks assigned to. Priority is impo.tant in tÄat if for some reason a task could not complete its funation within the allocated amount of time, the RTX can rake the operation back to the highest priority task and start again.This allows for the important and generälly time critical tasks to get processortime no matter what is going on with lower priority or less important tast$. In the following example, two LEDs are being flashed by two independent ;sks. You wil seethat each task is simply wiaen as a C function ofqpe void and that each function contzins a.utbik(l) loop.This is becausethe functions do not retum to a caller-they are each running as stand-alone programs. void blnksrn { vo iat) I while (1) PoRTc _= 0x01; PR itait_Ticks {40) ; l //chaoge //wair green 2OO ns LED staie 73 blnkred void (woid) { unslgned DOPTC lwhile { char x = 255i 0x2; //sLarL //sLärr slow t,1ink dith ligh- on {1) ?oRTc ^= 0x02; PR Wair Ticks(x); x = 10; //changre real LED state //wair 500 ms //change to fasE blink after first blink J ) PR creare_task(0,b1Dkred,0,0,1) ; //start PR_Create_Tdsk(r,blntq'n,0,0, l); //sLdrl task 0 ldsk I t void // // mai! (void) Dec).te your locdl vdt idbles hetc I^puL/OutpuI Po Ls aiLidlizdlion // Patx c PORTC=0x00; DDRC=0x03; PR_RTX( ) ; //start RTx while{1) loop becones // The nain prog.an's or lowest priority task. // the 'default' while (1) { can t,e done here // oLher operations // if desi.ed. t 'default' or lowest-level task. The while(l) loop in the Anctror' na;nQ becomes the Since each task is responsible for rcleasing time back to the system using the PR-Wa;t-ncks0 tllncdon, that unused sptem time is nrneÄ o'vet to na;n). In a tlpical application development, the dow operations such zspr;ntfj ot scanfl) would be performed 'n to the ma;nQ arÄ f,.obal'ranables would be used to communicate needed infomation other tasls in the program- Entedded C Lakg"tX? T,tottt/ I.I2.3 STATEHACHINES State machines are a common method ofstucturing a program such that it never sits idre waiting for input. State maclines are generally coded in the form ofa switcVcase construcr, and flags are used to indicate when the processis to move fiom irs cunent state to its ncxr state. State machines also offer a befter opportunity to change the function and flow ofa program without a rcwrite, simply becausestates can be added, changed, and moved with out impacting the other statesthat sur.ound itSratemacJliresallow for rhe primary logicaloperationofa programro happenson-ewharin |erylitde rime is spenractualJyprocessingeachsrare.mo"e free 1,:Ig'9""d !'!*.)"'.zllv CPU time is left available for time-critical taskslike gathering analog-information, process_ ing serial^communicarions, arrd performing complex mathematics. The additio; CpU tlme rs otten de1'otedto communicating with humans: user interfaces, displays, kevboard services,data ent)! alarms, and paraneter editing_ Figures 1 1 and 1 2 show an example state machine used to control an .,imaginary'' traffrc llcnf. The.raren achinein rhisexampleusesPORTB ro drir,erhe red,qreen, andveUow.i!.hr.r rhe North-Sou r-hand Easr Wesr directions.N ore th^t n naid );he d qt.,z"17n nc"riont. used to control the time. This keepsthe example simple. In real tife, this time could be used for a myriad ofother tasks and functions, and the timing oftle lights could be controlled oy an interrupt from a hardware timer. Th€ state machine Dr-srardrl'l is called every sccond,but it executesonly a few instructions before retnrning to ;zaä Q.-fhe glob vtiable canerü nak controls the flow ofthe executior 'fhe thtough Do-Sta*s). PED xlNG_EW, pED ^fNG_NS, arÄ FOUR_WIy STOp mputs createexceptronsto the normal Ilow ofth€ machine by altering either the timing, the prth ofthe machine, or both. The arample system tunctions as a normal stoplight. The North-South light is green when the East-West light is red. The traffic is allowedto flow for thirty-seconä De;ds in each direction. There is a five-second yellow warning light during the change fro; , geen_light tr a red-light condition. If a pedestrian wishes t" .-"s th" fl"*ing t p;essing ;he "fic, PED XING_EWor PED XING-NS bunon will causetlc time remaining for traf6Jflr,* to-be slgrtened to no longer than ten seconds before changing diiedions. If the FOUR_WAY STOP stwltchis turned on, the lighr"la,ill corr.,.n on , ro ,ll four flashins red. Thi..conver.ion wiJJhappcn onJydur'Lngrhe waming (ye[ow) tighr tran.iLion to nir<e rr User interfaces, displaTs, kel.board services,data enry, alärmsJand paramerer editine can also be performed using state machircs. The more "thinly sliced; a program beämes through the use offags and states,the more real-time it is. Morc things are be;ng dealt with continuously without becoming stuck waiting for a condition to change. 75 76 6 ä + I'. ,J l ä -l ' _-t '*ä#Eä3*F$ä , $=$$$$äF ==3i*-" BB8tsgS 3 3 E I q) z I = I E I € i ltl { Enbedded C Lrrgüage #include #include <Meqa8515.h> <de1ay.h> +define E i-RED LITE poRTB-o +dEfiNE #define +define +define EW_GRN_LITE NS_RED_LITE NS_YEL_LITE Ns GRN LITE PORTB.2 poRTB.3 +define +define +define PED XINC Ew PINA-o PED-XINC Ns PINA-1 FOUR-WAY sTop prNÄ_l alefinirions to accual // // // /' /' pedestrian pedestrian /" svitch outpurs Llme ia seconds spent in each cntreat slare of rhe lighls tagsle useal fo! FLASHER srate Eli IIARNING // The actual state nachine void Do Stares {void) is ro the nachine each nane , NS_I4OVING , NS WARNING , FLASHER ], here.. i EW_MOVING: EW_GRN-LITE NS GRN_LITE Ns RED_LITE Ei.l RED_LITE EW YEL_LITE NS YEL I,ITE if{PED { = = = = = = 1; O; 1; 0; 0; 0; // east // north wesr has sourh XrNG EW ll FOOR WAY STOP) // pedestrian wishes to // a 4-way stop is required it (cine lefr > 10) = 10; tine left // rhe has sreea!! Lhe realtl shorren the Eine ) if(tine t left != 0) tine teft; .etsurn; Fiaurc l-2 tmogjnatyTtofrc Light Softworc(contim'es) r/ +/ */ srare switch(currenr sbate) case +/ push burton crossinq push burton crossing input fo! 4 way stöp This enunerarion creates a sinpte way to aalil stsales generatse an inteqer by name. Enune.ations value fo! autonaticaLty, making the code easier ro naintain. ENUM 1 Ei' MOVING , { /* PoRTB.4 PoRTB.5 char tine Left; inE current_state; char flash tossle; // // // Tttat;al // coünt down the tine // rerurn to main 77 78 CASE so. / / tine expired, \ = 5; tine left 5 seconds to waRNrNG // give = EW $TARNI\IG; curent sLafe // tihe expired, move break; // to -"he next scate EW I'IARNINC: Ei{_GRN_I-ITE = 0; = 0; NS-GRN-iJITE EIt_RED LITE Ew YEL LITE IIS YEL LITE if(lime lefl = O, = 1,. = 0,' l= tine_lef return; I if(FouR | 1 lrreak; CASE // and east-rest has // counr 0) the ye11or down lhe line E; waY sroP) current state / / // to nain // return tine expireal, so.. if 4-ray reqüesred rhen srar! = FLASHER; // the flasher // oEherwise. = 30; Eine_1efE // .tLee 30 seconds ro MoVTNG = NS_üOVING; current_stsale / / time expi' ed. mo\e // Lo Xtrc next state NS MOVING: EW GRN LITE NS_GRN_LITE NS_RED_LITe F!{_RED_LTTE EW_YEL_LITE NS_YEL_LITE = 0; = 1; O; - l; = 0; = 0; // // north souLh hds Lhe gleenll eösl west has Lhe _edl if{PED XING NS II FOUR !t]AY STOP} a pedestxian rishes to // it I // d 4 \|ay stop is lequiled.. > 10} if{line left = 10; time teft // shorten the tlne ) if (tine_fefE { != 0) // coun! down the --tine-left; ') return; line_1eft = 5; / / // fime qive to maln // return expiled, so, , 5 seconds tso j'ARNING (Contlnües) Fiaure l-2 ImosinsryTrufi. üst't SoFwsre Eime Enbedd.d = Ns waRNrNG,. currenr_stsale break; CASE NS_iIARNING: EW_GRN LITE NS_GRN LITE lüs_RED LITE ET{_RED.LITE EW YEL_IJITE NS YEI_LITE if{tine t = = = = = = teft O; O; 0; 1; 0; 1; != // no.rh-south // and tifre expired, nove to L]ne nex! srale // // has easr,west O) // C Lang"dge Tutaria! the has counr yellow., rhe red.. alown rhe rine -Line-fefr; recü.n; // return ro nain // Eine expiled, so.. if(FoUR_wAy sTOp) // if 4-ray requesreal lhen starr currenr statse = FLASHER; // the flasher j | ) break; // othetuise.. = 30; cine_1efc // si.!e 30 seconds to = EId üOVING; current-state tine // expired, nowe Lo E}re next // srate EW-CRN NS_GRN EI'_YEL NS_YEL LITE LITE LITE LITE = = = = 0; 0; O; 0,. // // a1t yetlow green lires ^= 1; flash_togqle if{ftash toggle & 1) // roqqte MoVTNG anal off LsB.. t NS_REDLrTE = 1, EW_RED LITE // blink reat lishrs = O; ] etse I NS RED_LrTE = 0; EW RED_LITE = 1; J if ( ! FOUR-rirAy_STOp ) currenr srate break; Figufe t-2 // alternarely // j,t \o loager a 4_way slop = EW_WARNING; // Ehen return ro normal Inosjnoryhofrc Ught Software(Contjnues) 79 80 culrent break; state // = NS WARNING; set any unknown state io a good onel l ] nain (voial) void I DDRB= oxFF; DDRA= 0x00; curren!_stale // // portb porta all att = NS_OARNING; out in // inlr'iarize to a qood startinef { delay ns(1000); // // | secoad delay-- this tine could t'e used for other neealed processes Do_Stales0; // // ca!! E}le slate nachine, it knows wbere iE is and ehar to do next l I Figure l-2 I.I 3 lmaginorylaffrc Dght Softwote(Contjnued) PROGRAMMING STYIE, STANDARDS, AND GUIDEIINES Using the C language to write sowce code is just part ofthe entire softwa-redevelopment process.Theie are many considerations that fall outside ofwriting the code arrd the desired operatior of a program. These considerations indude: . Readabilityand maintainabilityof tne sofalvare . A docum€nt€d develoDment Drocess . Projectmanatement . Qualitycontrolandmeetingoutsid€requir€ments suchaslSO900landlSO9003 . Configurationmanagementand revisioncontrol . Design-ruleandcode-stylerequirementsof your companyor organization . Verification andvalidationprocesses to meetmedicalandindustrialr€quir€m€nts ' Hazardanalysis As you begin to develop code for products and servicesthat are rcleasedinto the marketplace, these aspectswill become as much or more a paft ofthe de!€lopment prccessxs ffitting the actua.loperating software. Many companies har€ software "style guides" that de6ne Eflbedded C Langta{e Tutaridl how the software should be physically strucrured. Items such as header block fornrai, bracket and parenthesesplac€ment, naming conventions for variables and definitions, and rules for lariable types and usagewill be oudined. This may sound a bit ominous, but once you begin writing using a deined sg4e and developrnent criteria, you rvill 6nd it easier to collaborate and sharecffort with others in your orgarrization, and you rvill have fewer errors in your code from thc outset, as well. Organizations such asX1ISRA (]lotor Industry Software Reliabilit_vAssociation) ha\.e created documentsthat show horv following somebasicrules and guldelincsduring software development can greadl, improra the safetv and reliability ofthe developed software-and reducesomeofthe anno)'ing"got yah" npe errorsduring the developmcnr p roress.You can 6nd morc inlormation about these guideJinesat hnp://www.misra.ore.uV I.I4 CHAPTER SUMMARY This chapter has provided a foundation for you to bcgin writing C languagc progrnms. The beginning concepts demonstrated thc basic structure ofa C program. Variablcs, con stants,enumerations,their scopeand construction,both simple aswell as in aravs, struc tures,md unions,havebeenshown to bc usefulin defnjnu how memorl is ro bc allocateo and how rhedaLasirhin rl-rr memowi. ro be interprereLt Ly r C program. Expressionsand their operators,induding VO operations,werediscussedto providea basis for perlorming arithmetic operations and determining logical conditions. These operations and exprcssionswere also uscd with control constructs such aswhile and do/while loops, for loops,and switch/caseand itelse statementsro form funcrionsaswell assuide tbe florv of executlon m a program. The advancedconceptsofreal-time programning using intenupts executivesand state mrcJrineswere crplored to demonstratc how to streamlinc the erecution ofprograms, improve their readabiliq', and provide a timel)' control of tie processeswithin a C languageproject. l.l5 ExERCISES | . Define the terms vortobleandco,stort (Section| .4). *2. Createan appropriate de€larätion for the followinSGection| .4): ' A. A constäntcalled"x that will be serto 789. B. A variablecalled"fred"rharwill holdnumbersfrom 3 to 456. C. A variablecalled"sensorout" that will containnumbersfrom - | 0 to +45. D A variablearrayrhatwill haveten el€ments, eachholdingnumbersfrom 23 to 345. E. A characterstringconsranr thatwill cont in the strinS'Press herero end". Al 82 F A pointercalled"ärräy_pti'thät will pointto än äräy of numbersranging from 3 t6 567G. Usean enumeration to set"uno","dos",'1r€s"to 21,22,23,respectively. 3_ Evaluäte the following(Section1.6): A. unsigned charq t = 0x23* 2i I r= | B. unsigned int qt = 0x78/ 34; //t=l cha.xi x= 67Ai x= | C. unsigned D chard;d = 456; // d = ? E. enum{stäft = ll, otr,on,rone};/sone=l F x= oxc2ty= 0x2iz = x ^ Y Jtz= | G. e:oxtrede i =e>>4i lle= | l . f = 0 x 9 01 7 il l l = l x=l l. x= lziy=x+2tIy=2 Evaluate astrue or falseasif usedin a conditional statement(Section1.6): = = For all problems:x 0x45;y 0xc6 A. (x == 0x4s) B.(' lv) c.(">v) D (y 0x06== oxc) 5. Eväluatethe yalueof the variablesafter the frägmentof code runs (Section| .7): unsigned €harloop counq unsign€d int value= 0; for (loop-count= l23i loop-count< l3lJoop count++) //value= ?? Evaluate the valueofthe \"ariables aft€rthe fragmentof coderuns(Sedionl.4l = unsiSn€d charcntr l0; unsiSned int wlue = l0; t Enbedded C L'hgLage ] while (cntr < lo)i //value= ?? Tltori4! cntr = 1? 7. Evaluatethe mlue of the variablesafter the fragmentof code runs (Section| .7): unsigned charcntr = l0; unsigned int value= l0: while (cntr< t0) { value++; l cntr = ?? 8. Given:unsisned charnum_armyl] = { 1,2,3J,s,6,7,8,9,10, I I, l2}; (Se€tion1.9): i/ num arny[3] = ?? ll y^lüe = ?? 9. Giv€n:unsign€d int*ptr array;(Section1.9): unsiSnedint num_arrayl ] = {10,20,30,,{0,50,60,70h unsignedint )<,),; Ptr array = num-a ?yi x = *ptr_affäy++j y = *ptr_array++i llx= ll y=ll = ll ptr_array * | 0. Writ€ a frägmentof C code to declarean appropriat€arry and then frll the array with the powersof 2 from 2r to 26(Section1.4. I l. What doesthe acronymMISRAstandforl "*" preceding an exercisenumber indicates that the question is answered or partially answeredin the appendix. I. I6 LABORATORY ACTIVITIES A. Creat€,compileandtest a programto print"C Rul€sandAss€mbler Droolsl!"on the ständardoutDutdevice. B. Modit the programto usea for loopto printth€ samephräsefour times. C. RepeatusinSa while loopto printthe phrasethreetimes. D And yet ägainu$ng a do/while to print th€ phrasefive times. 83 84 the capaciqofa septictank.Thethreedimensions 2. Crearea proSrämto calculat€ heiSht, width,andl€n8thshouldbe readfrom threeparallelpons,\ B,andC (in feet) andthe result printed to th€ standardoutput device.Themaximumsthe program and25 fe€tof depth(itt a bi8 shouldhändleare50 feetof width,sofeetof length, variabl€sizesandusecaningwhererequiredto correctlycaltankl).Useappropriat€ andprint the resultasfollows(a y,z,andqq shouldbe the a€tual culatethe capacity The capacityof a tank x feet long by y fe€t highby z feet wide is qq cubicfeet of andstop. The programshouldrun once,printtheresults, the allowed 3. Modifythe programinActivity2 so that if anyofthe threeinputsexc€€ds nnge, the ProSnm says ' - am -angö ' 4. Creat€ a proSram to print tlle powers of 2 from 20 to 2r'?. readsport A and 5. Usea switch/caseconstructto cr€atea prognmthät continuously providesoütputto port B according to the followingtable: 0r00 ü.01 ü.02 OJ.O3 0.04 OJO5 oo6 (M)7 0b00000000 0b00001111 0b11110000 0b01010101 0b10101010 0b11000011 0b00111100 0b10000001 0b11111111 accordinS to the 5. Createa programto determinethe orderof storägeoflongvariables suggestion in the"StructuresandUnions"section(Section| . |0) relativeto unions lnearthe middleof the section). 7. Create a prognm d'at cansearchan arräyof structuresfor specific\alues-Declarean "rnonth", "doy'',and"y€or".Initialize the the members arrayof structurescontaining your However. the month, contäin one and only one instan.e of own birthday. arrayto day.andyearof your binhdaymustshowup in other placesin th€ array,just not all at the samepointThepro8rammustsearchthe arrayto findyour binhdayandthen print a messageto indicateat what index in the ärräyth€ binhday resides. 8. l',1odit the programin Activity 7 to searchthe array of structuresusingPointers. Enbedded C Langtage Tttarirl 9. Createa progrämto usetie standardinpüt function g€&hod to r€triev€ one character and compareirs valueto tie ralu€ placedon portA lf they match,print a m€ssäge to that eff€ct on the standardoutput deviceusin8prinaf0.Otherwise,output a 0x0 | to Port B if portA is higherin valueth:n the charrcter received,or output an 0x80 if | 0. Us€an external hardwareinterrupt to prirt a messageto the ständärdoutput devi€e eachtime an interrüpt occurs.Also print the numberof times the interrupt has occorred.Youmoynot usea Slobalyariableto count rhe irrerrupt occurr€nces. 85 The Atmel RISC Processors 2.t oBJECTIVES At the conclusion of this chapter, rrcu should be able to: . Define,describethe usesoi and identifythe m€mory spacesand r€gistersof the RISCmicrocontrollers . Allocrte the mi€rocontroller resourcesto ä projecr ' Apply int€rrupts to C programs . Write C programsto completesimple l/O tasks . Apply the major peripherälsoftheAVR microcontrolleß to solve problemsin interfacingto el€ctronicdevices . Write C programsto accomplishs€rialcommunication . Readand determin€ the resultJofAVR assemblylanguageprograms 2.2, INTRODUCTION This chapter provides most of the hardware background needed by an engineer to successlirllyapply the Atmel AVR RISC microcontrollers to a problem. It is based on the premise that in order to be successftl, designers must be as intimately familiar with the hardware as they are with the programming language. The chapter begins with the basic oven iew ofthe processor,its architecture, and its functions. Next, the rnemory spacesare discussedin detail so that you can identi$' and understand where 1'our variables are stored and rvhy. The uses of interrupts are next discussed,along with the most common built-in peripherals. These topics are then combined into the processof allocating processorresourcesfor a project. A variety of the peipherals common to many of the Atmel microcontrollers are discussed. Many of the Atmel para have additional peripherals or ertended a7 88 functionality in their peripherals. Consult the specification for your pafticular pait to d1s cover the full nnge of peripheral functionality for your particular microcontrollcr Each of the pcripherals is shown as it applies to projects- Lasdy, assemblvlanguageis described as rt pertains to understnnding th€ microcontroller's functions. 2.3 ARCHITECTURAL OVERVIEW The microcontrollers being considered are the Atmel A\rR RISC microcontrollers. This one sentencesals volumes about the architecture ofthe devices. First, they are RISC devices. RISC stands for leduced instruction set computing" and meansthat the devices,re designedto run very fast through the use ofa reduced number of machine-level insüuctions. This reduced number ofinscuctions contributes to the speed due to the fact that, with a limited number ofmachine instructions, most can run in a single rycle of the processor clock In terms of MIPS (millions ofinstructions per second), this means that an A\rR processorusing an 8 MHz dock can execute nearly 8 million instructions per second,a speedof nearly8 MIPS. Secondly,the devicesare niracantrollers- A mlctocontoller is a complete computer slßtem optimized for hardware control that encapsulatesthe entire prccessor, memory and all of the I/O peripherals on a single piece of silicon. Being on thc same piece ofsilicon means that speedis once again enharrced,becauseinternal I/O periphcrals take less time to read or write than external devicesdo. Being optimized for hardware control meansthat the machine-level instruction set provides convenient insfructions to allow casy contol ofVO devices-thue will be instructions to a11owsetting, clearing, or interrogating a single bit ofa parallel I/O port or a register The ability to set or clear a bit is g?ically used to tum a hardware device off or on- In a p(ocessor not optimized for hardwre control, the setting, cleaing, or reading ofthe individual bits of an I/O port (or any other rcgister) wornd requne additional AND, OR, XOR, or other instructions to affect a single bit ofthe portAs an axample,consider the following code fragment that sets the third bit of Port A high: PORTA=PORTAiOx4; \Älhile this linc of code is conect for usewith either a standard microprccessor or a micro controller, the actual results are different for the two dcvices. The following snippet shows some assemblycode generated for a standrrd microcomputer and for a microcontroller to cxecute the line shor,lrrabove: Standa!d nicroconputer IN R 3 O ,O X 1 B MOV R2 6, R30 r , D r R l 0 , L o w ( 4) oR Rl0, R26 OUT 0x18.R30 : Proet:r: .Tbe,4tnel.RISC MacrocoaEroller: sBr 0x18,2 As these cramples demonstrate, the standard microproccssor shoü,n tales nve instructions to set the bit high while the microcontroller täkes onl,r, one. This equates to a 6ve times speedincreasefor port operations in th€ microcontroller and a 6ve rimes decreasein code size for thesc operations. Microcontrollers allow for reduced code size and increasederecution speedby providing instructions that ,re direcdy applicable to hardware control. Overall, the architecture of the Atmel AVR devicesis that of a microcomputer It is orga nized into a CPU (cenual processingunit), a memory and an l/O section.The CPU is masked *om our vision, but the memory and VO sections are very visible and need to be understood by the applications designer Each ofthese is discussedbelow. 2.4 MEMORY The memory section ofthe Atmel RISC AVR processorsis based on the Harvard moocr, in which wrious portions ofthe memory äre separatedto allow faster accessand increased capaciry The CPU has a separateinterface for the FLASH code memory section, the data memory section,and tie EEPROM memory scction,ifone is present. The actual memory being discussedis that ofthe medium sized microcontrollers such as the AIMega16. Check the specification ofyour particular microcontroller to s€c the exact memory coon$llaüon ror your Par. ?.4.I FLASH CODE MEHORY The FI-ASH code mcmory section is a block of FI-ASH mcmory that starts at location 0d000 and is of a size that is dependenr on the particuta Atmel AVR microcontroller in use.The FLASH code menory is non-volaile nemory (retains its data even when power rs removedl,and ir i. u,edto srorer he cxccurablecodeand consrants. becau,erhevmu,t remain ir rhe menory even when pouer is removedfrom rhe device.The codF memür) \pace . 16 bits wide at eachlocatior to hold the machine-levelinsmrcrionsthat aregpicaLiyi single 16-bit word. Figrre 2-1 shows the menory map for the FLASH section of memory AJthough the FLASH memory can be programmed and reprogrammed with erecutable code, there is no provision to write to the FI-ASH by means ofan executableprogram; rt must be programmed by extemäI means. Consequendy, it is viewed as read-only memory ftom the programmer's perspective and is therefore used only to store constant rype var; rb1es,along with the executablecodc. Constants are automatically promoted to int siz€ vanableswhen thev are stored in FLASH code memory spacebecauseof the memory width. 2.4.2 DATA MEMORY The data memory of thc Atmel AVR proccssor gpicaly contains thrce separate areasof read/write (R V) memory The lowest section contains the thirry two general-purpose working rcgisters, followed by the sirty-four VO registers,which are then followed by the internal SRAM. -a9.. 90 T"p + Figu}e2-l "Imrm"rl dt"t nJ' u mrturon,tuUcr lryc 16 biß side + FIASHCodeMenory The general-purpose working registers are just that they ?re used for the storage of local variables and other temporary dau used by the program whne it is executing, and they can even be used lor the storage ofgtobal variables-The sixg-four I/O registers are used as the interface to the I/O devicesand peripherals on board the microcontroller And the internal SR-AM is used as a general variables storage areaand also for the processorstack. The memory nap for the data memory areais shown in Figure 2-2. Registers The general purpose worhng registers occupy the lowest thirty two cells in the data mem ory These registersare used nuch like the storagelocations in a calculator, in that they store temporary or intermediate results. Sometimes they are used to store local variables, some times global variables, and sometimes the pointers into memory that are used by the procer sor In short, the processor usesthese thii:ty-two working registers as it erecutes the program. The use of the thirty-two working registers is controlled by the C compiler and ß g?ically out ofthe programmer's control unless assemblylarguage is being used. I/O Registers In an AIMega16, the VO worhng registen occupy the next highest sixty-four byes in the data memory space(refer to Figure 2-2). Each ofthese registers provides accessto the con trol registersor the data registersofthe VO peripherals cortaircd within the microcontroller. The tlmet +E, RISC Pfat.$o/t d !i slL{v dcr.n{ onmoo o,rpu(h?r +LOa d:rüh m c m o ^r d d r . . 0 . 5 I r 1 O r . s r _ ( r 0 .r F l 61 6d Egnrß usd b nftr.;i< +I/O ltft +c€nern r d?h mcmoa-addre$0xr0 (ro Eg{q 1) PüJlnr R€nc6 cßdrt 0r01F i2 tdri :cDüd turyo{ 3 bir nmd Purportu$€. + Figorc 7-2 $m d 0x000 3 bns{ide + DotaMenotyof theATMegal6 The programmer usesthe I/O registcrs extensivelyto providc interhce to the I/O peripher als ofthe microcontroller Other Atmel devicessuch as the ATMeea128 have more I/O registersthen will ät in the 64-bytespacc.These devicesoccupyspace up ro 0x100ro accommodate thc larger number ofllO rcgisters. In Chapter 1, "Embedded C Language Tutorial," you have already seen examplesusing the I/O registers called PORTA and DDRA. Thcse VO registers were used in the examples relative to writing to and reading from a parallel port- Figure 2 3 shows a selection ofthe I/O registers,cmphasizing those associatedwith rhe parallel ports. uo O SRÄ,lvI DDRÄ Data DftLtion Registerfor Porr A DDRB 0tt7 0x37 Data Di.€dion Registerfor Port B PORfA 0)<18 0x3B Ou9ut Lxtches for Port A PINB 0x16 0^lö SREG 0^rF 0^5F Figure 2-3 Exdmplel/O registers Prcce$or Statxs Registü 9l 92 Each I/O register has a :rame, an VO address,and an SRAM address.A C language programmer will nost commonly use the VO register name. The two different numeric adilrcssesare important when witing in assemblylanguage becausesomc of the instructrons relate to the SRAM address arrd some relate to the VO address.For further informatron 'The AVR RISC xbout the AVR instruction set and assemblylanguage, see Section 2.12, Assembly Language Instruction Set-" The I/O register names are much more convenient for thc C language programmer to use than the addresses.Hon"ever, the C languag€ compiler does not inherendy know what these names are or know what addressesto associatewith the names. Each program contains a #include header fle that defines the names and the associatedaddressesfor the C language compiler. The header file* were detailed in the Chapter 1, "Embedded C Language Tutorial." The C language progrun in Figure 2-4 demonstrates these concepts. t DDRA = OXFF; t'its of Ports a are /iAll DDRB = 0x00; biEs are inpuEr/ /'aII whi te (1) t B anal srite PORTA = PINB; /*reaal port output*/ to Port A*/ ) FiBure 7A Pottlnirjalizdtio,usi,4gRegister Nomes This program readsthe pins ofPort B using the PINB I/O register and writes the results to the output latches ofPon A using the PORTA register.The C compiler gets the addresses to use with these register names ftom the #include header file in the lirst line of the pro gram, in this arampte, mega16.h. In summary, the C languag€ programmer usesthe VO registers as the intedace to the I/O hardware deviceswithin the microcontroller- Subsequent sections of this chapter descibe the use and function ofeach ofthe VO peripherals in the microcontroller and their associated I/O registers. SRAM The SRÄM section ofmemory is usedto store vrriables that do not 6t into the registers and to store tle processorrtzcn-Figue 2-5 shows the SRAM section of data memory As Figure 2 5 shorm, there are no special areasor ahvisionsof memory within the SR-AM. The addressesshown in this figure are those for the SRAM section; their physicat addresses will not be the same. Data is usually stored staning at the boftom ofthe SRAM, and the Vocessor starAor stack start at the top of memory and utilize memory from the top down. Tle Atbe/ RISC Pntüsarl Top of Ilrmory depeftls on misosn@Uer + Figur€ 2-5 rlT. 8 bi6 widc + SRA^.4 Sectionof DataMenory The processoruses the sta& area of memory as temporary storage for function return addresses,intermediate results ftom calculations, and any other shorr-term temporary data storage.The CodeVisionA\R C language compiler actuälly implements two stacks:The slstem stack st^rts zt the top of the SRAM area and is used to storc return addressesaqd processor control informatton.The data Xa& stars bdow the system stack and works lts \d"y down through memory in a manner similar to the system sraclq and is used to store temporary data, such as the local rariables used in a function. While the use ofthe SRAM memory for data storage is fairly straighdorward, its use for the stack is not. The stack may be thought ofas art area ofmemory set aside for temporary storage,much as a spot on your deskwould be set aside for the storage ofpapeß. New dara (or a new piece ofpaper) ts ?L'hed onro d\e st?.chand old data (or the rop piece ofpaper) is ?a?pedoff the stackÄ a ZIFO (last in, 6rst out) manneL't\e stac(po;nter (SP) holds the addressofthe memory cell that is currendy available for use. The stack pointer keeps track ofthe ns.t available locatior to store dxta onto the stack. It works as follows: | . When new datä is readyto be placedonto the stack,the processorusesthe SPto lind where in memory ro placethe datä.For example,if the SPcontainsthe value 0x200,the datawill be plac€din SMM memory location 0x200. 2. The SPis thendecremented to locationoxlFEandthe processorbeginsto execute the next instructionln thismanneitheSPalwayscontains the locationofthe nexr memorycellofthe srackthat is available to be used. At some later point, the processor may want to retrieve the last piecc of data pushed onto the stack.The retrieval processrvorks as follows: | . Wh€nthe processoris readyto retrieveor pop dataoff the stack.it readsthe SPand immediately increments th€ SPcontentsby one.Since rhe stackpointeris alMys pointintto the next availa-ble (empty)locationon the stack,incrementintthe stäck pointermeansthat the addressnow in the stackpointeris the addressofthe last usedlocationthat containsdata2. The processorusesthe addr€ssin dre SPto popor retri€vethe datafrom the stack. Sincethe datahasbeenretri€vedfrcm this location. its addressis left in the SPas beingthe nextavailable locationon t]|e stack.Thenextbyte pushedonto the deck will oveBrite the datathat waspresenrat that location. Stack operations are summaized in Figure 2-6. The major concept relative to the stacLis that asdata is pushed onto the stack, the stack uses progessively more memory in the SRAM area,starting at the top of SRAM and worhng dorvnward. As data is popped off the stac\ the memory that has been previously used is re lea.ed.and the availablc stacklocationmovesup in memorv. Likewise, the data stack is located in SRAM below the sptem stack.The aract location is set by the programmer in the compiler confguration settings. The data stack worli:s vcry much like the system stac\ using a data stack pointer just like the svstem stack pointer, growing downward through mcmory as it is used and back upward as it is released. Global variables may also be stored in the SRAM m€mory aJeastarting abovethe I/O register area.The SRAI4 is used in an upward direction until spaceis made available for the global variablcs. It is the programmert responsibility to ensure that the system stack does not come down lolv enough in SRAM to overwrite the data stack and that the data stach does not come down lorv enough in memory to overwrite the global variables area.In nost cases,the compiler takes care of thcsc limits, but ultimätely it is the rcsponsibiliqv of the programmcr. 2.4.3 EEPROMl.IEMORY The EEPROM section of memory is an area of read/write memory that is non volatile. It is g?ically used to storc data that must not bc lost when porver is removed and then rerpplied to the microconaoller. The EEPROIVI spacestarts at 0x000 and gocs up to a maxlmum value that is dependent on the specific microcontroller in use. Although the EEPROM section of memory may be both read and written, it is seldom used for general variable storage.The reasonis that EEPROIVI memory is very slow to write; rr Th. Attel Purhing dato oDto the std.k Popting dd2d fton the no<k SRAM SPnqM 0x25F SP: ox25E OX25D 0x25C OX25B OX25A OX25F OX25E OX25D OX25C ot25B 0x254 Fißt steo: Wrhe n€wdoto SRAM SP: RISC Procetsols E nn+; lr.Emert SP SR]\M 0x25F SP: 0x25E OX25D ox25C OX25B 0x254 0x25F 0x25E 0x25D OX25C 0x258 0x254 SRAM SRAM OX25F SP: OX25E 0x25D ox25C OX25B ox25A 0x25F 0x25E 0x25D 0x25C 0x25B 0x254 Noter AI ofihe cells mdkcd "aEilable" adually ontain some data. Either it omes fron whatder ws there at power u!, or it may be data pftviously on the stäcL But rhc data is no longer needed od so the cels de auilable to Mite ns dzta into. Figure 2-6 StsckOperotions can take up to on€ millisecond to complete a write operation on one blte of memory The e.(ensive use ofthis memory for variable stonge would slow the processordown appreciably. AJso, EEPROM memory can withstand only a limited number ofwrite cydes, as was mentiooed in Chrptff 1- So, for these reasons,EEPROM memory is usually reserved for those \'?riables that must maintain their rdue in the event ofa power loss. 96 Chapter 2 Example Proiectr PartA This is the 6rst part of a project eyample that will be used to funher demonstrate the con cepts presentedin Chapter 2.The example project will center on a data collection systemfor a .Lockca; accordingto rhe folJowingscenario: Assume that your boss hands you a data collection s)'stembased on an Atmel AIMegal6 microcontroller. He erplains that this system was designed to collect data for a drag racer over their Sfteen sccond flln, but that he would Iike 1ou to modi! the s]'stem to collcct data once per second over an entire two-minut€ lap for his stock crr. The collected data is then uploaded to a PC lor analysis-The system was originally designed to record engine rpm based on a pulse ftom one spark plug, drive shaft rpm from a magnetic sensor reading a magnet attached to the drir.e shaft, and engine temperaturc ftom an RTD thermocouplc attached at the cylinder head.Your boss explains that he ticd to have the progrrmming modi6ed once before, but, unfortunately, the inept programmer succccdedonly in errsing the entire progam. Happily for 1.ou,this meansthat all of the conditioning circuitry for the cn gine signals exists and tbat vou need only to provide a prcgtarn to collect the data and scnd it to the PC. The frrst task for you is to verify that the processor has suffrcient resourccs to do the job. First, we verifr that the memory is big enoughto hold the data nnd proc€ssorvariables. The data is to be saved every second for two minutes, so the number ofsets of data is as folowsl 2 * 60 seconds/minute* 1 dataset/second= 120 setsofdata So what you now need to kaow is the number ofbytes in each set ofdata. According to your boss,enginerpm is in the range of2000 to 10,000,shaft rpm is in the range of 1000 to 2000, and engine temperature is in the range of 100'F to 250'F. Your boss specifiesthat he wants rpm accurateto 1 rpm and temperatü€ accurateto 1"F. Therefore, you will be storing two integer sized numbers (two bltes each lor a total offour bytes) for the two rpm readings and one bne sizc number for the temperature in cach set of data. The total storage neededis as follows: 120 sets ofdata . 5 b1'tes/set= 600 b)'tes In addition to the data storagc, 1ou will need about twenty fu'e btes for ^ tlstem rta& ^nd torrybyres lor ^ data star*. (As you progressin your programming prowess,you will leffn to judge the size of stack required; in general, the more math you do and the more functions you nest, the more stack you will necd.) Checking the ATMegal6 spccification, you ots cover that the microcontroller has 1024 bytes of SRArV memon', and so the memory re sourcesare sufEc.ientfor the task. Normälly, at this point, you would also consider whether the peripherrl resourcesare sullicient as well. ln this case,howcrer, ),ou dont know about the peripherrls yet, and besides, the system worked for drag racers, so the peripheral re sourcesmust be there. Tbe .4td.l RISC Prcte)'orl 2.5 RESET AND TNTERRUPT FUNCTIONS Interupts, as discussedin Chaptcr 1, "Embedded C LanguageTutorial," are essentinlly hardware-generatedfunction calls.The pu+ose ofthis section is to dcscribe how the interrupt. tunct:on ard hos 'e.er,*hich is a spetial interrupt, tuncrions. Interrnpts, as their name $ggests, ;nttrtu?t the flow ofthe processorprogram and causeit to bta;\ch to an interrupt leruie routine QSR) that doeswhatever is supposedto happen when the interrupt occurc. Interrupts äre useful for those situations in which the processormust immediately respond to the inteIrupr or in those caseswhere it is very rvastefulfor the processor to poll for an event to occur. Eramples ofthe need for immediate responseinclude usirrg inteüupts to keep track of time (the interrupt may provide a ti& for the dock's time base)or an emergencyoffbutton th^r ;nnediateb stopsa machine rvhen an emergencyoccurs. Examples ofthe other useful applications ofinterrupts include deviceslike kelpads or other input devices.In terns ofthe microcontrollert abiJity to process insmrctions, we hurrans are very very slow. It would be wastetul for the processorto poll a keypad in hopes that one of us slow humans has presseda key. In this instance, the pressing of a key might causean interupt and the microcontroller would then briefly pauseto seeif the key press required it to do anlthing. Ifthe key prcssw€rc th€ 6rst ofseverat required to causean action to occur, the processorwould return to its tasksuntil enough kels had been pressedto require action. Using interrupts frees the processor fiom polling the kelpad constandy at a rate that is much, much fastcr than we can press the ke),s. AJI ofthe interrupts, induding /.rcr, tunction in exacdy the salrre marner. Each intenupt has a vector addressassignedto it low in program memory The compiler placesthe startirrg addressofthe associatedinterupt servicc routine and a relative jurnp instmction at the vec tor location for each interrupt. When the intenupt occurs, the program compl€tes execur ing its curent instruction and then branches to the vector location associatedwith that in terupt. The program then executcs the relatii'e jump instruction to the ISR and begins executingit. Whcn the internrpt occurs, the fttam a.ldrcls (the addressofthe next instruction to be executed when the interrupt is 6nished) is storcd on the systenstatA.^fhelast instruction iü the interrupt service routine is an RETI assemblylanguage instruction, whl,ch \s a retumfram interru2t.This rnstnctton catrsestheret m addressto be popped offthe stack and program execution to continue from the point at whicl it was intemrpted. In the AVR processors,all interrupts have the samc priority. There is no allowance for one intefupt to interrupt another interrupt, that is, one interrupt cannot have priority over another interupt. It is possible, however,for two intcrrupts to occur simultaneoudy. An arbi tration scheme,sometimes refened to as?r;oitf, is provided to determine which interupt executesin these cases.In caseswhere two interrupts occur simultaneously, the interrupt with the lowest numbered vector will be cxecuted6ßt. Refer to the vector table in the nerr section or in the specifcation for a specific processol 9A 2.5.I INTERRUPTS Figure2-7 showsthe tust six intenupt sourcesavailablein an AIMega16. The choicesfor interrupt sourcesand their vectorswill dependon the Focessorbeingused. 5to.titrg 0x0000 0x0002 0x0004 Oxo006 rlatmal r€se! Porcr up,W.tchdog timcout Occm on a hrd.w+ignal l Oc(]ß on a hddMre sign,.lon pin INT1 on p n INT0 Ocrus on a Tiner 2 compare matci llx{1)08 FiBure 2-7 2 5 Timer 2 Overflow Oc(u on m derndv ofTimer 2 SonqlelnkiuqtUe.aoß Interrupts must be initiäIized before they become active, or usable.Initializing interupts is a two-step process:The fust step is to unmask the intenupts that are to be active, and the second step is to globally enable all of the umrasked intermpts. Unmasking amounts to setting a 1 in the control register bit that correspondsto the intcrrupt that is to be used. For instance, the generalinteüu?t cont,ol reg;ner (GICR) register rs shown in Fizure 2-8. Bltt 7 Bit 6 Bit 5 INTl INTO INT2 \ Bit 4 Bit l \ mck bit ror *te-ar i'tc-pt \ masLbit for demal int€npt 0 Bit 2 Bnl Bir0 2 mi5kbit forqrcmal intemlt I Figur€ 2-8 6lCR GICR is used to enable the externnl interupts. As an example,setting the INT0 bit w l enable external interupt 0 (an arternal hardware signal appJiedto the pin that 1salso named INT0), or seaing the INT1 bit wiLI enable external intemrpt 1. Sening both bits will enable both interupts. The mask bits are used as c<acdy that, a mask. When an appropriate hardware signal occurs on INT1, for instance, that signal is logically ANDed with the INT1 bit in GICR.Ifthe result is a 1, the interupt may be allowedto occur (seethe following paragraphs), but if the INT1 bit in GICR is set to 0, then the result ofthe logical AND is always 0, and the intenupt wifl never be alowed to occur. Setting the inteffupt mask bit is necessaryfor an interrupt to be allowed to occur :::::::::::L: The second step to enable an interrupt is to set the global intemrpt enable bit in the #dlrr regrirer (SREG) ofthe processor.This is accomplished as follows: +asn("sei') This line of code is inserted in a C language progam at the point where you want to enable the global intenupt bit. This line uses a compiler directive, "#asm", to insert in the program the assemblylanguage instruction SEd the instruction to set the global interrupt enablebit. When an interupt occurs, the intemrpt signal is first logically ANDed with the mäsk bit from the control register appropriate to that particular int€rrup! and the rcsult is then logically ANDed with the global intenupt enablebit. Ifthe result ofall ofthis is a logic 1, then the interupt is allowed to occur and the processorvectors to the appropriate addressin the interrupt vector table. The program/hardwarc example in Figur€ 2 9 illustrates the use of external interrupt 0. +incLude inteüupt <meqa16.h> IExT INTo] woid PORTC = PORTC ^ 0x1; vold exE iElo /ttoqrqrle isr(woial) the LSB of port c*/ nain (woid) { DDRc=oxo1r GrcR=0x40; McucR=oxo2; +asn( Figurez-g sei /*port c LsB set for oulpur*/ 0*/ /*seE the rNTo biE Eo enable exlerna1 inter.upt on a fallidg edge*/ the rsc01 Eo activate /'set ) /'enable /*do nothlnS the - the s1oba1 intetupt interrupt does enable lL bit*/ atl*/ lnteluptE omplePn'gan This program toggles the LED attached to Port C, bit 0, each time the pushbutton aftached to the INT0 pin is pressed.Figure 2-10 shows tlre hardware setup for this program. Looking at the program critically, $,e seethat the #indude statement in the 6rst line defines the regist€/s and intenupt vecton for an AfMegal6 microcontroller. The next four lines are the intenupt service routin€ (ISR) for Extemal Interrupt 0- Notice that the 6rst line of the ISR, the function declaration, begins with the reservedword interrupt to tell the compiler that the following firnction is an intemrpt sewiceroutine- The compiler usesthis information to know that the register contents must be savedarld restored by the function (by pushing 100 AOCT|PAT ADC6/PA6 AOC'PA5 AOC4PA4 ADCSIPA3 ADA2IPpC ADC1/PA1 ArcO/PAO RESEI VCC AVCC AREF SCKPBT M|SO/PB6 MOS/PBs ss/PB4 oco/AtNl/PB3 ]NT/A]NO/PB2 T'PB1 xclvr0/PB0 XTALI XTAL2 AGND GND aazFDT ICP'PD6 oclL/PDs OC1B/PD4 INT'PDO tNTo/PO2 TXD/PDI RXD/PDO TOSCzPCT TOSCI/PC6 TDI/PC5 TDO/PC4 TMS/PC3 lCKtPC2 SD&PC1 scuPc0 Figure 2- | 0 InterruptProgromHardwore them onto the data stack at the start ofthe function and by popping them off the data stack at the end of the function) and that the function must end with an RETI instruction rather than an RET instruction. The " luxt_ruto l " definition comesfrom the #include file and amountsto the number 2, becauseExternal Interrupt 0 has2 asits vector number.The compiler usesthis information to placethe relativejump to the ISR function at the appropriateplacein the interrupt vector table.The balanceofthe function declarationis a normal one. The third line ofthe ISR is the activeline in the ISR. It usesan exclusiveOR to toggle the leastsignificantbit of Port A eachtime it is executed. In the first line of the main) function, the least significant bit of Port C is set for output. The following line sets the interrupt mask bit in GICR to allow External Interupt 0 to function when the global intemrpt enablebit is set.The next line setsthe Interrupt Sense bits in the MCU control regisrer(MCUCR) so that External Interrupt 0 is triggered by a falling edge applied to INTO. The Interupt Sensebits for externalinterupts 0 and 1 are shown alons with their definitions in Fizure 2-11. T h . , 4t n el R I SC P r a . e r a) ß Bir 6 Bit 7 Bit 5 BT4 Bn2 Bit 1 Bit0 ISClr ßc10 ISCOl tsc00 ?-==4 sense cont'olbirsfor qrmal t*^f senseonüol B,tJ bits for d\temal irterropt 0 ,scr, 0 0 Inrcrupt x is trig€red by a low leve1 I Inrcroptx is triggeredby an).chmge in l%ic ldel Inteftpt x is lriggü€d b,ya f'xing edg€ I I .I Intmpt x js üjggmd b) r d sing .dgc Figure 2-f I MCUCRlnlfnupt SeßeControlNß The "+asn ( " sei " ) " line is an assemblylanguageinstruction, ,SetEnable lnterrupt, which sets the global int€fiupt enable bit so that a falling edge applied to INT0 will causethe 'while interrupt to occur and toggle the LED- The tt)" in the nain) function does nothing exceptkeepthe proce"sorbu'y untii the inrerrupl occurs. 2,5.2 RESET R6rl is the lowest rumbered interupt It is also a special intenupt in that it always takes precedenceover all executing inteffupts and aoy code that may be runring. Three sources can causea reset to occur: a logic low applied to the extemal reset pin for greater than 50 nsr as a part ofthe power-on sequenceofthe microcontroller, and by a timeout ofthe watchdog timer Resetis used to preset the microcontroller to a known state so that it can start executrng the program located at location ü10000 in code memory The microcontroller state following a reset will vary slighdy depending on the processor being used, but it is essentially the following: . All peripherals (in(ludinS the wätchdoS timer)aredisabled. . All pat?llelportsare setto input . All interruptsare disabl€d. By disabling all the periph€räls and intenupts, the microcontroller can begin executing the program without unerpected jumps due to interupts or periph€rals that might causeunex pected or enatic behavior Setting the parallel ports to in? / node ensle;ies rhat a port and an externa.ldevice will not be tying to drile a port pin to opposite levels, which could damage t0l t02 Watchdog Timer and Reset The watchdog timer is a safety device. It is designed to causea processorreset in the case where the processoris lost or confired or doing anything other thar running the program it is supposedto be running. The watchdog timer is a tirner that causesa processorrcset to occur ifit is allowed to time out. When a progtam is operating normally, the progam consistendy reloads or resetsthe watchdog timer to prevent a timeout- As long as the program is operating normally and resets the *?tchdog timer, the processorreset will not occur, but if the program gets lost or gets hung somewhere,the timeout will occur and the processorwill be reset.The theory $ that a reset ofthe prccessorwill get the program back to operating normally. Figure 2-12 shows the bits of the Ilaxhdog t;ner untrol register,WDTCR. Bir 6 Bit 7 Bir(s) WDTOE WDE Bit 5 Bir 4 Bit 3 Bit 2 Bir l tsit0 WDTOD \VDE \\.DP2 \4DPI \\DPtl watchdog Tiner Otr Enable wat ndog Tind Enabre WarchdogPGcalü Bit x Figure 2- f2 Äxows disbljns the UDT Enablesthe WatchdogTimer Sctsthe timeout period for the $DT Wokhdogfinet ContlolReg:ßtqWDTCR The oscillator that clocks the watchdog timer is separate fiom the system clock. Its lrequency is dependent on the voltage applied to the processor.With 5 V applied to Vcc, the frequency is approximately 1 MHz This creates a situation in which, although the Watchdog Prescaler Bits in \Ä/DTCR are set to determine rhe timeout, the actual time rt takes to time out will also depend on the Vcc applied to the proc€ssor.Figure 2-13 shows the approximate timeout periods determined by the watchdog prescaler bits at two levels The times shom in Figure 2 13 are approximite, becausethe oscillator frequency is approxinate and dependson the €xactvoltage applied to Vcc- The program and circuit in Figure 2-14 denonstrates the use ofthe watchdog timerThe program and hardware in Figue 2-14 demonstrate the use of the watchdog timer. When the program starts, it hangs in the 6rst ?r, ile)loop wüang fot the pushbutton to be The z4tnel RISC Prares!ar! rime out @ 3VY<. Time out @ 5V Y.. I 0 0 I 0 .I .I 1 0 0 0 I I 520 ns 1 I 0 1000ms 1000ns 1 I I 2100 ms 2200 ms 130ms 260ms Note: Times sh@r m apprdiute. Figure 2- | 3 WatchdogTineout Peiod Seledion <nesa16.h> #include static unsigned lnt void { nain 'wdi- to /*variable tine blinks*/ (void) D D R C= o x l ; thile walter; / * s e L P o R T c . of o r o u t p u t * / fo! burron !o (PINA.0 == 1) be plpssed'/ { ; /*wait for PB to be pressedr/ l I , t D T c R= 0 x 0 b ; /*enable rcDToith /*stay in this loop while while (PINA.0 == 0) burton 130 ns tineoür*/ is held*/ +asm("wdr"); /treset ItT continuouslyr/ ++waiter; waiter wariablei/ / rincrenent i f ( w a i t e r = = 5 0 0 0 0) { port bit*/ PORTC.o = PORTC.o ^ 1; /-conplenent waiLer = 0; /*reset walter foi next alelay tine*/ l t while(1); l Fizure 2-14 /*lock up to allow liDT to tine WDT Ptoson E ompte (Continues) outt/ 103 t04 RESET vcc AVCC AREF XTALI XTAL2 AGND GND ADCTIPAT ADC6/PA6 ADC5/PA5 A0c4/PA4 AOCSPA3 ADC2PA2 ADcl/PA1 ADCO/PAO sct(P87 lvlSO/PB6 MOS/PBs ssrP84 oco/AtN't/PB3 INTZAINO/PB2 T1lPB1 XCK,/TO/PBO OCZPDT ICP'PD6 ocl pJPD5 OC1B/PD4 INTl/PD3 INTO/PD2 I)(D/PD1 RXD/PDO TOSC2/PCT TOSCl/pC6 TD/PC5 TDO/PC4 TIVS/PC3 TCK]PC2 SDI/PC1 scuPco IEGAl6 Figure 2- l4 (Continued) pressed(pressingthe pushbutton providesa logic 0 to PINA.O). At this time, the program falls out of the ubile) Ioop and enablesthe \AIDT by setting WDTCR to 0x0b, setting Watchdog Enable bit high, and selectingthe timeout period. At this point, the \A{DT is activeand needsto be resetat leastevery 720 ms to avoid having it resetthe processor. As long asthe pushbuttonis held down, the programnow remainsin the secondzohile)loop. In this loop, the \AfDT is continuouslyresetby the assemblylanguageinstruction udr.-fhe \A{DT must be resetusing the embeddedassemblylanguageinstruction becausethere is no equivalentinstruction in C. The LED blinks continuouslywhile programis in this loop. When the userreleases the pushbutton,the programfalls out ofthe second rahile)Ioop and entersthe tuhik(l) loop, where it is held forever.Sincethe \AIDT is no longer being reset, approximately 130 ms after entering the whih(I), the \A4DT times out and resetsthe processor. This can be verified by noting that the processorresetsand restartsthe boodoader or by noting that the program is now back in the first tuhile) loop waäng for the switch to Depresseo. In order to prevent the program from accidentallydisablingthe \Ä{Dl it takesa two-step processto disable the \AIDT once it is enabled.Specifica1ly, the \4{DTCR must be first loadedwith 0x18 (setting the both \AIDE and \A{DTOE bits high sirnultaneously).Then Thc Itnel RISC Pra.ettaß the \\rDE bit must be deared as the ncxt instruction. Arr exanple is shown belorv: IIDTCR = 0x18; lrDTcR = 0c00; /;set IJDE and itDTOE sinultaneousLy*/ /1set ttDE Lo 0 innediarely*/ Normally the watchdog timer, once enabled, is never disabled becausethe purpose of enablingir ro .rar wirh is ro pfo(eclI he prores$ragäinslerranto' r'raric proce".rg. PARALLEL 2.6 I'O PORTS The parallcl I/O ports are the most gencral-purpose VO devices.Each of the parallel I/O ports has three associatedvo rcgsteß. the data dnernon regnftr,DDk\ (where "x'is A, B, C, and so on depending on the specfic processor arrd parallel port being used), thepori drtuer register,qpic ly called PORTx, and the parr pins regbtr,PlNx. Thc data direction register'spurpose is to determine which bits ofthe port are used för input and which bits are used for output. The input and ougut bits can be mixed as desired by the programmer A processorreset clcars all ofthe data direction rcgister bits to logic 0, setti ng all ofthe port's bits for input. Scfting any bit ofthe data direction register to a logic 1 sets the conesponaLngport bit for output mode. For instance, setting the least significant two bits of DDRA to a logic 1 and the other bits to a logic 0 sets the least significant two bits of port A for output and the balanceof the bits for input. Writing to the output bits ofport A is accomplished as follows: PORTA = 0x2; /*sers /*and Ehe seconal bit the othei clear of porl A*/ seven biEsr/ Reading from the input bits ofpon A is accomplished as follows: x = PrNA; /rreads all 8 pins of port a]/ In this laner enmple, "x" rvould contain the ralue from all ofthe bits ofport A, both inPut and output, becausethe PIN register refects the valuc of all ofthe bits of the port. Input port pins are floating, that is, there is not necessaily a pull up resistor associatedwith the port pin. The processorcan supply the pull up resistor,ifdesired, by writing a logic I ro the corresponding bit ofthe port driver registcr as shown below: DDRÄ = OXCO; PoRTA = Oxf; /*upper /*enable lower 6 as 2 bibs as outpui, pu1l ups on lodesr incernal inputa/ 2 bir:s*/ In general, although this raries by the specific processor,the port Pins are capable of sint<ing 20 mA, but they can source much less current. This means that the ports can dircctly drive LEDs, provided that thc port pin is sinldng the curent as shown in Figure 2 10. Figue 2-15 shows a program that usesthe least significant four bits of port C as inPut and the most significant four bits as ougut. Pull up resiston are enabled on thc input pins of the least signiicant two bits ofthe port. Additional information and eramples relative to the yO ports are shown in Section 1.5, "I/O Operations," in Chapter 1, "Embedded C Language Tutorial." t05 t06 *include void <nega16.h> nain (void) DDRC = 0xf0; PoRTc = 0x03; upper 4 bits /tseE putl-ups /tenable o f P O R T C */ /*bit6 of PoRTc as outpula/ on the 2 least slsnificantr/ while (1) P O R T C= { P I N C < < 4 ) ; /*read /*shift /*then the tower 4 biEs of POTRC*/ then 4 bits left and output*/ to the upper 4 bits of PORTC*/ ) ] Figure 2- fS Parc el Pott Exarnple Chapter 2 Example Proiect: Part B This is the second part of the Chapter 2 er<ampleprogram to deate a s'ßtem to collect op erational data for a stock car racer-ln the fust part, it was determined that the system has suffrcient memory resourcesto do the taslc In this part, the overall code structure and user interface will be created. It is impo.trnt to determine which peripheral resourcesare to be used for each measurement, input, and output. Ifyou were creati:rg the data collection qntem from scratch, you could determine the resourcesto use, ln4 as you assignedthe resou-rces, you would be sure that the processor had suflicient resources-In this case,however, you oeed to derermne which peripherals are being used for each measurement so you can write your program accordingly. Investigation, and perhaps a little circuit tracing, has shou'n that the system connections are as follows: . The Startbuttonis connected to the lNTl pin on the f4€ga163.Pressing it pulls lNTl low. . The Uploadbudonis connected to PonAbit 0-P.essing it pullsthe bit low. . The engin€rpm pulsesare connectedto the ICP (input capturepin). . The drive shaft rpm pulsesare connect€dto the lNTo pin. . The enginet€mperaturesignalis connectedto theADC3 (analog-to-digitalconvener input#3) pin. The Atnel RISC Prote$.rt For now, all that you need to be concerned with are the Start and Upload buttons. The other signalswill be handled in Part C ofthe example projectYou will now want to plan the overall structure of the program. Thinking back to Sec tion 1.12, "Real-Tim€ Methods," in Chapter 1, it would make senseto apply those meth ods to this project. In generrl, this progräm is supposedto record data at specific intervals and eventually upload the data to a PC for analysis.Using real-time programming methods allows us to keep the measurementsrunning in real time (using inteffnpts) and then to simply record the cunent values when the one-second interv'rl has elapsed.In other words, the measurementsare kept as current as possible all the time, whether they are being recorded or not. When the time comes to record the data, the recordrng function simply grabs the latest data and records it. So you will eventually need intemrpt service routines for the two rpm measurementsand the one temp€rature measurement. Addrtionälly, you must handle the Start and Upload buftons. A simple way to handle the job is for the program to record 120 sets of data and then stop; pressingth€ Strrt buttor simply dears the data set munter so it then records an other 120 sets of data at the time you want. The advantagehere is that pressing the Start bufton will ah€ys start a new set ofdata ir the casewhere sorneonesta-rtedthe recording processenantly. The Upload button would send the data whenever it is pressedif the 120 setswere complete. The following program skeleton seemsto 6t the needsand will be 6lled in as the Chaptcr 2 crample proceeds: +include Xi n c l u d e <nesa16.h> <stdio.h> 'sröo r'9r60 unsiqned unsigned unsigned aä/ oa a s6L cn-rj /"n-mber oi d.ra s-f, r.(o!ded' i1 F rpmrl20r, s rpmll20J; /{dlLoy- !o! Iz0 ce s o_ d-.char tenp[120] ; int currenL e rpm, currenL s rpm; current vaLues*/ /'nost char current tenp; '.e,.upr in!errup! /*pLace [EXT_INT0l code here to 0 sc !i.c rour irP./ void ext_int0_isr(voial) handle drive shaft RPM measurenent*/ 1 service rouhine*/ void ext inhl isr(void) /tclear counter to start I ' - -c 0 o.e-r'o, inLe--upL sprvi.4 ioufinar/ counting*/ lA7 t08 interiupt { /* place ITIMo ovF] code here to woid tinero_owf isr (woid) Proaluce 1 seco4d interwatsi/ < a2O) /* coale Eo reco.d a ser of data less /rif ttlan 120 sets are done*/ r/ ) /* Tine! inteirupt I /* Ptace 1 input caplure inter.upr serwice routi.e*/ ITIM1 CAPTI void rinerl-capr isr(woid) code here ro handle engine RpM neasurenenr*/ ) +define ADc vREF_TypE 0x00 /* ADC interrupt service rourine*/ interrupt IADc_INTI voial adc-isr (void) I /* Place code here to measure enqine renperaEure*/ void main {vold) I /* Input /output DDRC=0x00, PORTD=0x4C; DDRD=OXOO; porrs inlrializarion*/ /*enable pu1l up on bit /*enable pult ups on poli /* /* Tine!/counrer Iniriatizarion 0 inicializaEion*/ Eo be aalded late.*/ /' /* Triner/Counter Initialization 1 iniEializatioai/ to be addeal laEer'/ 0 for upload D, Bits swirch*/ 2,3, & 6*/ (s) inicializaEion*/ /* External hEelrupt GICR=0xc0, /* both externat iatserrupts enabled*/ MCUCR=0x0,A, /* set boEh for fallinq ealse triggered*/ /'.lpdr McUCSR=0x00, the inrerruoL !_ägs in case l-py "'e. G I F R =O X CO , ' /* erantty set*/ /x Tlner (s ) /counrer (6) rnretupE(s) TIMSK=oX21; /* tiner inre.rupEs /' UART inirializaLion* / /*ini!ializatioa to te adaledlarer^/ initializarionl/ enableal for larer user/ Th. l!n.l /* Analoer conparator disabled as it is RISC Pt at.t)aß not used*/ SFIOR=0x00; /* ADC initial i zation* / to be added laLer*/ /* ADc inirialization /* c1obal enable interruptsr/ { if :P \A.0) sFnd ddrd(); /'sand därd ro P. :- sr:r h p!. ..d' This code structure sets up the opeßtion of the entire system- INT1 is connected to the Start button; when the button is pressed,it resetsthe data set counter to 0. Timer 0 will be set (details to fo11owin the next part of the example) to produce an interrupt that will pro vide a one-second interval. Within the Timer 0 intemrot service rcutine. the data is recorded at a one-second interval whener.erttre data counteiis less than r20. So the scherre is as follows: pressing the Start button sets the data counter to 0, and data is then recorded until 120 sets have been recorded. In the meantime, all of the data is kept up to date in a real-time fashion by the various interupts. The last piece, uploading to the PC, is handled in the while(1) Ioop it nain).When the Upload button is pressed,the data is sent out seriallv. After turther sections of this chapter, more pieces of the exampte program will be added. 2,7 TTMER/COUNTERS Timer/counters are probably the most commonly used complex peripherals in a mic(ocontroller. They are highly versatile, being able to measure time periods, to determine pulse width, to measure speed, to measure frequency, or to provide output signals. Examplc applications might include measuring the rpm ofa car's engine, timing an exact period of time, such as that necessar,vto time the speedofa bullet, producing tones to createmusic or to drive the spark ignition systen ofa car, or providing a pulse-width or variable lrequency drive to control a motor's speed. In this section timer/counters will be discussedin the generic sense, and then g?ical timer/counters in the AVR microcontrollers will be discussedAlthough used in two distincdy ditrerent nodes, timing and counting, timertountcrs afe simply binary up counters. \[rhen used in timing mode, the binary countcrs are counting tirne periods applied to their input, and in counter mode, they are counting the events or pulses or something of this nature. For instance, if the binary counters had l-millisecond pulsesastheir itrput, a time period could be measuredby staning the counter at the beginning t09 I0 of an event and stopping the counter at th€ end of tÄe event The ending count in the counter would be the number of miliseconds that had elapsedduring the event. When a timer/counter is used as a counter, th€ eventsto be counted are applied to the input of the binary counter, and the number of events occürring are counted. For instance, the counter could be used to count the number ofcans ofpex coming down an assemblyline by app\ing one pute to the input ofthe counter for each can ofpeas. At any time, the counter could be read to determine how many cans ofpeas had gone dorvn an assemblyline. The A\ß. microcontrollen provide both 8-bit and 16 bit timer/counters. In either case,an important issue for the program is to know when the counter reachesits mllximum count and.ralh aeer.In the caseof ar 8-bit counter, this occun when the count reaches255, in which case the next pulse will causetlle counter to roll over to 0. In the caseof a 16-bit countcr, the same thing occurs at 65,535.The rcloru events are extremely important lor the progrnm to be able to accurately read the results ftom a timer/counter In fact, rollovers are so important that an interrupt is provided that will occur when a timer/counter rolls Some A\fR microcontrollers have two 8-bit timers (typically, Timer 0 and Timer 2) and one 16-bit timer (tpically, Timer 1), although this configuration will vary depending on the exact type ofAVR microcontroller being used.The following sections will discussthe timer prescaler and input selector,a feature common to all of the timers, and then discuss each ofthe common timers in turn- The most common usesfor each timer/counter will be discussed,although many timers have more functions than are discussedin this tc'<t. For any specific processor, check the specifications to determine all of the various functions possible with the timer/counten. 2.7.I TI].IER/COUNTERPRESCALERSANDINPUT SELECTORS Timer/counter units may use a vaiety ofinternal frequenciesderived fron the system clock as their input, or they may get their input ftom an extemal pin- The timer conntet eontrol .cg,ltd,. (TCCR, associatedwith thc timet corrta,trrsrhe rounter selsczbits (CSl, CSx1, CSx0) that control which input is used with a speciEc counter. Figure 2 16 shows the prescaler and input selector configuration for a timer munter control rcgister as used rn most A\aR micf oconüollers. The following code fragment shows,as an exarnple,how to initialize Timer 0 to use the s1stem clock divided by 8 as its clock source (the counter selectbits are tie three least signifi- cantbits ofTCCR0): TCCRO = 0x2; /*Tiner 0 uses clock/A'/ 2.7.2 TTMER0 Timer 0 is gpically an 8 bit timer, but this vades by specific processorgpe. It is capable of the usual timer/count€r functions but is most often used to create a time baseor ,d for the prcgtam. Timer eunter nntrol regitter 0, TCCRO, controls the function of Timer 0 by Tne /ltnel RISC Praceßars T,ner 0 ,rput Source! .- Time,/Count€r 0 Inpur S]6tem Clock (CK) \ cK/8 --------------{ cw64 -------------1a cw256 ------------a cw7024 a \ Switchpositioncontroled ExternalPinT0 l \, coxntn Ek.t bils Figure 2-|6 Tiner 0 PrcscoleSelectol selecting the clock source applied to Timer 0. Figure 2-17 shows the dock prescaler bit defrnitions for TCCR0. Other bits ofTCCR0 control additional tunctions ofTimer 0 u a manner similar to the control bits forTimer 1 presented later. Bit 7 Bit6 < Bn4 Bir5 Bit 3 Bir2 Bit 1 Bito cs02 cs01 cs00 Othcrbiß cs02 cso, 0 c500 0 Smp,Timu 0 is stopped SFtem Cloclg CK 0 0 0 SystemClock / 8, CK/8 Slsten Clock / 6d CKl64 0 0 S)ßten Clck / 256, CK/256 S]ßtm Clock / 1024,CK,/1024 0 Eftm,t Pin T0, comts a faling edge Ext@ar Pin m, couts a risi.g cdg€ Figure 2- l7 TCCRoPrcscalet Defnitktß l |2 A program ti.ck,like the tick of a clock, provides a highly accuratetiming event. The overall schemeis that a number is selectedand loadedinto the timer. The timer counts from this number up to 255 and rolls over.Whenever it rolls over, it createsan interruPt. The interrupt service routine reloads the same number into the timer, executesany time-critical activities that may be required, and then returns to the program. The cycle then repeats,with the counter counting up from the number that was loaded to 255, and rolls over, creating anotherinterrupt.The interrupt, then, is occurringon a regularbasiswhen eachtime period has elapsed.The number loadedinto the counter determinesthe length of the period. The lower the number, the longer it will take the timer to reach to 255 and ro11over, and the longer the period ofthe tick will be. As an example,assumethat a program is to toggle the stateofan LED every 0.5 seconds. The LED is attachedto the leastsignificantbit ofport C asshown in Figure 2-18. For a timer to be used as a ticlq the first necessarytask is to determinethe number that is loadedinto the timer eachtime the inteffupt occurs.In this example,we want the LED to toggle every 0.5 seconds.One obvious solution would be for the interrupt to occur every RESEI VCC AVCC AREF XTALI ADCT/PA7 AOC6/PA6 ADCS/PA5 AOC4iPA4 ADC3/PA3 ADC2IPA2 ADCI/PA1 ADCC'PAO SCKPBT M|SO/PB6 MOS|/PB5 ssiP84 oco/AlN1/PB3 INTZAINCVPB2 T1lPB1 XCK/'IO/PBO OC2IPDT lcPl/PD6 ocl A/PD5 OC1B/PD4 INTI/PD3 INTCVPD2 ]xD/Po1 XTAL2 AGND GND Hordwore Figure 2-f 8 LEDToggle RXD/PDO TOSC2/PC7 TOSCtPC6 TD/rc5 TOO/rc4 TMS/rc3 TCKPC2 SDA/PC1 scuPc0 T h . A t n e l R I S CP n . ü s a r : 0.5 seconds.In the caseofTimer 0, the slowestsetting of the clock prescaleris systen dock/1024. 6 MHzJ1024 = 5.859 kl1z, which has a period of 7/5.859 kllz = 171 ps This shows that every 171 microseconds another clock pulse will be applied to Timer 0. Timer 0 is an 8-bit tirner/counter, and so it can count up to 256 such periods before it rolls over So the total time that is possible rvith this hardware is as follows: 256' 771 ps = 43.69ms Forty-four milliseconds is not sufficient to time 500 millisecond events.In order to accomplish longer periods, a global countervariable is plac€d in the interrupt serviceroutine ofthc tick. So, for instance, ifthe tick occurs evcry 50 milliseconds, in this examplewe would want the countcr to count up to 10 bcfore toggling the LED (10 " 50 ms = 500 ms). The choice ofa reload number is up to the programmer Usually, it is desirable that the reload number produce an even and easy-to-use time delay period, such as 1 millisecond or 10 milliseconds. In the caseofthe 6 MHz do& shown in the example,using the divide-byeight prescalerwiJl give a clock period of 1-33 microsecondsfor each clock pulse applied to the counter Given a 1.33-rnicrosecond clock applied to an 8-bit counter, the mlximum time possible using the counter alone would be as follows: 1.33 us '256 counts= 340 us 340 microseconds is not a verv even period of time to work with, but using 225 counts would give a timeout period of 300 microseconds. Therefore,the counter reload number would be as follows: 256-225=31 Rollover occus at count numbcr 256, and it is dcsirablc for thc courtcr to count 225 coun$ beforc it rolls over: therefore. the reload number in this caseis 31. This means that the ir terupt senice routine will be executedonce er"ery300 microseconds (1.33 ps/clock cycle 225 clock cycles/interupt clde = 300 Fs/intenupt clde). A global variable will be used to count to 1666 to produce the entire 500 milliseconds time period (300 gs - 1666 = 500 mt. The en üe progrm is showr in Figure 2- 19. Figure219illustratesalloftheconceptsdiscusscdabovc.Thetimcr/counterregisteritself, timer caunter0 (TCCN-f 0), is reloadedwith the value 31 each time the ISR cxccutcs so that it can once again count up 225 stepsto reach 255 and roll over. A global variable called 'tinecount" is used to keep track ofthe number of times that the interrupt senice routine is executed by incrementing it each time the ISR is e.recuted. "tinecount" is both incrementedand checkedinside the expressionofthe ifstatement. When "t imec ount" rcaches1666, the most signifcant bit ofport A is toggled, and " t ime count" is reset to zero to count up for the next S0O-millisecond period. This tick could also handle any other event tlnt occurs on an even number of300 microsecond increments in 3 4 +inctude <mega16-h> staEic unsiqned int tine-count; /*-5 secoEd counrer*/ // Tiner 0 overflow interrupt service routiEe interrupl ovf isr(woid) ITIMo ovF] woid tinelo t TCNTo = 31; /*set for 300 us Eineout*/ ++tine_count; /*increnent .5 second counter*/ if (tine_counE == 1666) { PORTC.0 = (PoRTC.0 ^ 1); /*co(plenenE porr bi! Eine count = 0; tine counler for nexr /t.eset ro blink r,ED*/ .5 second*/ ) void nain (void) DDRC = 0x01; /'ser 1sb 'ser Limer 0 prescdler TCCR0=0x02; T C N T 0 = 0 x 00 ; /* unnask Time! TIMSK=0x01; for to outpuE*/ cLk/8// 0 owerflos inEerrupt*/ { i /*do loLhing in here r/ ) ) FiSure 2-f9 LEDBlinketPrcCrcn 2.7.3 TTMERI The 16-bit timer (Timer 1 &om an ATMegal6 is used as an erample) is a much more versatile and complex penpheral than the qpical 8-bit timers. In addirion to the usual timer/counter,Timer 1 contails one 16 bit input capnue registerand two 16-bit output compare rcgisters.The input captre register is used for measuring puJsewidths or captudng times. The output compare registers are used for producing frequenciesor pulses from the time/counter to an ouq)ut pin on the microcontroller. Each ofthese modeswill be discussed in the sectionsthat follow. Remember, howeveqthat atfhoügh each mode is discussedseparately, the modesmay be, and often are, mixed together in a program. The lt"'el RISC Proce\!ars Timer 1 is also conceptualy very different from Timer 0. Timer 0 is usually stopped, started, reset, and so on in its normal use. Timer 1, on the other hand, is usually left running. This creates some considerable differences in its use. These differences will be discussedin detail in the sections that follow, co\,ering the special usesof Timer 1. Timer 1 Prescaler and Selector In spite of its many special features,Timer 1 is still a binary up-counter whose count speed or timing intervals depend on the clock signal applicd to its input, just xs Timer 0 was. As with all peripherals in the microcontroller,Timer 1 is controlled through a control register T;ner/caanter cantnl reg;ster7, TCCR1 (the AIMegal6 tirner control register for Timer 1), is actually composedoftwo registen, TCCR1A arrdTCCRIB. TCCR1A controls the com pare modes and the pulse width modulation modes ofTirner 1. These will be discussedlater in the section.TCCR1B controls the prescalerand input multiplerer for Timer 1, aswell as the input capture modes. Figure 2-20 shows the bit definition for the bits ofTCCRlB. tsir 7 ]CNCI tsir6 Bit t ]CEST Bit 4 Bit 3 Bn2 tsit1 Bit0 WGIVI 13 WGM 72 cs12 c51l cs10 8it ICNCl ICESl Input Captur Noüe Ceceld (1 = enabled) Intut CaptureEdge Selet (1 = rising edse,0 = faling edgr) WGM 1x Ouqut *arcfom cs12 mntrcl. SeeTCCR1,{ CounterInput Seled Birs Encdv the sme detuition asfor Timer 0 CS11 CSlO Figure 2-20 TCCRIE Bh Defrnitions "lCCRlB eoanterselettbrrscontrol the input to Timer 1 in exacdy the same manner ff the counter selectbits of Timer 0. In fact, the three selectbits provide clock signals that are absolutely identical to those ofTimer 0. Timer 1 Input Capture Mode Measuring a time period with Timer 0 involves strrting the timer at the beginning of the event, stopping the timer at the end of the event, arld linally reading the time of the event fiom the timer counter rcgister The särnejob with Timer 1 is handled diff'erently because Timer 1 is always running. To measurean event, the time on Timer 1 is captured or held at 5 |6 the beginning ofthe event, the time is ,lso captured at the end ofthe event, and the two are subtracted to 6nd the time that it took for the evcnt to occur.You would do nuch the sarr ifyou are t5'ing to frnd out how long it took you walk fiom your history classto the bookstore.You would note the time when you left history dass, again note the time when you arrived at the bookstore, and subüact the two times to determine how long it took you get to the bookstore. In Timer 1, these tasks are managed by rhe ;n?xt ta?türe reg;ster(1CR1). ICR1 is a 16 bit r%ister (made up ofICRlH and ICRIL) that will capture the actual reading of Timer 1 when the nicrocontroller receivesa certain signal. The signal that causesa capture to occur can be either a rising or a falling edge awlied to the in?ut capture?in, lCP, ofthc microcontroller. As sho\.tnin Figure 2-20, the choice ofa rising or falling edge trigger for the capture is controlled by t]\e ;npt captureedge.r/a'l /4 ICES1. Setting ICES1 will allow ICR1 to capture the Timer 1 time on a rising edge,and dearing it wil allow ICR1 to capture the tirne on a falling edge. As is probably obvious by noq since there is only one capture register ardlable to Timer 1, the captur€d contents must be read out as soon as they are captured to prev€nt the next capture from overwriting and destroying the prcvious reading- In order to accomplish this, an interrupt is provided that occun whenever new data is captured into ICR1. Each time the capture interrupt occus, the prcgram must determine whether the interrupt signals the be ginning or the ending of an event that is being timed so thar it can treat the data in ICR1 aPpropriately. Timer 1 also provides an input noise canceller feature to prevent miscellaneousunwanted spikes in the signal applied to the ICP ftom causirg a capture to occuJ at the wrong time . When the noise canceller featur€ is active, the ICP must remain at th€ active level (high for a rising edge,or low for a faling edge) for four successivesamplesbefore the microconuolier will treat the trigger as legitimate and capture the data- This prevents a noise spike from triggering the capture register. Sernry the ;x?at ca?ture noise cancelhr /ia ICNC1, in TCCR1B enablesthe noise canceler feature (rcf€r to Figure 2 20). The hardware and software shown in Figures 2-21 arrd 2-22, respecrively,demonstrate the use of the input capture register.The goal of this hardware and software is to measuretlle period ofa squan wave appli€d to the ICP of the microcontroller and to output the result, in milliseconds,on port C. The software in Figure 2-22 has sweral featuresworth noting. A #defne statement is used to connect a meaningful name with the output port. The ISR for the Timer 1 overflow does nothins more than increment an overflow counrer when the overllow occurs during a period measurement.The numb€r ofoverflows is used in the calculation for the period. The In?ut Ca?tureh)ent ISR occurs evcry time the input waveforrn is a dsing edge.At this instant, the ISR readsthe input capture register to get the time that was captured when the The Atnel RESET VCC ADCTtPAT ADC6/PA6 ADC'PAs ADC4|PA4 ADC3/PA3 AOCUPA2 ADCI/PAI ADCIVPAO RISC Processort Pulseinput,TTL level SCKPBT M|SO/PB6 MOSUPBS ss/PB4 oco/atN1/PB3 INT2/AINO/PB2 T1lPB1 XCK/TO/PBO AVCC AREF (t2lPD7 tcPl/PD6 oclrPos OCJB/PD4 tNTl/P03 tNTC|/P02 TXC'P0l RXD/POO XIALI XTAL2 AGNO GND 10sc2JPC1 TOSC1/PC6 TDUPC5 lDO/rc4 TMS/rc3 rcwPc2 SONrc1 SCUrcO MEGAI6 Figure 2-2 | PeriodMeosurement Hordwore <mega16 . h> +include /*define froerane Port C as peraoo_ouE unsigned unsigned char ov_counl:er; int starting_edge, ihr "hci^.aÄ /+rnimor for output PoRlu 1 pulse for /*counter ending_edge; ^l^^Lc. ^!rarFl^L, width*/ F^r.^f,,.1 1 overflow*/ timer for times*/ /'storage -l^^L ^^!!nrc ih r}!Ä TcD*/ I ++ov_counEe-r; /*Timer 1 input intarrrrht l'r'TM1 /*incremenc capture cAp'r'1 councer when overflow ISR*/ ltî.l rimayl .^^l i<.1\/îd) { Figure 2-22 PeriodMeosurement Softvtore(Continues) occurs*/ ^"1cö*/ |7 lt8 rhe two I biE capruie /*combine legisLers idto the 16-bit countr/ ' ICRIL; /'get anoinS eogand fime ro- p6r'oo 256.l.RlH = {unsiqned clocks tons) endinq,edqe * 65536) + ((ünsigned loDs)oLcouoter (unsiqneal long) startinq_ealqe; period out = -(clocks / ?50); /*ou!put nllliseconds ro Polr c*: overflow counter for this neasurenenti/ /*crear = 0; ov_counter /*sawe end tine to use as slarting ealge*/ starting edse = endinqr_edse; ] nain (void) void I DDRC=oXFF; Polt c for outputt/ /*set TCCR1A = 0; alt wavefom functionsr/ /idisable TccRlB = 0xC2;/aTine! 1 input to clock/8, enabte input capturea/ TIMSK = 0x24; /rumask Einer 1 overflow and capture interrupts*1 +-smr'_ei while ) /'enablF qlobdl inter rupL bit'/ (1) { ; /'do oolhiner here*/ ) l Fiaurc 2-22 PeüodMeosuEnentsofblore (Contnved) rising edge occured. This number is the actual count of dock ticks that was present when the input capture event occurred. BecauseICR1 is composed oftwo separate8-bit registers (ICR1H and ICRIL), they must be combined into an integer sized number to use in the period calculation. This is accom plishedby: ending edgö - 2c6'rcPlH I tCPlr; /'qör ano rjm- ro- p-r oo Multiplying the 8-bit result is exacdy the same as shifting the number form ICR1H eight bits to the l€ft, making the more significant bne ofthe integer count. The result ofthis multipl ication is added to the value ftom ICR1L to form the complete integer result. This num ber is the timer count at the azzlof the period being timed. The count from the start ofthe period is the same as the ending count from the previous period. The total number ofclock ticls that occurred during the measurement period may then be calculated as follows: clocks = (unsisDed long) ending edge ] 65536) + ((unstqned long) ov counter - (unsiqrned long) sharting ealge; The lthe/ RISC Ptut,!sat The second line ofthe equation accounts for arry overflows that occurred during the meaThe timer is being clocked by Fclk/8 (6 MHz / 8 = 750 kllz), which means that lor every millisecond that has elapsed,750 counts have occurred. Finally, dividing the total number ofcounts by 750 producesthe actualnumber ofmilliseconds in the measurementpedod. Timer 1 Output Compare Mode The output compare mode is used by the micmcontoller to produce output signals.The ouguts may be squareor asymmetrical war.es,and they may be varying in frequency or symmetry Ouput compare node, for instance, would be appropriate ifyou attempt to program a microcontroller to play your school's fght song. ln this case,the output compare mode would be used to generate the musical notes that make up the song. Out?ut comparc mode is sort of the antithesis of input capture mode. In input capture mode, an exernal signal causesthe cunent time in a timer to be captured or held in the input capture register In output compare mode, the prcgram loads an ,üt?ut ünPare re9^ lrr. The value in the output compare register is compared to tÄe r€lue in the timer/counter register, and an intefupt occurs when thc two values match. This interupt acts as an alrJm clock to causea processorto executca function relative to the signal it is producing, exacdy when it is needed. In addition to generating an interupt, output compare mode can automaticaly set, clear, or toggle a specilic output port pin- ForTimer 1, the output compare modes are controlled by timer eaanter cantral regito 1A, TCCRIA. Frgre 2-23 shows the bit definitions for TCCRI A thar relarero ourput compareoperatlon. Bn7 Bn6 Bi!5 Bir4 Bir.] COI,I1A1COMlAO COM181 COMlBO FOClA Bir2 FOClB Bit I Bir0 WGM11 WGMlO COM1Ao & CO]lIlAl Co'dol thc comparcmodc tundion for compc resisterA CONI1B0 & CONIlBl Contrcl the comparemodefi,nction for compüe resisterB contrcI Bit Deltnitiors COMI|I COMI\O Function. ('l it'A' or'g 6 aPprcttiote) 1 Compre mtch mggles the OClx line 0 No Output 1 1 Figure 2-23 Compre match cleß the OClx line to 0 I Comp@ match sets the OClx line to 1 TCCRIA Bit Definitjotßfot OutputConporcMode 9 t20 As shown in Figue 2-23, compare mode control bits determirc what action will be taken when a match occurs between the comparc register and the timer register. The associated ouQut pin can be unaffected, toggled, set, or cleared-The match also causesan intetrupt to occur The goal of the interrupt service rcutine is to reset or reload the compare register for the nerr match that must occui By way of example, assumethe microcontroller needs to produce a 7.5 kHz squrre wave. This schemeworks something like this: | . Whenthe first matchoccurs,the outpurbit is toSgled, ändthe interruptoccurs. 2- In the int€rruprserviceroutine,the progmmwill calcolate whenthe next match shouldoccurandloadthat numb€rinto the compareregiste'iIn this€ase,the7.5kHz wävefrcrm ha5a periodof 133.3microseconds with 0.667microseconds in eachhalfof the waveform.Sorie time from one toggleto the next is 0.667microseconds.Using the frequency of the €lockappli€dto the timerithe p.ogramcalculates the numberof clockt'cksrharwilloccurin 0.667microseconds. 3. Thisnumberof clocktick is äddedto the existingcontentsof the compareregister and reloadedinto the compar€reSisterto cäusethe next toggleandto repeatthe calculationandreload€ycle. An exampleofhardware and sofrwaredemonstrating theseconceptsis sho*'n in FiguJes2 24 and 2-25, respectively Note that no ertemal hardlvare is requied becausethe signal is produced entirely by the microcontroller In the program in Figure 2-25, notice first the initializations that occur in na;n0. Register DDRD is set to üx20 so that the output compare bit, OC1A, that relatesto output compare register A, OCR1A, is set for output mode, so that the output signäl can appear on the bi!. TCCR1A and TCCR1B set the prescalerto clock /8 (in this casectock = 6 MHz, so clock /8 = 750 kHz) and set the output compare mode for output conpare register A to toggle the output bit, OC1A" when a match occun. And finally, the compare interupt is unmasked by setting the OCIE1A bitin the t;mer intenu?t maskrcg;ne\TlMsK. Information such asthat shown in Figure 2-26 is used to calculate the number that is added to the compare r€ister contents to determine the point ofthe n€).1toggle. In this case,onehalf of the waveform is 66.7 microsecords long. Since the clock applied to the counter is 750 kHz (dock/8), the number of clock cycles between match points (waveform toggle points) is given by the following length of time between toggle points/clock cycle time = interval number or, for this example, 66.7 ;rs/1.33 ps per clocL cyde = 50 dock c1'clesper match point And so, for this arample, each time the compare match intermpt occurs,50 is added to the cunent contents ofthe comp?re register to determine when the next match and toggle of the output waveform will occur Tbe Atmet RISC Protessors RESET V@ AVCC AREF xrALl XTAL2 AGNO GNO Figure 2-24 ADCT/PA7 AO@/PA6 AOC5/PA5 Aü:4tPA4 AOC3/PA3 ADc21PA2 ADCI/PA1 ADCryFAO SCKPBT M|SoiPBo MOSt/P85 S9P94 oc(yatNl/PB3 INI2/AINOFB2 T1IPBI XCK/TO/PBO ac2tPaT ]CP'PD6 oc1&PD6 ocls/PD4 INTI/PDO NTO/P02 TXD/PO1 RXD/PM 7.5kHzoutput TOSCzPCT loscl/P@ TDI/PCs TDO,FC4 IMS/PC3 tcKtPc2 SONrc1 scuPc0 7.5 kHz Hordwore One additional important point to consider relative to the output compare registers, and specifically relative to the calculation of the next match point number, is the situation in which adding the interv-al number to the curent contents of the compare register results in a number bigger than 16 bits. For example,if the output compareregistercontainsa number 65,000,and the interval is 1000,then 65,000 + 1000 = 66000 (a number greaterthan 65,535) As long asunsignedintegersare usedfor this calculation,thosebits greaterthan 16 will be truncated and so the actual result will be 65,000 + 1000 = 464 (drop the 17th bit from 66000 to get 464) This will work out perfecdy, since the zut?ut comParereghter is a 16-bit register and the timer/counter is a 16-bit device as we11.The timer/counter will count from 65,000 up to 65,536 (a total of 536 counts) and then an addttional 464 counts to reach the match point. The 536 counts plus the 464 counts is exacdy 1000 counts,as desired.In other words, in both the timer/counter and the compare register, rollover occurs at the same point, and as long as unsigned integers are used for the related math, rollover is not a problem. l2l tzz + inctude 'Ti ' e <nega16.h> e' r oulpuc compdrF A inla|upL service rouFine' uo. IrIMt COMPAI void l imar l_compd_isr (voicl) { is rea11y OCR1AH and ocRlAL but CVAVR providesr /*oclÄ 'a o-uedo 'eqiste! OCRIA thor is lhe inlese' resurt conbininq /*of the lwo I bit registers*/ 0cR1A = ocRlA + 50; poinr}/ /*se! tso nexc naLch {roggle) void nain (void) { DDRD=0x20; /*set OC1A bit TCCRlA=0x40; / tseE prescaler conpare noile compare natch foi output*/ to to clock/8rl Eoqqle oclA interrupt for pin on natch*/ TCCR1B=0x02; /*unnask outsput TIMSK=0x10; / tset vhile t q1oba1 inre.lupt reqisler bitl/ (1) ] Figure 2-2s 7.5kHz Softwore <- 133.3gs '< Figurc 2-26 7.s kHzwovefom 66.7Vs --------- a*/ T b e4 t n e t R I S CP n r ü ' a t ' Timer 1 Pulse Width Modulator Mode Pulsetridtb nadalation (PWM) mode is one ofa number of methods of providing digitalto analog conversion. P!14\4 is the schemein which the duty cyde of a squarcwave output fiom the microcontroller is raried to provide a varying DC output by frltering the actual output waveform to get the ar.erageDC. Figure 2-27 illustrates this principle. As is shol'm in Figure 2 27, warying the duty cyr:le,or proportion of th€ cycle that is high, will vary the averageDC voltage of the wavdorm. The waveform is thefl filtered and used to control analog devices,creating a digital-to-analog converter (DAC)- Examples ofP\AM control schemesare shown in Figure 2-28. In Figure 2-284, the RC cncuit provides the filtering. The time constant of the RC circuit must be significandy longer than the period ofthe PWM wavdorm- Figure 2-288 shows an LED whose brighmess is controlled by the PWM waveform- Note that in this exampte, a logic 0 wi[ turn the LED on, and so the brightness will be inversdy proportionäl to the P\4M. In this case,our eyesprovide the fihering becausewe cannot distinguish ftequencies above about 42 Hz, which is sometimes called the flicker rate. In this case,the ftequency of the P\4M waveform must exceed42 Hz, or we will seethe LED blinl: The final arample, Figure 2-28C, sho*s DC motor control using PWM. The filtering in this cncuit is largely a combination of the mechanical inertia ofthe DC motor and the inductance of the windings. It sirnply cannot physically change speedfast enough to keep up --..-..-..-.-.-' -<-As. DC -<-Avg. DC Fisure 2-27 PWM Wovefoms 123 t24 PWMInput AverageDC output c B + MotorVolts DC Q1 PWM Input PWMInput Figure 2-28 PWM Exomples with the waveform. The capacitor also adds some additional filtering, and the diode is important to suppressvoltage spikescausedby switching the current on and off in the inductive motor. One method of creatingP\ÄM with Timer 1 would be to use the output compareregister and, each time a match occurs,vary the increment number being reloadedto üeate the P\AM waveform. However, Timer 1 provides a built-in method to provide P\ÄM without the need for the program to be constandy servicing the compare register to create a pulse width modulator. Timer 1 changes its mode of operation in order to provide P\AM. When operating in PWM mode, Timer 1 counts both up and down, making it difficult to use any of the other Timer 1 modes with P\MM mode. During PWM operations,Timer 1 counts from zero up to a tap value andback down again to zero. The top value is determined by the resolutiondesired. PWM is provided in 8-bit, 9-bit, or 10-bit resolution as determined by the Waveform Generation Mode (WGM) selex bits in TCCR1A (refer to Figure 2-23). Figure 2-29 shows the effect of these bits on P\AM. Figtre 2-29 shows that the resolution chosen wi.ll determine the top value for the counter to count up to and down from, and it will also affect thefreguencyofthe resulting P\AIM Tbe '1tfle/ RISC Prrtessars PWVIR€soru.ion wctIl1 wct410 0 0 0 I P$.1\4Disablcd I bir FiAure zJq 1 2ss(oxlf) 511 (0x1lI) 0 1 TimerT.öValue 10-bn 1023(oi3tr) Wovefon GenerutotModeSelectBits r.rveform. For example, choosing 9-bit resolution will result in a top count of511 and the P\\M ftequency as calculated below Given a 6 MHz system clock with a + 8 prescaler): fnun = fq*.-a-t /(prescaler * 2 * top count) = 6Mhz / (8" 2.511) = 733.aHz Resolution is the 6neness,or accuracy,ofPlVM control. In 8 bit mode, P\ÄM is controlled to 1 part in 256; in 9-bit mode,PWM is controlledto 1 part in 512; and in 10 bit mode, P\\M may be controlled to 1 part in 1024. In PVy'M, resolution must be weighed against frequency to determine the optimum choice as higher resolutions produce lower ftequency P\4M signals. The actual dury cycle being output in PIAM mode depends on the value loaded into the ougut comprre register for the timer/counter. In normal PJAM mode, as the counter counts down, it sets the output bit on a match to the output compare register, and as ir counts up, it clerrs the o\rtput bit on a match to thc output compare rcgister. In this man ner, loading the outp\rt compare register with th€ value equal to, say,20 percent of the top value will produce a 20 percent duty cycle waveform. It is also possible to provide the in verted P\\M for applications such as controlling the brightness ofan LED connected in a cuüent sink mode direcdy to the PIVM output pin-loading the output compare register to 75 pcrcent ofthe top value in the inverted mode will produce a 75 percent low duty cycle Figures 2-30 and 2-31 shorv the hardware and software, respectively,ofan cxample program using P\Ä/J\,I.This program providcs four ditrerent duty cycles (10, 20, 30, and 40 per cent at a frequency close to 2 kHz) basedon the logic levels applied to port A. Sening the exact frequency ouput requires juggling the timer prescaler and the resolution to get as close to the desired frequency as possible-The table in Figu-rc2 31 shows the frequency output (calculated using the formna presented previously) for all possible combinations of the prescalerand resolution, given the 8 MHz system clocL From the table, we can pick the combination that provides the frequenry closest to the one we desire. If the problem had requned a particulr resolution of the PWM, the choices from the table would be Iimited by the resolution, and the frequency might not have been as close. t25 t26 u$1 RESET 9 vcc AVCC AR:F XTAL1 Q1 XIAL2 cl 20 pfd 20 pfd -3c-----il z-- -iscKPgT MrSOlPg6 MOSt/P85 ss/Pgl o@/AtNl/PB3 IMTZAINCVPB2 T1/PS1 xc|(rc/Ps0 .01 ufd c2 aoc7tPAT AOC6/PAO ADC5/PA5 AOC4/PA4 ADC3/PA3 AOCZPTz AocltPAl AOCo/PAo AGND CND (EZP07 |cP1/PTA ocla/Po5 OCIB/PO4 lNTl/PO3 tN'0/P02 TXf,POl RXO/PDo OüSut to6c2rc7 TOSC1/PC6 TDUPC5 TDo/PC4 IMgPC3 lcK]PC2 SDA/PC1 SCUP@ MEGA16 Figure 2-30 PWM Hordwore For this e-rample,Figure 2-31 shows that 8-bit resolution and system clock/8 would give 1.96 kHz, which is very closeto the desiredfrequency.Figure 2-31 also demonstratesthat the frequency choices for any given combination ofcrystal, prescaler,and PWM resolution are fairly limited. If a project requires a very specific P\ÄIM frequency, the system clock crystal will likely have to be chosen to allow this frequency to be generated at the desired resolution. The program shown in Figure 2-32 usesa switch/case statement to select the duty cycle of the P\AM output. A #define statement is used to mask port A so that only the two lower bits are used as input, and port A is set to 0x3 so that the internal pull-ups are enabled on the samelower two bits. This avoids the need for external pull-up resistors. TCCR1A andTCCR1B are initialized to selectthe P\ÄM mode and the orescalerto orovide the desiredfrequencyoutput. Processortime in many microcontrollerapplicationsis precious.In this program,an ifstatement is used along with the variable "otd-sd' so that new data is written to the pulse width modulator only if the switches are actually changed, thereby preventing continuous writes to the output compare register. Tbe,4tn,1 RISC Proc4tott PWM Mode e-ah (op= I : u ä ( g-Bi. (T6p='tt) 255) srstemclock 616r = 15.7kHz fa*' = 7.8 kUz fFor = 3.91kHz slstemclock/ 8 f$vM = 1.96 kHz fp\lir = 978 Hz lavM = a89 Hz hw = 722}f2 fP\w = 61 Hz =245H2 fM SystemClock/ 64 S)ßtemCrock/ 2s6 fBr.Ir =61H2 fnll"l = 31Hz S]stcm Clock / 1024 fi6r = 15Hz fFF Figure 2J I #include fPlvni = 15 FIz =8Hz fA6r =,1H2 / (prcscalcr'2'top count fm.rr = &"-a* FrcquencySeledon Chottfot on a MHz Systen Cb.k <neqa16.h> '-sp d-f o sel lhc Lwo lowest * input. */ / control (PINA & 3) +define PitM select void l ILBit (Top= t023) oa po'. bi!s C r'e' "s nain (void) r s oned' PORTA = DDRD = TccRlA TccRlB if ! old sw: /tsr o!dge to! posf 0x03; /*enable the inEelDa1 pu1l 0x20; /*OC1A as outpult/ = 0x91;/*compare A for non inv. = 0x02; /*clock / a prescalert/ (Pm4 selecl vd.ua ups for PwM and ot in I inpuc' the biE inpul resolution*/ != o1d sw) t old Figure 2+2 sw = PwM select; case 0: case 1: /rsave OCR1A = 25; break; ocRlA - 51; break; (Contjnues) PWM Soft://orc /'!0 /*202 toggle S duEy aluty switch cycle cycle biEsl/ value*/ desiredt/ desired*/ 127 t28 case 2: '16i OCR1A = /*34$ aluty case 3: OCR1A = A02; /*4A$ duLY cyete cycle ilesired*/ alesired*/ ) , Figure 2-32 Pw Sofülorc(Continueq 2.7.4 TTMER2 Timer 2 is usually (depending on a specifrc microcontroller in use) an 8 bit timer/counter with output compar and PWM features similar to Timer 1. The most interesting difference with Timer 2 is that it can use a crystal separatefrom the slstem clock as its clock source. Selection of the extemal crystal as the clock source for Timer 2 is accomplished by setting the AS2 bit h dte arynthronourxatu /qg,rrer (ASSR). The bit definitions for the bits ofASSR are shown in Figure 2-33. Setting the AS2 bit allows Timer 2 to usethe extemal crystal as its clock source.This means that the clock sourcefor Timer 2 is running asynduonously to the microcontroller system clock. The other three bits in th€ ASSR rcgister are used by the programmer to ensurc that data is not written into the Timer 2 rcgisters at the samemoment that the hardware is updating the Timer 2 registers. This is necessarybecausethe oscillator ofTimer 2 is asynchronous to the slstem oscillator, and it is possible to corrupt the data in the Timer 2 registers by writing data to the registers as they attempt to update. A single control register,TCCR2, controls the operation ofTimer 2. The TCCR2 bit def initions are shom in Figure 2-34. Using, for instance, a 32.768 kHz crystal allows Tirner 2 to firnction as the time bäse for a real time clock. UsingTimer 2 in this vlzywill allow the microcontroller to keep accurate time when necessarySimply allowT2 to run with the 32-768 crystal and it will overflow exacdv 128 times each second. Br7 Bir6 Bit 5 Bir4 Bir 3 A52 Figure 2-'33 ASSRBit Deltniüons Bn2 Bit 1 Bir0 TCN2IJB OCR2UBTCR2LIB Tlt e.4 t n eI RI S C P ra A sar: Bir 7 Bir 6 Bit 4 FOC2 wctJ20 cot121 Bit 3 colu20 WGIVI2l Bit2 Bit t Bit 0 cs22 C521 CS2O air FOC2 WGM2O COrvI2t Force a Compm march i. no. PWNI mode- Settingthis bit dables the Tind 2 PIVM ftn tion. cotI20 Thesetvo bns set the outDut@nDd node ftnction. The bit definitions a( ,dcnd(rlto theCOMrxl dd COIUlxo b,t! of nner l WCM21 S* to enable ounter cler on compre match. cs22 cs21 Courter Dßc.ler selet bits for Timer 2. SeeAVR sDe..for details. CS2O Figure 2-34 TCCR2Bit Defnitjons Chapter 2 Example Proiec* Part C This is thc third part ofthe Chapter 2 example system to collect operational data for a stock car.This part will be concerned with using the timers to measurethe one second recordi"c interval and the two rpm measurements. ONE-SECOND RECORDING INTERVAL USINGTIHER O Using a timer to producc a "tick" or delay interv-al has been discussed.In this case,you are trying to produce a long (in rnicrocontroller terms) time inten'al, and you have severalother interupt dependent processesrunning aswell. So it would be well to use as dow a clock as practicd for the tick dock so as to ninirnize the amount of time used in the tick routine. Further investigation of the Mega16 system you have becn assignedto use shows that the systemclockis8MHz.TheTimer0prescalerallowsdivisionratiosof7,a,64,256,a. 1024. Choosing a prescalervalue of 64 produces a 125 kFIz clock applied to timer 0. Now you can ligure out the number ofclock pulses that must elapsefor 1 second to have passed.In this case it is easy,and 125,000 clock pulses must occur for 1 second to have elapsed.Timer 0 is an 8-bit counter and can only count up 255, so you selectto have it count 250 counts per tick. 125000 / 250 = 500, meaning that the timer interrupt must occur 500 times for 1 secondto haveelapsed. The foüowing code is plzced n na;nQ to rnneJuznT'tnelt: /* Tiner/counter 0 initialization* / TccR0=0x03; TCNT0=0x00; /*c1ock /*sLart set to tinero clk/64* / at 0 */ t29 130 The following code is placed rbo\te na;n0 ^s the interrupt service routine for the Timer 0 inr tine /* Tine! inEellupt cntr = 0; /*qloba1 variable interrupt 0 overflos ITIMo oVFl TCNTo = 6; (tine if cntr++ /iretoad == 500) for service nunber of Tiner 0*/ rou!ine*/ cinei 0 for next period*/ for one second, increnent /'check counter*/ { if (data set_cntr e lpmldata set < 120) cntrl /'record = currenE dara if e !pn' less Lhan 120 sets*/ engine /*record rpn*/ ) counter /*reset for next 1 second interval r/ Notice that the "aata set cntr" vriable is post-incrementedas a partofthe storing of ENGINERPMMEASUREMENT USINGTIHERI The input capture feature is used to capture the period ofthe engine rpm pulses.The period is used to calculate the rpm- Note that one pulse occun for every two engine revolutions rn a I cycle engine such as this oneThe systemclock is 8 MHz in this system,so using a prescalerof8 will providc clock pulses of 1 MHz with a convenient period of1 microsecond.These clock pulses drive Timer 1, and the i ? t ca?tareregbter flCR1) will be used to capture the Timer 1 count each time a falling edge occLrn on the ICP ofthe AIMega16. When this occurs, an interupt will be generated. In the intenupt service routine, the current captured count is compared to the previously captued time to determine the period ofthe pulscs,which is used to calculate the engmerPm. The following code is pbced n nain) 1o'ann:Ize Timer 1 to capture the time on the falling edge: / * T i m e r( s ) / c o u n t e . ( s ) I n t e r r u p ! ( s ) i n i t i a l i z a t i o n * / TIMSK=0x21; /* /* Tiner/Counter TCcRIB=0x02; TCNTlH=0x00; TCNTlL=0x00; tinero l ini overflow, t ial i zahion* /'prcscdler aE / *start ICP interruprs / 8, 0tl enabled*/ ^dpfuie on ra 19 -o96 Tb..4tnel RISC Prat.)!ore A,ndthe following code males up the ISR for the captureevent: unsiqned inE previous caprure tlne; /*saweal tifre fron previous*/ / * captDte* / /* Timer 1 inpui capture interrupt service .outine*/ inLerrupt I T T M 1 _ C A P T ]v o i a l E i n e r l c a p t i s r ( v o i d ) { .nsigneo 'r. cu 'Fi._cdplLre_Lime, pe'iod; /,cu!!enr /.Eerioa. tim- ano' / current_capture Eine = (256* ICRIH) + ICRIL; /*get captured tine*/ if (cu4ent_capture Eine > previous capture ti(e) /*check rollover*/ :ne; previous rapruroe od - cur 'e.t_cdolure Lime peiiod = oXFFFF - current_capture tine + previous capture = (unsiqneal lonq)120E6 / (unsiqned long)period; cudent_e_rpn p)aviols .äplu-6 I ime .LIenL_cdpLuie_time; tine; /'save to! nex.' / *calculationt / ) In this code, a global r,ariable, "previous caprure Eime", is initialized to retain the value from the previous capture. The ISR function reads the curent capture time and uses it, aiong with the previous captured trme, to calculate the rpm. Notice the ifstatement that checks for rollover; this is another method to allow for the case in which the 16-bit trmer/counter rolls over from OxFFFF to Or0000 during the elapsedperiod. The last statement in the ISR savesthe "current capture tine" for use as the'previous_ capiure-line" the ner.t time a pulse occurs. The rpm is being calculated as follovs: RPM = 1E6 micro seconds/second' 1 oulse / oeriod in micro-seconds * 2 revolutions per pulse'o0 secondsper minute Note that casting is used to ensure accuracywith the large numbers. Also, combining constants shortens the calculation formula. DRIVESHAFTRPMMEASUREMENT USINGTIMER I This measurementgets a litde bit more involved, becausethere is not a second capture register in the Mega16 and the shaft rpm signal is connected to 1NT0. You can üeate your own capture register within the INT0 ISR by reading the Timer 1 count when the interrupt occurs.Then the rest of the function wod<svery much like the one abovefor the engine rpm: unstqned interrup! int previous shaft capture_Eine; Eine /*saved /+capttte'/ T, te' upL 0 se!vice routine'/ isr(woid) I:EXT_INTo] voi(I ext int0 fron previous*/ Bl t32 unsiqned .. - int currents captsure time, / *currene period,. r t TCN-': rime e /'qet _-op. for ro11-over*/ ' .-pr urF prcvious_shotr_.dp ime -rc_ ^r^ , ra Lime previous shaft capture time, tine and* / /*eheck period current_s_rpn ple/ o.s.srd = oXFFFF currenr capLure rine c + = (unsiqneil lonq)60E6 / (unsicrned lonq)period; t_-dp.u 6_t mc -.urren.-cdptu,e .ime; /*nexE calcul ation*/ ) The calculation is the sarne,except that there is one pulse per revolution instead oftwo. A.1so note that some ofthe local variables have the same name. Since they are local, this is acceptable,but it is not acceptablewith some programing standards. 2.4 SERIAL COMMUNICATION USING THE USART Serial communication is the proc€ssofsending multiple bits of data over a single wire. It rs an offshoot ofthe original telegraph, in which the bits were the dots and dashesof Morse code.The bits ofa serial byte are separatedby time so that the receiving device can determine the logic levels of each bit The USART is used to communicate from the microcontroller to various other deviccs. Examples of such devices include üe terminal tool in CodeVisionA\ß. (used for troubleshooting and program debugging), other microcontmllers that need to communicate to control a system,or a PC that is communicating with the microcontroller to complete a task. The usual form ofserial conmunication, and the form being discussedherc,ts astnürana s serial communication. It is asynchronoush the sensethat a common clock signal is not requied at both the transmitter arrd the receiver in order to rynchronize the data detection. Asynchronous serial conmunication usesa stan bit and a stop bit added to the data byte to allow the receiver to determine the tirning of each bit. Figure 2-35 shows the elements of a standard asynchrcnous serial comrnunication bne. This ligure shows both the rvaveform and a defnition for each bit ofthe serial word. The serial trarsmit line idles at a logic 1 and drops to zero to indicare the beginning ofthe start bit. The start bit takes one tull bit time and is followed by the eight bits of the data blte that appear on the seial line in invene order, that is, the least significart bit appearsfrrst and the most signifcant bit appearslast. The stop bit follows the most signifcaat data bit and is a logic 1, the sameler"el as the idle stateThe falling edge ofthe start bit begins the timing sequencein the serial receiver Beginning from the falling edge of the stan biq the receiver waits 1.5 bit times before sampling the The Atn.l RISC Ptats!ar! 3 E a t n g E ä t I € 9 g '* z 6 E 133 B4 receiving line to get the fißt data bit- After that, the receiver$'aits 1 bit time per bit, therebv sampling each successivedata bit in the center of its time pcriod lor ma,ximum rcliabiliqr Fortunately, all of the timing relative to the serial blte formatting, thc sampling of thc sc rial bits, and the addition of the start stop bits are handlcd automatically by thc unioersal slnclronous asycbrcnos rc.e;eeFtransn,irer (USARI pronounced "you sart"). None of these issuesdirectly affects thc programmer. The only issueconftonting the progammer is to ensure that the scrial communication pa rameters ofboth the transmitter and the receiver rnatch. Spccificalll; this includ€s setting the corect number ofdata bits (usually8), determiningrvhcthcr or not to include a parig, bit (usually not), and setting the baud rate. The baud ratc is the speedofserial communica tion and determines the timing ofthe bits. Baud rate is defined as the imrrse of the time per bit (baudrate = 1/bit time)The serial war.eform and other parameters relating to the serial communication discussed above are all involved wit\ the ;nfamatiarbciog transmitted. The serial information is in dependent of the nediun being used to carry the serial information. The medium may con sist ofa wire. an inftaredbeam.a radio link. or oth€r means. The most common medium is defined as RS-232. It was dcvelooed in order to Drovide a greaterdistancefor reJiableserialcommunicationusingwire ro c;rv the signal.RS 232 is an inveted scheme,in that a logic 1 is reprcscntedby a negtive voltrge more negative than -3 V and a logic 0 is representedbv a positive voltage more positive than +3 V Using a dif ferent nonzero voltage for each logic level allows some hardware error checkng, becluse a brokenline will present0 V at the rcccivcrand so ma1'bedetected.Most microcontroller to-PC communicationis RS-232. CodeVisionAVR, like most C languagc compilers, provides built in library tunctions to handle the common serial communication tasks.These tasks usuallv involve communicat ing with a terminal device, for cxample, a PC executing a terminal program to transmit sedally the charactcrs qpcd on the keyboard and to display in a window the characters received serially from thc microcontroller. CodeVisionAVR prorndes a built-in terminal emulatorin the devclopmcntenüonment as a conenience to the programmer.The standard library functionsare includedin the headerfle stdio.h,rvhich may be includedin the C languageprogram. Using the header file with its built in tunctions makes serial communication very easy.T he erampleprograrnshorvnin Figurc 2 36 prints üe rnessage "Yrbba Dabba Do' on a termi nal der-ice. As the simple serial example shows,other than initializing the serial port (thc first trvo lincs ol nain)), serral conmtnication is ertrernely easyusing the built-in library functions. For more details on the Pinf) tunction, see Chapter 3, "Standard I/O and Prcproccssor Functions." Tbe Atne/ +incLude +incLude vold <nega16.h> <stdio.h> /* Standar(I Input/OuEpuE RISC Prateßaß functions*/ nain (void) I po.t initializedr/ / *serial taud rate* / /*ser UCR=0x18; printf whire ('\n\rYabba Dabba Do" ) ; /*prinL phrase*/ (1) /*do nothins elset/ ' Figure 2-36 SinpleSefialExol'l,ple The USART interface consists ofdree registers-These üe rhe USART contral arul status regi:ter, the UMRT baud rute reg^ttr, ^nd t\e USAPT data iegister.These rcglsteß may be either 8 or 16 bits in length depending on the complexity ofthe USART contained in the processorbeing used. (Nots in the simpler processors,the USART may be called a UART due to the fact that the peripheral cannot handle s).nchronouscommunications.) In the AIMegal6 for example, for norrnal asyndronous operatior\ the USART control and status register is a 16 bit register consisting oftwo 8-bit registers, UCJR 4 ^nd UCSRB, and the USART baud rate register is a 16-bit register consisting of {,ERR11and, UBRßI, which ar€ the high aüd low bytes, respectivdy, of I/3RR. For other modes of op€ration an additional USART control and status rcgister, UC,SRC is also available. Regardlessofthe processortype, the UDR is actually two registers sharing a single I/O address. One is a read-only register and one is a write only register. The read-only register contains ary seial blte received,and the wdt€-only register conuins any serial bye to be transmitted. So, when a program reads the IIDR" it is reading the receiver UDR to get data that hasbeen r€c€ivedserialbaWhen the program writes to the tansmitter UDR, it is wrring data to be serially transmifted. Figure 2-37 shows the bit definitions for the U&4R? eonfiol and statasregüte\ part B, ftom an ATMega16. UCSRB is used to initialize and set the firnction ofthe USART in the AIMeea16. The most signficant three bits are öe mask bits For the three int€nupts associakJwith the USART RXCIÄ is the mask bit for the intemrot which occurswh€n a s€rial chancter is rcceived by the USART TXCIE is the mask üit for the interupt thac occurs when the USART has successfr y completed transmitting ^ charao.e\ and UDRIE is the mask bit for the interupt that occlrrswhen the üansmit UDR is rexdy to tiansmit another charader. Refer to Figure 2-37 for other bits and how they affect the USART operation. t35 t36 RXC]E Bit 6 Bit 5 Bit 4 Bn -l Bn2 tsit1 Blr0 TXCIE IJDRIE RXEN TXEN UCSZ2 RXBS TXBS 8it RXCIE TXC]E UDRID Nlask bit for the Receive intetupt l,lask bit fo. the Tlmnit intetutt enablc. Sct to unmxsk the intedupt. ]\{6k bit for the UART Dxta Registd Rmpty i.ternpt en.b1e. Setto unmaskthc i.tempt. RXEN TXI]N UC5Z2 RXB8 TXBS Figure 2-37 cnablc. Set to unmask the interrupt. Ser ro €mble the eceivcr. "üJ Set to enäble the sdiat tnnsniftci Wnh UCSZl:o, seßnrnbd of datdbits. 9th bit rccciEd in 9-bitmode. 9th bit tü.smincd in 9-bit mode. AlMeEo l6 UCSRB In an AIMEGA16. UCSRA reflects thc curent status ofthe USART. The UCSRA con tains the intemrpt flag bits (most signficant 3 bits) and other bits that indicate the results o|USART activiry Figure 2-38 shows the bit definitions for the USR. The USART status is important due to the fact that serial communication is always slower than parallel communication. During the 1-04 milliseconds that it takes to transmit a single serial blte at 9600 baud, a microcontroller using a slstem clock of8 MHz can execute as many as 8000 instructions. So, in order for the microcontroller not to be waiting around lor the serial port (remember Real Time Processingfrom Chapter 1?), it is imPortänt for the program to be able to tell the state of the serial port.In the caseofa received character, it takes the same 1.04 milliseconds from the time the start bit is reccived until the character has been completely received.After the eighü bit is received,the PJC bit is set in the USR to indicate that a serial ble has been received-The program uses the RXC bit to know when to rcad valid data from the receir.eUDR. fie data must be read lrom th€ UDR before the next character is received,asitwill ove.write and destroy the data in the UDR. This explains the provision for an intermpt to occur when a setiäl character has been received so thrt it may be read prompdl' without consuming largc amounts ofprocessor timc Polling to seeif a blte hasbeen received, In a similar manner, the UDRE bit is used to indicate that the transmit UDR is empty and that another bJte may be loaded into the transmit UDR to be transmitted serially. Again, becausethe microcontroller can load out \tes much, much faster than thc this is necessa-ry USART can transmit them. In order to keep the program from har-ing to poll the USR Tle Atbel RISC Ptuestar! Bit 7 Bit 6 RXC TXC IJDRE Bir 4 Bit 3 Bit 2 Bir 1 Bir 0 FE DOR PE U2X MPCM 8it RXC TXC UDRE Set to indicarereipr of r sen,l chara.ter Set to indicate that a scrial charader has been sent. Set to indicateth.t the trdsnit UDR is en!+ FE DOR PE U2X I,IPCM Figure 2J8 Set to indicate a fiming üor Set to indicaE m om eror Set to double nansmi$ion sped. Set to en ble m! i-proc$. commüication mode. ATMegol6UCSRA continuoudy to seewhen it is amilable to send another byte, an intenupt is provided that indicates when the transmit UDR is emp+ The transmitter side ofthe USART is actually double buffered. That is, the UDR that the program writes to holds the data until the actual transmit register is emp+ Then the data from the UDR is transferred to the transmit register and begins to serially shift out on the transmit pin. At this point, the UDR is arailable to accept the nexr dara word lrom the pro gram, the UDRE flag is set high änd, ifenabled, the UDRE interupt occurs. Orcasionally, it is necessaryfor the miüocontroller to acnrally knowwhen a byte has been sent. The TXC flag is provided to indicate that the transmit register is empty and that no new data is warting to be transmitted. The program uses this fla& and its associatedintemrpt, when it is necessaryto know exacdy when the data has been sent. The frnal register associatedwith the USART is rhe I-ISARTbaud rate register,UBRR. Thrs register determines the baud rate at which the sedal port transmits and receivesdata. The number entered into the IIBRR is determined according to the following formula: UBRR = {Syslen clock / (16 } baudrate) ) - 1 Using this lormula,the UBRR numberfor the previousexample(Figure2 36) is calculated asfollows: UBRR = = (Systen (aMHz / Clock / (16 * baudrate) ) - 1 (16'9600 baud)) - 1= 51 = 0x33 t37 t38 In this example,UBRRL is set to 0x33 and UBRRH is set to 0x00' The high bJte of the value is placed in UBRRH, and the 1owb1,teof the value is placed into UBRRL. Microcontrollers often need minimum amounts of serialcommunication but do not need all ofthe formatting options and other featuresincluded in the standardlibrary functions. The standard library functions also consume large amounts of program memory. In these cases,the programmer must implement the serial communication. Figures 2-39 and 2-40 show hardware and software, respectively,for a simple system to implement serial communicationsbetweena microcontrollerand a PC using RS-232. Figure 2-39 shows a standard AVR processorwith an attached MAX233 media driver to convert the TTL serial signals used by the microcontroller into the RS-232 signals used for serial communication to the PC. The hardware shown in this figure is used with the software shown in Figure 2-40 to make the serial communication example. The serial communication example software is a Program (Figure 2-40) that usesa switch construct to print one of three messageson the PC. The exact messagewill depend on whether an "a", a "b", or anotherkey is pressedon the PC' The ASCII codefor the character pressedis sent seriallyto the microcontroller.This exampledemonstratesboth manual and interupt handling of USART functions. RESET VCC avcc ADC'IIPAT AOC6/PA6 ADC'PAs ADC4/PA4 ADCSPA3 AdatPA2 ADC1/PA1 AOCo/PA0 SCKPBT Mt60/Ps6 M06UP95 SS/PB,l oco/AtN1/PB3 T1/PB1 XCKTO/PBO xrALl XTAL2 AGND GNO OCZPDT tcPl/PD6 oclaJPos 0C1B/PO4 tNTl/PO3 tNl!/PD2 TXO/PD1 RXO/PDO TOSC2/rcT TOSCtPC6 tDtPc5 'rDo/Pc! 'IMsFC3 rcKPc2 SONPC1 €cuPc0 I\,IEGAl6 Figure 2-39 SerialCommunicotionExompleHardwore T1IN T1OUT T2]N T2OIIT c1+ c2+ c2+ D89 _1 ,-i | -: l=ä &o-" Tbe lttel +include <necra16.h> unsisned unsisned char chai = orsndcntr qcntr queuet50l; a!lays'/ /*nessage = {"That char nsqlll = liThat char nsq2tl = {'That cha! nsq3tl = 0; inro /*indexes queue*/ /rcharacte. sas an a-'i, was a b, not an a-'l; was neither b no! a. lhe RISC Pro.alor! quer/ l; inteüupt occuls whenewer the */ /*this h a s c o n p l e t e d s e n dinq a character*/ /*USART isi intetupt usart_transnit [usART TxC]woid (void) t nexE character /*send (qcnt! if l= sndcntr) and increnent lnalex*/ UDR = queuelsnalcntr++l; ) function loads rhe queue /*this the sending plocesst/ / *starLs (char *s) void sendnsg and t/ { = 0; qcntr indices*/ /*preset = 1; atready to one because firsE character sndcnrr /'set = 0x0al; queue tqcnrr++l CRLF into Ehe queue firsL*/ /*put queue Iqcntr++ ] = 0x0a; = +s++; ('s) queuelqcnLr++l characrers into /*pur shiLe p!ocessr q.F.al0.; li'st .h-räclFr lo slärf UDP /'send sent*/ queue*/ l nain (vold) void { wariable for received char ch; /r character UCSRA=0x00; .eceiver, transmittser 4d UCSRB=oX58; /*edable UBRRH=oXoo, /*L'aud rate = 9600'/ UBRRL=0x26; #asn("sei') while /*q1oba1 inrerrupt enable character*/ transnit */ (1) t if (UCSRA & 0x80) ch : üDR; switch i ch) i /*check /"get for characEer receiwed*/ cbaracte! sent fron FiSur€ 2-,10 SefiolConnuni@tin Exonptesoftwore(Contnues) Pc*/ intefiup!*/ 139 t40 Figure 2-40 sendnsq (msgt ) i /'send fi-sl s e n d n s q ( m s q 2) : /'send se.ond sendmss (nsq3 ) ; /*send defaull nessdg^' messaS6! messaqe*/ SerialConnunicotionExomphSoftworc(Conünued) The first five lines in maino declare the character variable and initialize the USART. UCSRB is loaded with &58 to enable the receiver-the transmitter. and the transmit intcrrupt. The UBRR is set to Ox33to set the baud rate to 9600. Once the USART is set up and the interrupt is enabled, the program enten a tal/a1'l loop that continuoudy checks for a receivedcharacter using an ifstat€ment whos€ the expressionwill evaluateto TRUE after a character is received.Receiving the character will set the RXC bit in the USR that is being tested by the if statem€nt.This is an exampleofmanually polling the statusofthe serial port to determine when a character is received-TXC could be used in a similar manner to poll for the conclusion of a transmission. When the if statement determines that a character has been received, the character is read ftom the UDR and used in a switch statement to determine which messaeeto send. The messagebeing transmitted(i.e.,"That was an a.") is composedof severaliharacten. each ofwhich must be sent serially to the PC along wit\ a carriage retarn (CR) and t l;nefeed (ZF) character so that each messag€will start on a new line. The longest messageis composed of25 characters,and adding the CR and LF charactersmakes the total message27 characterslong. At 9600 baud (1.04 ms per serial byte), this messagewill take over 27 mi1liseconds to transmit.It is not appropriate for the microcontroller to wait around for 27 mi1liseconds, becauseit could be executing as many as 216,000 instuctions (8 instructions per microsecond * 27 milliseconds * 1000 microseconds oer milliseconds = 216.000 instructions) while this messageis being sent.In order m ftee the microcontroller ofthe need to wait while the messageis being seng a FIFO qu6ue is used in conjuoction with the transmit inteIfupt to acnrrlly transmit the message. A queue is a temporary holding device to hold bytes ofdata and retum them on a 6rst-io, tust-out (FIFO) basis. In this case, the queue is mechanized as a variable array of data called, appropriately, qzere. An index is used to indicate where new data is to be placed in the queue (in this casegczrr). As each new blte is added to the queue, the index is incremented so the rext blte is added in sequenceand so on untit the queue holds all ofthe nec- The Arn.l RISC Pta,t)'at t A sepxrxte index (in this case,rrlrnt) is us€d to rctrieve the data from the queue. As each blte is retrieved, this irdex is increnented. Finall,r.,when the trvo indices are equal, thc program knows that the queue has been emptied. Actua11y,the CodeVisionÄVR C language compiler can provide a transmitte( queue, x receiver queue, or both using the "CodcWizard" code genuator feature. This cxample is provided to demonstrate holv the queue works for cducational reasons. Getting back to thc example program, the sazlnrrglJ tunction called fron the switch state ment puts the mcssageinto the queueand startsthe üansmit function.The switch statc ment passesa pointcr (an address) to the appropriate messagcwhen it calls the tunction. The function lirst puts the CR and LF characteß into the queuc and then Puts the message to be transmitted into the queue using the pointer. Finally the function writes the 6rst byte in the queue into the UDR to scart the transmission process.After this character has been transmitted, the TXC inte upt occurs and the ISR loads the next character from the queue into the UDR, irnd so the c1'clccontinues until the queue is emptv, as indicated b)' the two indices being equal. A morc claborate form of the queue tunction rvith addnional explanr tion may be lound in Chapter 3, "Standard VD arrd PreprocessorFunctions." 2.9 ANALOG INTERFACES In spitc of thc prevalenceofdigital devices,the world is still actually analog by naturc. A rttI crocontrollcr is able to handle analog data by first convening the datä to digital form. An A\rI{ microcontroller includes both an analog to digital c'onversionperipheral and an ana1ogcomparatorperipheral.Each of theseanalogintcrfaceswil1be coveredin this scction, along with a briefbackground on analog to digital conversion. X/ticrocontrollers use analog to digital conveners to convert analog quantities such as tem perature and voltage (for examplc, a lorbattery monitor), to convert audio to digital formats,and to perform a host of additionalfunctions. 2.9.I ANALOG-TO-DIGITAL BACKGROUND Analog-to-digital conversion (as rvcll as digital-to-analog conversion) is largely a matter of (ADC) ?r0Portion.Thatis, the digital number provided by the analog to digital converter relates to the proportion that th€ input voltage is of the ftlI voltage rangc of the converter. For instance, appl,ving 2 V to the input of an ADC with a fi -scale range of 5 V will result in a digital output that is,10 percent of the tull rangc ofthe digital ougut (2 V / 5 V = 0.4). ADCs are available that havc a Erielv of input voltage ranges and output digital ranges in terms ofbits, suchas 8 bits or 10 bits.The The output digital rangesareusuallyexpressed number ofbits at the output determinesthe range of numbersthat can be read ftom the output of the converter. An 8 bit converter will provide outputs ftom 0 up to 23 - 1 or 255, and a 10-bit convertcr will pror.ide outputs from 0 up to 2ro 1 or 1023. In thc prcvious e{ample, in which 2 V was applicd to a converter with a lirll scalerange of 5 V an 8 bit converterrvould read 40 percentof255, or 102.The proportion/conversion t4 t42 factor is summarized in the following formula: V; 2"-l In the formula above,".r" is the digital output and h" is the number ofbits in the digital output. Using this tormula and solving for a you can catculate the digital number read by the computer for any given input voltage. Using th€ formula witlin a program where you have r', you can use the formula to solve for the voltage being applied. This is usetul when you might be trying to display the acturl voltage on an LCD readout. An important issueburied in this formula is the issue ofrcsolution- The resolution ofmeasurement, or the 6nest increment that can be measured,is calculated as followsr Vr.tot 2"1 For an 8-bit converter that has a full-scale input range of5 V, the resolution would be calculated as follows: V--r";- = 5V(2o 1) = 5Vl255 = 20 mV (approx.) Therefore, the linest voltage increment that can be measuredin this situation is 20 mV It would be inappropriate to aftempt to make m€asurementsthat are, for e{ample, accurateto within 5 mV with this converter. 2.9.2 ANALOG.TO-DIGITAL CONVERTERPERIPHERAL The ADC peripheral in the AVR microcontrollers is capable of 10-bit rcsolution and can operate at speedsas high as 15 kSPS (kilo-samples per second). It can read the voltage on one ofeight different input pins ofthe microcontroller, meaning that it is capable ofreading fiom eight different analog sources. Two registers control the analog to-digital convener: The IDC contral and stahß rerbter (A-DCSRA), conüols the tunctioning of the ADC, nd the ADC nuhipkxeßek{t rßiter (ADMUX), controls which of the eight possible inputs are being measu-red.Figure 2-.11 shows the bit def,nitions for the ADC conrol and status register. The ADC requires a dock frequency in the range of50 kHz to 200 ktlz to operate at mrr( imum resolution. Higher clock fuquencies are allowed but at decreasedresolution. The ADC clock is derived from the s,-stemdock by means ofa prescalerin a manner similar to the timers. The lemt signficant three bits ofADCSRA control the prescalerdivision ratio. These bits must be set so that the s)stem dod<, when divided by the selecteddivision raoo, provides an ADC clock between 50 kHz and 200 kHz. The selection bits and division ra tios are shown in Figure 2-42. Although it could be done by trial and eror, the most direct method for choosing the ADC T b e , 4 ! m ? l P . I S CP n t e " a l t Bi7 Bit 6 Bit 5 Bit 4 Bit 3 Blrz Bit I ADEN ADSC ADAIE ADIF ADIE ADP52 ADPSl Bit 0 ADPSO ait ADEN ADC Dnalrlebit. Set to cnablethe ÄDC- ADSC ADC Stan Conysion ADC Fre Rumiü. Selectbit. Setto eDablcftcc ron mode. ADATE AD]I AnC Intempt l'l,g bit. ls set by htrdlld at the end of a convcsion c}cle. Ä DC lntenpt Masl<bir Set to a]lN the intmpt to omr at the end of a convcson. ADIE ADP52 ADPSl ADPSO Figure 2-4 | bit Ser to start a @nversion. ADC Pesc,ler sdtrr biß. 8it Defnitio,s ADCSRA preselector factor is to divide the system dock by 200 kllz and then choose the next higher division factor This will ensurean ADC do& that is as fast aspossiblebut under 200 kHz. The ADC,like the serial USART, is somewhat slower than the processor.If the processor were to wait for each analog convenion to be complete, it would be wasting valuable time. As a result, the ADC is usually used in an interupt-driven mode. Although the discussion thxt follows usesthe more common intermpt driven mode, it is also possible for thc ADC to operate in ftee-running mode, in which it contiouously does conversions as fast as possible.lÄ.hen reading the ADC output in free running mode, it is ADPSI 0 0 0 0 0 1 0 0 0 L 0 I I ADC Preselector DtistonRoltos bii.i;'; 2 2 0 8 1 1 Figure 242 ADPSO 0 32 12rJ 143 necessaryto disable the intermpts or stop the free running conversions,read the result, and then re-enable the interrupts and free-mnning mode. These steps are necessaryto ensure that the data read is accurate,in that the pmgßm will not be reading the data during the time that the processoris updating the ADC result registers. The ADC is usually initialized as follows: L Set the tiree lowest bits ofADCSR for the correct divisionfactor. 2. SetAD|Ehighto enableinterruptmode. 3. SetADENhighto enableADC. 4. SetADSC!o immediar€ly srarraconversion. For a division factor of8, the following lines of code would initialize the ADC to read the analog voltage on the ADC2 pin: ADMUX = 2; /*read analoq voltaqe on aDC2r/ /"ADc on, iaterrupr noale, /8, & starEed*/ The initialization above sets up the ADC, enables it, and starts the 6rst conversion all at once. This is useful becausethe fust conversion cycl€ after the ADC is enabled is an exlra Iong cycle to allow for the setup time of tle ADC. The long cyde, then, occurs during the balance ofthe program initialization, and the ADC interupr will occur immediately after the global interrupt enabled bit is set. Notice that the ADMUX r€gister is loaded with the number of the ADC channel to be read. Figures 2-43 and 2-44 show the hardware arrd software, respectively,for a limit detector systembased on the analog input voltage to ADC channel 3. Briefly, the system lights the red LED ifthe input voltage exceeds3 V, lighs the yellow LED ifthe input voltage is below 2 V, or lights the green LED if the input voltage is within the range of2 V to 3 V The limit detector program in Figure 2 44 shows a g?icat application for the ADC. The ADC is initialized and started in nainqby seüngADCSRA to 0xCE. ADC channel3 is selectedby sening ADA4IX to 3. This starts the processso the ADC interupt will occur at the end ofthe frst conwrsion. Checking the ADC outpur to seewhich LED to light xnd lighting the appropriate LED are all handled in rhe ADC interrupt ISR. Notice that the 10 bit output ftom the ADC is read by reading the data from ADCW ADCW is a pseudo register provided by CodeVisionAVR that allows retrieving the data from the two ADC result registers, ADCL and ADCH, at once. Other compilen would more likely require the programmer to read both ADC registers (in the conect order, even) and combine them in the 10-bit result as a part ofthe program. AJso notice that the programmer has used the analog to digital conversion formula in the ISR. The compiler will do the math and create a constanr that will actually be used in the program. You will frnd that this technique can be used to ]rcur advantäge in several other places,sucl as loading the UBRR for the US$T. The ADC peripheral in the AVR microcontrollers varies somewhat according to the spe- The Atnel aotaTtPAT ADC6/PA6 ADC5/PA5 aota4tPA4 AOC3PA3 Aoc?lPA2 aocl/PA1 aoco/PA0 RESET vcc AVCC AREF c4 SCKPBT MISO/PB6 MOS/P85 ssP9l oco/AtN1Fs3 INTZAINC'PS2 T'PB1 XCKTO/PBO r|AL1 TAL2 AGNO GNO t3<:2r,o7 tcPl/P08 oclArFOS OC1B/PD4 INTl/PD3 INTO/PD2 TXD/PD1 RXO/PDO TOSC2PCT TOSCl/PC6 T0uPc5 TDO/PC4 'IMgPC3 TCK/PC2 SDNPCI scuPco Figure 2-43 ADCExomple Hardwore <mega16 .h> #include /-Define output po-rL and -Iight *detfne L!jDS PuKlc #define red 0b11011111 +defilre yelIow types'/ 0b10111111 /*ADc rsR, reads ADc, sets lights*/ i nterrupt IADC_INTl voi d adc isr (void) t rnsidre.l inf ä.i. dätä: for ADC results*/ /*variable 10 bits into variable*/ adc_data = ADCW; /*read all (adc-data > 13*L023) /5) if { LEDS = , /* t o o red; high ) el se if i Figure 244 (adc_data < (2'7023J /5) ADCExompleSoftwore(Cont)nu*) (>3V) *,/ RISC Pracessors t45 146 LEDS = Yellow; /*Loo aow (<2vl'/ l { LEDS = sreen, /tnusE be jusr aDcsRA = aDcsRA I 0x40; righr /tsEart - like coldilock,s the nexr conversion po.ridge*/ */ ) void nain (void) { D D P C- 0 x e o ; A D M U X= 0 x 3 ; ADCSRA=oxCE; +asn("sei") while : J birs ro- o.Lp.r' /.mosE siqnificant /'selecE to read only channel 3*/ unnasked, and started*/ /+ADC ot, /64, inlerrupt /*stobal inEe4upt enable bir*/ (1) 7 do -oLhinq but wait on ADc inrerrupr -/ ) Figure 2-,44 ADC Exonple Softwote (Contnued) cific microcontroller in use. All of the ADCs reSuire sorne noise suppressionon the ADC Vcc connection (seeFigure 243 or 2-46). Some a1sohave a built-in noise canceller function, and some have the ability to control Vrefintematly. You will need to check the specification for your particular microcontroller when using the ADC. 2.9.3 ANALOGCOMPARATORPERIPHERAL The analog comparator peripheral is a device that comparestwo analog inputs: AINO, the positive analog comparator inpu! and AIN1, the negatir.e analog compuator input. If AINo > AIN1, then the analog eon?arutor oltfd bit (ACO) is ser When the ACO bit chang€s state, either positi\€ goin& negative-going, or both, it will cause an inteffupt to occur, provided that the analog comparator intemrpt is unmasked, or else the charge of state may be set to causean input capture to occur on timer/counter 1. The analogcon?alator co11trcland stutusreg;ster(ACSR) shown in Figure 2-45, is used to control the analog comparator functions. As a simple example ofanalog comparator funaioning, consider the sl.rstemshown in Figure 2 46. A battery is used to power the system, so it is important to know when the battery voltage becomesdangerously low. Tbe.4tnet ßISC Pturetsaü Bir 7 Bn6 ACD ACBG ACO Bit 4 Bit 3 B,t2 Bn1 Bit 0 ACt ACIE AC]C ACISl ACISO 8ir ACD ACBO ACO ACI An.log Comp@tor Disäble bit Set to disable the dalog conpantor Ä'atog Compmtor Analos Compmbr Outpüt bn. Ann% Comnmtor lntmpt f ,9. maskbit. Analos Cofrpmtor I'tmpt AC]E ACIC ACISl ACISO bandgap rclcd. An t% Con?dator Input CaptE bit. Sct to enable iryut apture or compmtor chmge of*tate. Analog Coßrrter Compdator Mode Select bits(See definitions belos) AndlogCom\orelnteftuptModesele.t BirDefritons: Äcrst acts9 Com?,ßtorinrmFun Resc(cd ACO rogglc. do not use. 1 Conpdator intempt on ACO li ing edgc. (AIN1 b@om6 sread than AlNo.) 1 Conpdator intcmp! on ACO rising edgc. (AINo bccomes sreate. th.n AINI.) Figure 2-45 ÄCSR8,t D€fniliotrs The slstem shown in Figure 2-46 is continuously monitoring the battery without expending any processor time whatsoever, because it is all handled by thc analog comparator. When the battery \.oltage becomestoo low, the LDD is lighted. The two analog conr.crter inputs are connected to voltage dividcrs: one is powered b]' the regulated +5 V as a refcrence, and the other is powered direcdy by the battery The voltage divider powered by the +5 V is designed to provide approximately 2.2 V at its center Point The other voltage divider is designed so that when the battery dischargesto approximatcly 6 V, the center point ofthe voltage divider will also measureapproximately 2.2 V The analog comparator is set to detect when the voltage from the battcry's voltage dividcr drops below the 2.2 V providcd b1,the referencedivider As Figure 2 47 shows, using the analog comparator is relatively simple ln this example' ACSR is loadedwith Ox0A to enablcthe analogcompararor,coenableits jntcnupt and to t,{8 ADCT/PA7 AOC6/PA6 ADC'PAs AOC4/PA4 AOC3/PA3 ADC2/PA2 ADC1/PA1 ADCO/PAO RESET VCC AVCC AREF 'T 'I SCKPBT M|SO/PS6 MOSI/PB5 ss/PB4 oco/AtN1/PB3 INTZAINC'/PB2 11/PB1 XCK/TO/PBO I I ,v,. AGND GNO 70sc2!Pc7 TOSCl/PC6 TDUPCs TDO/PC4 TIVIS/PC3 TCI(PC2 SDdPCI SCUP@ MEGA16 Figure 2-46 AnologComparotor ExompleHardwore <mega16 . h> #include +define L E D P O R T C .0 unsigned int blink_count /* Analog interrupc = 0; /*counter for LED blinker*/ Comparator interrupt service routine*/ IANA_COMPI void ana_comp_isr{woid) t ACSR = 0; /*disable TCCRo = 0x5; /*start the the comparaLor*/ timer*/ 1 /+ Timer incerrupc 0 overflow interrupc service rouEine*/ ITIMo_OVF] void timer0_ovf_is-r(void) { TCNTo = 256 - 6; for approx. 1ms overflow /*set ++blink_counE; / +incremenE blink counter*/ s\4'i tch { bl ink_count ) { Figure 247 AnologComporctorExampleSoftware(Conünues) rate*/ The Attu,/ LED = LED = blink 0,' /*LED oEr/ I; / tIrED off+/ count break; = 0; blink /*reseL /taio nothlng RISC Pntüsars counrer*/ */ ] void nain (void) t LED off*/ vilh PoRTC = 0x01; /*start t,iE 1 for output*/ DDRC = 0x01; /*sel analog conp, enabte conparaLor /*enable TIMSK = 0x01; +asn('sei ; /"do ) nothinS /*unnask /*set slobal Tiner interrupt, 0 overfloe intelrupE inportantly, fallinef edqe*/ interrupL*/ enable put bit*/ operational code here*/ ] Figure 247 AnalogConporctotExonpteSoftuorc(Continued) set it so that the inteffupt ocürs on a falling edge when AIN0 drops below AIN1 (AIN1 becomesgreater than AINO). Thc AC ISR starrcTimer0, which is set up to blink the LED on for 10 ms out of every 2 seconds.This blink is designed to show the baftery condition while minimizing the additional current draw due to tlre LED. Äfter all, the battery is loq so we need to protect what is left ofthe battery power. The AC ISR also disablesthe analog comparator This is important to be sure thät noise or other instability of the battery voltage rvill not causeeffatic blinkhg on the LED. Chapter 2 Example Proiectr Part D This is the fourth part ofthe Chapter 2 example using a stock car datn collection system This portion is concernedwith measuring the engine temperature ,nd sending the collecte,l datato the PC. USINGTHEANALOG-TO.DIGITAL MEASURING ENGINETEMPERATURE coNvERTER (ADC) Previous investigation showed that the temperature signat is connected to ADC3, the ADC input on Port A, pin 3. Some firther in estigtion using the specfication for the RTD ther mocouple and the circuitry conditioning the RID signrl shows that the measurementmnge is, happily, exacdy the range your bosswants, 100T to 250T- Using tlre 10 bit measurement t49 t50 mode on the ADC means that the resultins measuredvalu€sr-ill be as folows: 100"F= 250'F = 0x000 = 0,0 0x3FF = 1023r This setsthe convcrsionformula to be + 100'F Temp = (150'F- ADcreadins)/1o23 Thc ADC may most conveniendy bc run in lree running mode for this usc. In this rvay,the tcrnperature *'ill be kept up to date as last as possible so that rvhen the data is stored at the onc secondinterval,the most recentvaluewill be recorded.In free-runningmode,the ADC interrupt occurs at the end ofcach conversion and can be usedto update the curent temperP:rt of thc ADC initialization is to selectan appropriateclock frequencyby choosingthc prescalervaluefor the ADC clock The ADC clock must be between50 kHz ancl200kHz. In this case,you havea systemclock of8 I\4H2, and so a prescalerof6,1will give an ADC clock of125 kHz TheADC initi:lization proccssinr.olveschoosingthe channelto be measured,enablingthe fiee running mode, and starting the fust cofl€rsion so that an inteffIpt rvill occur at the end of the conversion,keepingthe processrunning: ÄDl.lux=oxl; /*select channel 3 and ÄREF pi. as the referen.€ volraqe*/ ,'* inpur* / ADCSRA=oxE9; /-enable ADc, free run, slarred, clock prescaLer of 64*/ The ADC ISR has the job of reading the current conversionv.rlueand convertingit to /* ÄDC inierrupt rDc \ selvice routine-/ I vo. r cd- :si (voio) unsiqned int ÄDC_DATÄ; ADC DATÄ = ADCITJ; /*get data iron ÄDC resuLr * (long)ADc DATA)/ curient tenp = ((lonq)150 (1ons) 100; reqistefr/ (Lonq) 1023 ] SENDINGCOLLECTED DATATOTHE PC The co ected data is drcady converted to units of rpm and .ll so this tunction needs only to send the data to a PC. This involves initializing the USART and using built in firnctions to Iormat md sendthe data. The USART is initializedfor 9600 baud,8 bits, and no parigvasfollorvs: /+ UÄRT ini LiaLization r/ 1'h AInel RISC Pn.A'at ' transmitier /* enable 9600 baud*/ /*seleci] UCSRB=oI18; UBRR=023 , UBRRHI=0x0 0; and leceiwer r/ The data sent to the PC is going to be analyzed using a Microsoft Excel spreadsheet.Investigation shows that data can be input direcdy using a comma delimited (CSV) format. This means that commas separatethe data on each line ofthe spreadshcet,and CR separateseachline.That is, datasentas data1,datl, data3 data4, datas, data6 will appear in the spreadsheetexactly as shown above occupying a spacetwo cells high by three cells wide. In this case,1ou decide that the fust column in the spreadsheetwill contain the engine rpm, the second will contain the shaft rpm, and the thnd will contain the engine tenperature. Each line ofthe spreadsheetwill contain one set ofdata, so each line will contain data taken one second afier the data in the previous line. The following code 1st\,e uh;h(1) ftom the nain) tunctiot of t\e code: if ( r p r N A . 0) /*nobe: switch nusE be released before data is*/ t unsigned char x; /rtenporary tittes into colum ("gs , gs , *s \n', 'Tenperature" ) ,. (x = 0; x < 120,. x++) /*plinE printf for I /* prinL pr:n-t counter variable*/ in the first the spreadsheet Engine RPM". "shaft RpM', one seL of alata inEo one line gd {"9d, sd \" ,e- palxl, row*/ on the spreadsheeta/ römptrl': s -pm xl. ) This routine sends the 120 sets of data (and a line of column tides) using the builtln pintf) tuncnon. A neul;za character (anl is included with each set ofdata to causethe nexl set to appear in the following line ofthe spreadsheet 2.I O SERIAL COMMUNIGATION USING THE SPI ^the serial?ei?heftt ;nttf.tra, SPI (pronounced ipy"), is another form of serial communi cation available in the AVR microcontrollers. It is a synclronous serial communication bus, meanine that the transmitter and receiver involved in SPI communication must use the sameclock to svnchronize the detection ofthe bits at the receiver.Normall* the SPI bus is I5l t52 used for very sho.t distance communication with peripherals or other micrccootrolleß that are located on the same circuit board or at least within the samepiece of hardware. This is different fiom the USARI, which is used for communication over longer distances,such as between units or between a microcontroller and PC. The SPI bus was develooed to orovide relativelyhigh-speed,short distancecommunicarionusing a mjnjmum nu.t.t oirrl;..ocontroller pins. SPI communication involves a master and a slar,-e. Both the master and a slavesend and rcceive data simultaneously,but the master is responsiblefor prcviding the clock signal for the data transfer. In this way the master has control ofthe speed ofdata transfer and is, there fore, in control of the data transf€r Figure 2-48 shows the connections between the master and th€ slave units for SPI communication. The master supplies the dock and eight birs ofdata, which are shifted out of lrc master-out-slau-in (MOSI) pin. The sameeight birs xre shifted into the slaveunit, one bit per clock pulse, on its MOSI line. As the eight bits are shifted out ofthe master and into the slave,eight bits are älso sbifted out ofthe slave onits master-in-slate-arz (MISO) line and into the master on its MISO pin. SPI communication, then, is essentially a circle rn which eight bits flow from the master to the slaveaJlda different set ofeight bits flo\\.s from the slave to the master. In this way, the master and a slave can enchangedata in a single It is entirely possible to connect many different devicestogether using a SPI bus, becausea1l ofthe MOSI pins and all ofthe MISO pins could be hooked together. Alry device on the network can become a master by simply deciding to send data. A device on the network becomes a sla\.ewhen its Jazr selacr(SS) pin is grounded- Usually, the SS pins fiom the slaves ^4dner ShiF ReSiner MSB LSB CLK CLK SS MSB MISO Figure 2-,f8 SPIConmunkation khet|ie T b t 1 ! n , P lR l S t P a , . . " a ' BitT Bit6 SPIE SPE Bit5 Bit4 Bit3 Bn2 DORD MSTR CPOL CPHA Bitl tsito SPRl SPRO ait SPIE SPI Int@pt Mdk bit SPE SPI Enablcbir. Set to 6able SPI opmtiotr- DORD Data Order bit. Cleded caucs the MSB of the datarvord to bc t msmitted 6ßt. MSTR CPOL CPHA SPRl SPRO Mßter/SlaF Seled bir. Sel foi the dd;( robe üe mb,a. Clock Poldiw bit. SPI ClGk Rarebits (w tablc b€lN). sP, clo.k Rote Bit Detritliorsl SPRI SPRO SCIK fr€quer.y Selecr 0 I I 0 S)s:tenClock / 128 1 Figure 2-49 SPCR BftDeltni'ons a-reconnected to either a parallel port on the master or to a decoder that determines which device will be the slave. The SPI eontrolregbter, SPCR, controls the operation ofthe SPI interface. SPCR bit deflnitions are shoun in Figure 2-49.In a similar manner to the control registers studied pre viously, there are bits to enable the SPI interface lnd its associatedinterfupt, arld bits to control the communication speed.There is also a bit to set when a device is acting as the master,MSTR. In addition, there are bits to control the data order, MSB 6rst or LSB 6nt, and to selectthe clock polarity and the dock phase.These bits are used when matching the SPI communication peripheral to other SPI devices. Figures 2 50 through 2-53 show the hardware and sofiware for a simple SPI demonstra tion system. The s'stem reads the switch data &om the dip switch on one system and 153 t54 RESET vcc avcc AREF xrALl XTAL2 AGND GNO AOCTtPAT ADC6/PA6 ADCtPt5 ADC4/PA4 ADC3/PA3 ADCA?tC aDcl/PAl ADCO/PAO scKPsT Mlso/PB6 MOSUPB5 ss/Pa4 oco/atN1/P83 INl2'AINO/PB2 T1/PB1 xcK/ro/PB0 oczPDl tcPl/PD6 oclt/PDs 0c1&PD4 INTl/PD3 INTOPD2 TXC'PD1 RXC'PDO 7A€cZPC7 TOSC1/PC6 ]Dt/PC5 TDO/rc4 TMgrc3 lCKtPC2 SDAJrc1 SCUrcO Figure 2-50 ATMega | 6 sPl Demonstrotion SystemHordwore displays the switch data on the other system, and vice versa.All communication takes place via the SPI bus. The Atmegal28 is the SPI Master, and the ÄIMega16 is the SPI slave. The Atmega128 readsthe data to be sent from the dip switcheson PORT F and sendsit to the AIMegal6 slave,where it is displayedon PORT C. At the same time, the data from the AIMegal6 (from the dip switch on PORT A) is returned to the ATMega128 and displayedon its PORT A. The systemcontinuously updates,making it appearto be instantaneous. PORT B (PORT B alternatefunctions include the SPI pins) on eachprocessoris initialized as shorm below: Pin MOSI MISO SrovePORTB ,lMosterPORT B Input Output Output Input SCK Input Output SS Input Output Tle Atmel RISC Processors Ntso MOSI ss GND PFI(AOCTNDD PF3(AOC6'4OO) PFqaDcsrMs) PF4(a0c.{/rcK PF3(Aoca) PF2(ar4 ^ PFi(aocr) z PF0{a0c0) I 0 (C3IMT4PE7 O3/NTEPE€ (ocao$noPEs (oc3BnNr4)PE4 (ocaararNl)PE3 ßcKo'arNorPE) [xDlPDo)PEl (Fuo/Po)PEo Hordwore Figure 2-5 I ATMegol2SSPIDemonstrotion The definition of master and slaye is refected in the port initializations. It also allows a direct connection (MOSI-MOSI, MISO-MISO, SCK-SCK, and SS-SS).The ports are initialized, and the SPI systemis enabled,along with its interupt, in the main)Ioop. Following the initial.izations, there is a short assemblycode routine automatically inserted by CodeVisionAVR that makessurethat the SPI interrupt is cleared.This is an important step to be sure that the SPI interrupt serviceroutine does not executeuntil you intend it to. Fina11y, Ox00is written to SPDR to start the SPI communicationprocess. Once started,the entire function is handled in the SPI ISR functions.The master'sISR readsthe data received and writes it to the output port (the LEDs). Then it readsthe input port (the dip switch) and starts a new communication cycle by writing the data from the t55 t56 /*SPI sLawe codet/ <nega16.h> *include #define *define SPI SPI output_data input data PORTC PINA /* sPI inter.upts servlce intefiupt void ISPI,STC] routiner/ (woid) spi_isr { SPI ouLput data = -SPDR; /*read SPDR = SPI input_data; /r1oad ns out new data received*/ data for NEXT comunicarion cycle+/ l void { nain(woid) DDRB= 0x40; /*sclk, MOSr, SS = inpur, MISO = ourput*/ DDRC = oxFF; outputr/ /*a1t PORTA = oxFF; ups for dip swiEch*/ /tpu11 SPCR=oXC1; /*enable SPI, and its inEerupr, I D.ovidpd by codevisionAVR fo rteär rhe SpI in slave node*/ incer!!p| tä9. 130, spsr rru, spqr +asn('sei" while ) // clobal enat'te interruprs (1) { I ] Figure 2-52 SPISlaveSoft1,,ote Exonde *include #define #define <neqa128 -h> SPI output_data SPI input data /* spl ioterrupE serwice interrupt ISPI STcl void PORTA PINF routine*/ spi,isr(void) { P O R T B -0 = 1 ; /*ss hiSh*/ = -SPDR,. /*read SPI output_data daEa fron last PORTB.0 = 0; /"lower SS*/ SPDR = SPI input data; /'send ne, data out*/ J Figure 2J3 SPIMostetSoftwarcE anpte (ConnnueE exchanse*/ TheArnel RISC Ptote)!aü // your Declale qlobal void main (void) I PoRTA=oXFF; DDRA=oXFF; PORTB= 0x01, DDRB=Oao1r PoRTF=oXFF; L\- in in here with LED s off*/ /;start output, / /,all wich SS hiqh*/ /*srarr /*ss, sck, and MOSI as outputr/ /*pu11 ups for dip ssitch*/ SPCR=oXD1; SPSR=0x00; .l-- variables /*l?5 sP KHz c1ock, inLFrrupl enable sPI, sPI inlerrupi*/ fldg 130, spsr 130, spdr +asn('sei') SPDR = 0x00; whire /*write once Lo start [processi/ (1) t ; /*Place oEher code heret/ ]; Figure 2-53 SP,/vlosterSofworeExomp,e input port to SPDR. The slavelSR then merely acceptsthe new data and provides its olun switch data for the nert communication cycle. And the cyde repeatsforever. An important concept to note is that the data going from the slaveto the master is actually one cycle bebind the data going to the dar.e.This occurs becausethe slaveloads new data 4frr it receivesdata from the master. The SPI bus is often used to form a high speed network within a device.The connections rnay be parallel (a11the MISO pins tied together and all ofthe MOSI pias tied together) or in a large serial loop, where all of the data bits travel through all the devicesin turn in a man ner that amounts to a large circle of shift registers.The parallel method requLes a method of selecting the slavedwice so that only two devicesshare the data flow, while in the sedal loop scheme all of the data flows through all of the devices. In either method, multiple CPUs and slavedevices can exist on a SPI based network to shäre data. 157 t58 2.I I SERIAI COMMUNICATION USING I2C Interlntegrated C;rtub (I'?C) communication is a rystem developed by Philips Semicon ductor to provide communications between IC devices in enrertainment devices. It has grown to become a method to communicate with a multitude ofperipheral devices. I2C q,nchronous communication differs from SPI in two major ways:it is a "protocol-ed" lan, guäge (it requires a certain protocol), and it usesonly t!'o wires for communication. These are q?ic,Iy named S_)'ll.rru nout Ckcr (SCL\ nd Sycl)nno*' Data (SDA).Using only tlvo wres doesrlot allow data to flow simultaneouslyfrom master to slaveand from slaveto master asin SPI. I2C is sequentialin that data flows 6ßt ftom the master to the slaveand then (after the master-to-slave communication is complete) ftom the slal'€ ro the master ifneeded. Data only flows back to the master when the slaveis responding with data to ä master'srequest. Refer to Figure 2-48 and Figure 2-54 to comparethe SPI and I2C schemes.Figure 2-54 sho*s the clock flowing one way (master to slawe)and the data fowing both ways on a single wire. Figure 2-54 I2CDstoHow Using a protocol-based communication schemeis an er{cell€ntplace to usebuilt-in libranes. Developing the code to implement the protocol is often very time-consuming and a waste of time ifthe libraies exist. Figure 2-55 shows the hardware for an I2C example s1,stem.The s'stem is composed of an ATMega128 processorand a PCF3563 real time dock (RTC) device.The two components communicate using I'C. The software looks to be very simple at frst glance. However, the protocol is buried in the i2c.h andp(85 63.b \btal]es. These libraries are used lry pmng $e #includeEne in the code to indude the libraries. As a new programmer, you should open the 2e, header 6le and look at the function calls listed there. This will tell you how to call and use the librarv functions. Likewise, inspecting the pc{8563-h file will'allow you to see*har calls are pio"ided and what data must be passedto and what data may be expected to be rerurned hom the library tunctions. The software in Figure 2-56 shous the methods used to poll the secondsregister in the RTC. The secondsare then displayed on LEDs attached to PORT B. Maiz) ini,nalizes The Atmel RISC Processors ^ z Figure 2-55 _d 6 (dNrnPa o34N'rqPE6 (ocacn|.rl9PE5 (ceM4PE4 (@34/ArN1)PE3 (rc(o,aM)PE2 (Po/PmjpEl lRxDPoI)PE0 lzc ReolTimeClockExomple # i n n l r r r i p < n e o a 12 8 . h > /* I2C Bus functions*/ Fasm . equ __i2c-port=0x12 ; PORTD t =1 . equ --sda-bi . equ -scl-bit=0 #endasm <i2c. h> +include /* PCF8563 Real Time Clock functions*/ <pcfB563.h> #include void nain (void) t to hold time*/ / *variables unsigned char hour, minuLe, second; output*/ DDRB=oxFF; /*al1 usi-ng library*/ /* r2c Bus initialization i 2c_ini t ( ) ; Figure 2-56 I2CRealTimeClockSoftworeExomple(Continues) t59 t60 /* PcF8563 Real Time clock iniEialization lrc iniL { 1, RTC_CLkOUT OFF, RTC_TII'iER OFF); Fhile usins library call*/ (1) { /*!ead the currenE tine usids library .tc get rine {&hour, &üinure. &second) ; P O R T B= - s e c o n a l ; /'display secondsa/ ); funcrions*/ ] Figure 2-56 l'zCReolTine Clo.k sottworc ExaIlple (Continued) the ports, the I'zC bus (vi^ alilrtuty czJlto ;2t ;niil/), and the RIC via a c ) to rtc_ini11. The RTC tirne is then read via a call to rtcaet timeQ. Only the secondsare actually used, but the function from the library returns hours, minutes, and seconds,and so all must be stor€d el€n if they arc not used. 2.I2 T}IE AVR RISC ASSEMBLY INSTRUCTION SET LANGUAGE The C programming language is defned as a high-level language.A highJevel language rs one that is easyfor humans to read and allows complex operations to be performed in a single line of code.Microcontrollen, on the other hand, can actually only executewhat is called machine code. Machiae code consists solely ofnumben ald is a.v'erylow level language. Assembly language is very close to rnachine code in that it translates very direcdy into machine code. Assembly language is also considered to be a lowlevel language becauseir is r"ery dose to machine language. C languagecompilers won<by con?;ling iE Ct^nguage sratementsinto the assemblycode, which is then a:senbledinto machine code.The compilers accomplish this through the use of libraries containing assemblylanguage functions that implement the C language state ments. The C lmguage compiler looks at the C language statements and selectsthose li brary functions that implement the statements, compiling them into arr assemblylanguagc program. Finally, the C language compiler usesan assemblerro convert the assemblylanglage to machine code. There are actually two additional steps buried in the compiling and assembLingprocess: linking and locating. Zizlizg is the processofintegating libmry functions and other code into the program being comfned. Loeating ß drc processofassigning actual code memory addressesto each ofthe executableinstructiors. CodeVisionÄVR adds a funher step in that it converts the executablemachine code to än Intel formatted HEX file for do*rJoading into an AVR microcontroller using a clup Th.ltnel R I S CP r o . e t t ü s *1.61 Figure 2 57 shows this processusing one line of code from the ADC Example Software (refer to Figure 2-44). The diagram in Figure 2-57 should make the processrelatively dear, with two exceptions.The f,rst is that, asyou will recall, the program memory spacesare 16 bits wide and the memory addressesshovm under step 3 are the word addressesfor each instruction word. (Notice that each instruction shown is contained in a single word, which is appropriate in a RISC processor.)The program words, however, are split into b)'tes in the Intel HEX code line and, as a result, the addressesshown are two times the addressshown STBP 1 if r'lrit6 th€ (adc data c codle: >(3*1023)/5) LEDS = red; //roo STEP 2 conpile: to conpile The compaler uses iEs Lib.aries were adaled Lo the assembLy code (coments : Lhor fo! clarity) LDI LDI CP R30,Lo!'r(614) R31,HIGH(614) R30,R15 cPc R31,R17 BRSH 0x2 LDI R3O,LO!r(3) OüT 0x15,R30 hiqh {>3v) Lhe C coale into code by assenbly followinq the au into R30 the 1ow byte of the constant ;put R31 inlo ;put the hiqh byie of tshe consiant adc data low bvte the 1ow byte witb ;conpare in R16) ; (nust be stored carrv) Lhe hiqh bytes {with ;nos conpare 'e1se' t h e s r a lement i f u n l r u e t s o ,branch the red LED hrue, toad the value Lo lighr ,if ; inlo Rlo d I/o the value !o the port ;and ourput ;register STEP 3 As6enible: the nachine code The assembLer produces hand colunn is the code nenory The teft nord fron the cencer colum insrluction are shown fo! claritsy. instlucEions 000052 000053 000054 000055 000056 000057 000058 LDI R30,LoIt(61,, tDI R31,HIGH(614) R30.R16 CP R31,R1? cPc BRSH 0x2 LDI R30,Lor.r(3) ouT 0x15,R30 e6e6 e0f2 17e0 07fl f418 e0e3 bbe5 STEP 4 co4ve!! This Line rntel EEx for alonloaatiag! to rEtel HEx code contains Lhe machine I 100 0A2 0 0 1 5B1E!E5!ZEqqqLfnLQla84!4!E0E5!!8c Figur€ 2-57 in the center colum shom hold the address that will lanquage anal Lhe asserbly Conpilif,gP.ocess coate (see underlined t62 t Data Bres Tlpe Code Addr*s ofFisr Dala Blre Nunbs ofDala Bytesin üe Line htd HEX Line Stur Char.cter N,k: StM add..tb tberi,,Iar./b;rj Figure 2-58 lntelHEX CodeFomst under step 3 (2. Ox52 = OxAa). Figure 2-58 shows the format ofa line oflntel HEX code to assistyou in reading the line. The second apparnt difference betwecn the code in steps 2 and 3 is thar th€ order ofthe bytes appearsto be different. This occurs becauseunder step 3, the words are shown with the most signiEcant blte to the left, as is apprcpriate when witing numbers, but in the Intel HEX 6le, the nost signifcant byre is to t}re right, becauseit residesin the higher memory location. The Intel HEX format (refer to Figure 2 58) requires that each line begin with a ":'' to denote the beginning of a line ofhex code.Thb is followed by a byte that indicates the number ofdata bltes contained in a line. (Remember that the numben are in hexadecimat.so a "1O" meansthere are actually 16 dara blres on the line.) The nc.t two bl,tes are the address ofthe lirst data byte in the line---ubsequent data bytes are placed in subsequentaddresses. The tl?e code indicates the nature ofthe data in most older, smäller procesiors. tn the casc ofAVRs, the gpe code is actually used as a 64-Kbyte page indicadän, 0 for page 0. 1 for page 1, and so on, as is nece*sarywhen the code is destined for deviceswith large memory :prceswirh greaterthan Io-bitaddressingrequiremenrs. Finally, the.appropriate number of data bltes is induded, followed by a checksum used for error cnecKng. At this point, it may appearthat assemblycode is relatively hard to use,especiallywhen com pared to a high level language such as C, and is convoluted and obtuse. you are probably wondering why anyonewould be concemedwith the assemblycode.Assembly code is usefijl when a programmer needsto do operations directly on the registersofthe rrucroprocessoror when the programmer needsto very critically conrol the speedofexecution. Examplesofthe former would be writing adrrnced programs such as reat üne a?ent;ng:lstens (RTOS) ot other programs that must manipulate the microcontroller memory dleidy in order to operate. Likewise, it is usefirl as a debupging tool. Ermn in C programs often become apparent when the resultiog assemblycode is studied to determin€ what the processoris actually beurg told to do- fb? -4!nel RISC Ptaa"at t The second reason to use assemblycode is to very tighdy control the time of e{ecution. C language compilers use a library offunctions to implement the C lxnguage. Depending on the thoroughness of the compiler, there may be only a few Arnctions that attemPt to cover every instance, or there may be many Äfrctions that cover every pafticular instance of a programming command very ef6ciendy- Ifthere are only a few lirnctions that cover all situations, the chancesare very good that these functions use much nore execution time than is necessaryin order to cover all the scenario possibfities. In the caseofthe better C compLl ers, such as CodeVisionAVR, they have large libraries offunctions to cover most situations very efficiendy. In these cases,the need for assemblycode programming is reduced. Should the need for assemblylanguage programming arise, one relatrvely good way to handle it is to fißt \{rite the function in C and then, using the assemblycode files generated by the compiler, look at the assemblycode the compiler proposesto use for your function. You can then anallze the assemblycode by looking up each instruction in the function (refer to the inshrctions in Appendir G) and determine which ifany instructions are rcally not necessary Experience has shown that even well-optimized code can usually be speeded up somewhat by careful analysis of the assemblycode. 2.1 3 CHAPTER SUI.IMARY This chapter has provided you with the basic hardware background necessaryto choose and apply a member of the A\rR RISC microcontroller family produced by Atmel. Speci6ca11y, the architecture ofthe microcontrollers, including their memory system design and internal worhngs, hasbeen presented.Each ofthe usual peripheral deviceshas been de scribed, its use discussed,and an example presented showing how to use the peripheral. Should you encounter other peripherals not specfically mvered in this chapter, their use should be reaüly understood becausethey all work very similaiy. As a student, you should now be ready to meet eacn of the o\ectives of this chapter Chapter 2 Example Proiect: Part E This is the summary ofthe Chapter 2 example presented in pieces throughout the chapter. The complete program is as follows: -h> +inc tude <meqra163 + i n ct u d e < s t d i o . h > d- ä s-r e lpnt120l, .u-nF o dä ä s.-.' to t_pcl /'recordeal'/ to hold 120 sets of*/ s_rpnl120l; /tarrays / * daLa* / cnr.; currenr_e_.pn, /'rounfe! cufenr s rpn; /'va!iables / rcurrent to hold* vaLues*/ / r63 t64 u4slgned inr previous shaft capture rime; /*saved /* Exlelnal Interrupt 0 service routine*/ anterrupt IExT INToI woid ext into_isr(woid) { unsisned ioE current_captsure period; tine, = TCNTI; current captDre_tsine /rqer /'check for.o11 over*/ (curlent if capture_tine > prewious = current period capture_tine previous shaft-capture tine; culrent previous Eime fron /*cutenr /*periöd*/ Tinerl shaft previous*/ tine and*/ tine*/ capture_rime) = oXFFFF period current capture tsime + prewious shaft_capEure tlne; s rpn : (unsigned lonq)6086 / (unsisned lonq)period; shaft capture hine = currenc caprure_rine, /*save /'n-x! ca1 ula for*, o L/ ) /* External Intelrupt l service routinei/ interrupt IEXI'-INT1] woid exE inrl isr{voial) I - 0; data set_cnt. /-ctear counter to sEart /iq1oba1 /* Tiner rnterrüpt wariable 0 overflow interrupt service ITIMo OvF] void tinero ovf TCNTo = 6; /*reload (time cntr++:= if 500) for nunber counting*/ of Tine! 09*/ rourine;/ isr(void) tiner 0 for next pe!iod*/ fo! one second, increnent /*check counrer,/ { if (data ser_cntr e rpnldatä-seE < 120) cnLil s rpmldata_seE-cnt.l templdata set_cntsr++l /*record dara if = currenl e rpn' = currenE s rpn; = currenr_Eemp; less Ehan 120 sers+/ /.recolal*/ /'enqine rpn*/ /'iecord*/ / *shafE rpn*/ /*recard,/ renpi/ / 'englne I /'reset counter for nexL one second interval*/ Tle Atne/ unsigned previous_capture_tine; inr Inr e--üpt trrflr /+saved tine RISC Ptuestatt previousi/ fron '_ ^'rii^L service ^ --"v' touLi.erl i AFrl volo rlnerr_cäpr_rsrrworo, t'.n--6rrt'ä,i/ /*petiod* / = (256t lcR1H) + ICR1L; cufent caprure rine /*geL captured f o r r o l t o w e r r / /*check jt rimel peliod cdplu e-Limc 'previous.äpturF \-u!!enl - prewious capture time; current-caplure_tine rimei/ = oXFFFF - cufent + previous_capture_Line; capture tine : (ünsiqned lotg)).20E6 current_e_rpn / previous_caotu'e_L Lnsisned ima long)pFriod; f o r n e x t c a l c u lation*/ cuiient capture Lime; /tsawe period ) interrupt [aDc sFrvi.e INT] voial rouf ine' / adc isr(woid] { unsigned inr ADc DATA; a D C _ D A T A= a D c w ; /*qet alata fron ADC results reqister*/ p - r ( I o n g ) I 5 0 ' ( . l o n q ) a D C _ D A T A ) (/ - o n s ) 1 0 2 3 (1ons)100; J void nain (void) { Po!rs inirializaEionr/ pul1 up on bit /*enable 0 for upload switch*/ PORTB=0x00; DDRB=0x00; P O R T C - 0 x00; DDRC=0x00; /tenable putl ups on Port DDRD=0x0; / / * T i m e ! / C o u n E e r 0 ini!ializationl TCCRo=0x03; / *clock set Lo clk/64,/ TCNT0=0x00; / *starL tinero at 0*/ / * Timer/Counier TCCRlA-0x00; l initializatlon* / D, BiEs 2,3, & 6*/ r65 t66 TCCRlB=0x02; TCNTlH=0x00; TCNTlL=0x00; /'pLes..1e. 8, capture on tä 9 edqe. (s) initiatizationt/ htelrupt /' bo'h exLpr.ol inrerr.pt s erdbtect-, /* set both for falling edge rriqqered*/ the inle.lupL /t clear ftags in case rhey /'e.tanh1y sett/ /* External -I\rsv aaro; MCUCR=0:04; elFR=oaco; a.e*/ /* Tiner(s)/counter(s) InEelrupt(s) inirializarion*/ TIMSI(=0x21; /* tinero ove!f1ok, IcP iarerrupts enabLed*/ oaRT ini EializaLionj /' / UCSRB=0x18; /i enat,le transniEter / iselect 9600 baudr/ Analoq alisabled*/ /* Comparator and receiwelr/ sFIoR=0x00; /* ADc initializaEion* / ADMUx=ox3; channel /*select 3 and AREF pin as rhe referenceN/ /*woltaqre inputa/ ÄDCSR=0xE9; /*enable aDC, free run, sra!!ed, clock prescale! of /* cLobal enabte inLerruptst/ { if (lPINA,0) /*noEe: ssitch nust /* is all sent* / be reteased before dara*/ { unsisned cha. x; /ttenporary counter /!pr rnr .o unn ril tcs in rhe ri.st printf ("gs , gs , gs \n", Enqine 'Shaft RPl4", "Tenperature" ); (x = 0; x < 120, x++) for variabLet/ sprF-ds Rptr", eec lor- { /* prin! one set of datsa inLo one line on r:he*/ / *spreadsheeE'/ gd, p.intf ('gd, Ed \n",e_rpntxl, s rpmtxl , Eenptxl ) , J l 64*/ The Atnel RISC Pra.ssar! In summary,this program is but one way to accomplish the task; there are maoy others that would work equally well. And there are some enhancementsthat would improve slstem oPeration. Some ofthe more likely rariations and enhancementsäre Iisted here: . Store the rpm andt€mperaturedataäs raw data,not conveftedto rPm or temPeraEachPiece ture.Inthisway,time wouldbe sävedduringeachpammetermeasuremenl datä to the PC in the routine that sends th€ of raw datawould needto be converted asthe darais sent, ' The rpm meäsurements couldhavebeenacquiredby actuallycountingthe pulsesfor by 60 to 8et rpm.In this cäs€.th€ | -secondroutinewould I secondandmultiplying and clear it for the next l-secondcounr recordthe count . Ther€ is no protection to preventbümpingthe start switch after data is r€cord€d and beforeit is tmnsferredto the rc. Datacouldbe lost in thisway.One choicemiShtbe to disallowfurtherrecordinguntildatais sentto the PC.Theproblemwith thisis that if th€ driver stans the r€cordingprocessinadvertently,he hasno wäy to recoverand ' transferthe right data. Anoüer choice miShtbe to provide a"data lock to88l€ switch.With this switch set one way,datacould still be recordedwhenev€rth€ start switch is pressed.Setting$is switch to th€ other positionaft€r the good data h recordedwouldprev€ntfurtherrecordinguntilthe datahadbeensävedto th€ PC. There are many more variations and enhancementspossible- Häving completed this chapter. vou should be able to add severalvoursell 2.t4 EXERCISES (S€ction2.3) anda microcomputer | . Explainthe differences betweena microcontroller *2. Des€ribethe followingmemorytypesanddelineate th€ir uses(Section2.4): A. FLASHCodememo.v B. Datamemory memor), C. EEPROM 3. Explainwhya sectionof datamemoryis calledl/O (Section2.4). stdck(Section2.4). 4. Explainthe funcdonandpurposeofthe processor 5. Explainhow an interruptfinds'ts wayto the interruptserviceroutineto ex€cuteit 2.5). whenthe interruptoccurs(Section *6. Write a frqment of C language codeto initializeExternalInterruPtI to a€tivateon a falling€dgeappliedto the externalinterruptpin (Section2.5). 7. What is a watchdogtimer andwhy is it used(Section2.5)? *8. Write a fragmentof C lantuatecod€to initialize the Port C pinsso that the upper nibblecanbe usedfor inputändthe lowernibblecanbe usedfor outPut(Section2 6). t67 t68 9. Write a fragmentofC code to initializePonA and set the leastsignificantbit of Pon B to be input,and the balanceof Pon B to be output (Sedion 2.6). | 0. Name änd describ€at leasttwo distinctlydifferentfunctionsthat can be performed by ä tim€r/counter {Section2.7). + | | . Sketch the waveform appearing at the output of the USART when it tränsmits an "H " at 9600 baud (Section2.8).Thesketch should show voltagelevelsand the bit dura" tions,in additior to the waveform' | 2. Sketch the waveform appearing at the output of the USART when it transmits an "F at 1200baud (Section2.8).Thesketchshould show voltagelevelsand the bit durations. in add:tionto the waveform. * 13. Compute the missing\.aluesto completethe followingtable relatingto analogto digitalconversion(S€ction2.9): Dighol Out 4.2V 10\. 8 1.6V 5V 10 5V L23 10 t0v 223 I 14.Describethe differences betw€enthe USARTandthe SPIserialcommunication fsections2.8and2.l0l. t 5 . Detailthe stepsin th€ compilingprocess(Section2.I l). ""'" preceding an cxeicise number indicates that the question is answered or partiälly answeredin the appendix. 2.I 5 LABORATORY ACTIVITIES I - Createa proSramthatwill turn on an LEDwh€na fallingedSeoccurson external interrupt0 andwillturn it off whena rising€dgeoccurson externalinterruptL 2. Createa programthatwill demonstmte how a watchdogtimer resetsthe processorif the proSramhangsin an infiniteloop. 3. Createa programthat will r€adthe datäon all€ightbitsof PonA, swapthe nibblesof that data,andoutput the result to Port B. 4. Cr€atea simulat€d enginespeedmonitorthat will li8hta yellowLEDif the motor 'tpeed" (aTTll€vel squar€wave)dropsbelow2000Haa red LEDif the speed exceeds 4000Hz,anda SreenLEDwhenthe speedis betweenthesetwo limits. Tle,4tnel RISC Prateßals 5. Createa programto vary the spe€dof a smallmotor (or the brightn€ssof an LED)in sixteenstepsfrom füll ofi to tull on usingPWM control. Control the speedor briShtnessthrouShloSiclevelsappliedto tie lower nibbleof PonA Create a proSrämto output the ASCIIcharacter'G" every 50 millisecondsthrough the USARTat 9600 baud.Obs€rveboth dteTTL-levelsiSnalon the microcontrollert TXD line andth€ RS-232signalat the output of fie mediadriver usingän oscilloscope.On each\ /aveform.identifythe start bit, the stop bit, andthe databits of the transm!ft€dsiSnal,asw€ll asthe voltagelev€lsof the waveform. 7. lYodit the proSrämin AclMty 6 so that the'G" is alsotransmitt€dfrom th€ SPIbus. to displayboththe transmittedSPlsignaland the SPIclockand Usethe oscilloscope identit th€ dätabits. Use the analog-to-diSital converterto createa simplevohneter that m€asur€svoltag€ in the rangeof0 to 5V to an accuraq/of0.lV Displaythe r€sultseith€ron the terminalusingserialcommuni@tion oron a port wherethe uppernibblewouldbe the volts digit and the lower nibblewould be the tenths of volts di8it. t69 Standard l/O and Preprocessor Functions 3.t oBIECT|VES At the conclusion ofthis chapter, you should be able to: . Use standardI/O functionsto yield datafrom your programsfor informational purposes aswell asdebugging . Redefinethe ba5icl/O operationsso that the srändardI/O functionscanwork with peripheralsotier tian a USART . Usethe standardinput functionsto r€ad user datainto your progräms . Understand the üseof standardoutputformattingto simpliryprogramcodinS andget professional-looking results . Use the #define stat€mentto d€clareconstantsaswelt as redefinefunctions . Use the #include statem€ntto bring informationinto your programfrom . Userhe#pragmä statement your programduring to optimiz€or customize the comDilation Drocess 3.2 INTRODUCTION The standardC languageinput/ouput (yO) frrnctions are a method of sending These information to and gining information from your program as it e"vecutes. functionsarebuilt from simple characterinput and output functionsthat are easily tailored to meet systemhardwarerequircments.Someofthe higher{evel tunctions associated with the standardC languageVO indude the ability to format numeric and text output, aswell asprocessand storenumericor tert datainput. The standardC languageI/O functionsoudinedherewereadaptedto work on emThe protogpes for thesefunctions beddedmicrocontrollerswith limited resources. t7l t72 can be found in the stdio.h file. This file must be brought into the C source code using the #indude preprocessorcomnand before the functions can be used. Preprocessorcommands are used to add readability and apand rhe ftnctionality of your progran. These commands include #def,ne, #includs and #pragma, aswell as other conditional commands such as #ifde{, #else, and #endif These commands are used to quide the compiler and provide information about the progam bdore jr is actualy compiled. Preprocessorcommands are also used to make a program more portable (capable ofbeing moved to another hardware pladorm). The preprocessorallows a programmer to provide more detail in the definition and construction ofa program. 3.3 CHARACTER INPUTTOUTPtT FUNCTIONS - gefcrraro A}||D putchar() At the lowest level, the input/output functions are getcl)ar) ?.r,d? tcha()'f\ese fuoctions provide a method ofgetting a single charaaer into a program or sending a single character out. These functioß ,re gen€rally associatedwith the mtuersal sychronousand aslnchranaß me;ret-tran:mitter (UMRO or serial communication pon of the microcontroller The higher-level standard C language VO functions use tlese iprimitives" as a baseline for therr oPeration. This al1owsa programmer to easily change the data input and oueut sourcere quirements for an entire program by sirnply attering these two functions. The standard form of thesefunctionsis asfollows: char qeEchat (void) ; // // returns a characrer by the usÄRT, usinq void putchar c); // // trdnsmirs l\e.hd tshe USART, using (char received polling. u r-g dc.et po1linq. Tlpically in an embedded system, prior to using these 'stocld functions, you must do the lollowing: . Initializethe USARTbaudrate. . Enablethe USARTtransm'tter. . Enablethe USARTreceiven For example,in the code below, the program initializes the USART and then sits in a while Ioop. While in this loop , t\e progr€rrLcallsgatha4'l to wait for a character to be received. Once a character is received, it is echoed back by ca]Jingthe ?atchar) tuncrion *include #include <nesa8515. h> /* include <stdio.h> /* include +define xrat 4000000L +define baud 9600 processor specifie Etle standard /i qud,lz /* Baual c 1/O function .'vsrel r/ raEe */ infornation deflnitions f!6q.ar-, IUl */ Sta,dard I/O and Pr"prat.'tor Frnttia4 void nain(void) { /* initlatize the USÄRT's baud räte */ UBRRE=0; hitialize the USART control RX & TX enat'led, no intetupts, */ I data bits UCSRB=0x18; register /* rnitialize frane fornaL, I sFop bit, äsyn.hronous */ no parity /* I data ltrirs, opprä.ion änd UCSRC=0x86; while (1) k=setcha!O; ; Pulchar(k) /* /* .eceive rhe and echo iE characEer back r/ i/ J All the standardinput/ottpt fulrct]ors ve getcharqaÄ putehar). If pt tntendto useperipheralsother than the USART for standardinput/outpu! you must modlly the g*charX andpuxiar(.) turcnons aaordingly.The sourcecodefor thesefunctionsis usuallylocatedin the stdio.hfle. Here is a gpical rersion otgetd)a/) arrd7 tcba/) for anAVR microcontrollerasyou might 6nd in the stdio.hfile: chai getchar {vold) { while((ucsRA & Rxc)==o) // // wa\r for characle! teLtr^ the characLer !o entser USART to the caller J void putcha. (char c) { while({UCSRA oDR J ; ci & UDRE)==0) // saiE for tlansni! / / !o be enptsY.. | / put c out to (he USAPT resister lT3 t74 'lhe gettba| and?utehar) tunctions can be replacedby customized tunctions that use a different USART a serial peripheral interface (SH), or a parallel port. Wher gexbar| rs cal1edin the example above,it forc€s the microcontroller to wait until a character is receivedbeforc alowing the program to go on. In some applicarions, it may not be desnable to sit arrd wait for a character to arrive. Instead, interupts can be used to allow serial communication to be handled in the background while the main program continues to run. Interupt-driwn serial communication allow chanctcrs to be placed in a buffer or queue as they come in, in the background. Then, when the main program is ready for the received characters,it reads the charactersftom the buffer and processesthem. The sameis mre for transmitting charactcrs.To prevent waiting for a character to leave the serial port, interupt driven transmitting can be used.As the transmit register of a USART empties, it cnn genente a.rlinterrupt that allou.s the next chancter from a transmit buffer to be sent. This processwould repeat for as long as there were charactersin the buffer. In the example below, gerrlar) nd, paxhar1 placr charactersin, aad get characters from, the Rl{_Bufb rnd Tr. Bufer chzr^ctet mays, respectively.In this case,the &etctar) and Puxl)ar) tuncao s a d,then support might look like this: #include +define +defiae <megaa515,h> xral 4000000L baud 9600 /* /t quarEz crysLal Baud race */ frequency IHzl */ // USART Receiver buffer +define Rx BUFFER srzE 24 (buffer) char R.--BufferlRx BUFFER SrZE+11; afay // charactet char Rx_r'ir_Index; rhe buffer / / j,\dex of next char tso be pui into chai Rx_Rd_Index; of next char ro be feLehed fron //index rhe buffer char Rx_countser; total count of characrers //a in the buffer bit Rx_Buffer-Overftor; // This flaq is seL on USART Receiver // buffer overflos // USART Transnits buffer +dEfiNE TX BUFFER SIZE 24 char Tx Buffer (buffer) [Tx BUFFER sIzE+1]; // .,raracter atay char Tx_Rd_Index; of next char ro be pur inLo rhe buffer //inalex char Tx_Wr_Index; of next char to be ferched //inale: fron the buffer chai Tx_counler; toLal count of characters //a in Lhe buffer bit fPrinedlr; is used !o sLar! // chis flag rhe iransnir --p l // incFrrupls, bhpn the but!-r 1s no o.ginterrupt // USART Recelver interrupt IUSART Rxcl void t serwice usarr rx rou.lne isr(void) Stradad I/O ald Pe?roesar F,nttiont Rx_Buffei if = c; lRx_Wr_Ildexl (++Rx_Wr_Index Rx_wr_Index put /* > RX SUFFER SIZE) = 0; receiveal /* wrap char the in buffe. pointer */ i/ /* keep a character counE r/ */ check.. / * overftow = RX_BUFFER_SIZE; RX Counter roo nany chars cane */ /* if = l; Rx Buffer_overflow they could be used */ /, in before r rhat */ could cause an edorlr (++Rx_counter if \ > RX_BVFFER sIzE) t // Cel a chalacter cha! qe!cha! (void) fron the USAiT Recelver whi Ie (Rx-counter == 0) /t wait c - Rd Indcxl, /, set Rx BuffertRx if (++Rx_Rd_hdex if (RX_Counter) Rx_Counler > Rx BUFFER srzE) i /. /* ttuffer for one from w.ap keep ä .ounl */ a characre!... rhe the buIIel pointer (burre' si-e) ,,' */ ' ) interlupt / / U S A R TT r a n s n i t t e r service loutine intetupt I U S A R T _ T X C lv o i d u s a . r t x i s r ( v o i d ) if{Tx_Counter != 0) I == 1) if ( fPrineallt I = 0; fPlinedlt if(++.Ix Rd_halex / * only send a char if one in buffer /* traDsnission, then don't send the /r Lest and wrap Ehe poince! > TX_BUFFER SIZE) */ */ 175 176 = 0, TX_Ral Index Tx_Counter keep track ; /* of */ the counter J if (Tx_Counter != 0) t UDR = Tx_BufterlTx /* Rd Inalexl; othe.wise, */ send char our port änd drdo rhe poinfe! /'tFsf i f ( + + T x R d _ r n d e x > T X B U F F E RS r Z E ) Tx_Rd_Inalex = 0; 'IX Coünter- ; /i keep track /t clear */ of the couDler j ) U c s R Al = 0 x 4 O ; tx inte.rupt */ flas ) // wtiLe a characte! to the USART Tlansnitter L'uffer { = 0; char stuffiE whi 1e (Tx_Counter /' i if(Tx > (Tx BUFFER_SIZE 1)) WAIT! ! Buffer is setEiDq =counter = 1; sruffit O) /* If buffer Tx BufferlTx_brr_lodex++l=c; tf(Tx enptsy, jd /+ the keep /* track ! serup char > I'X_BSFFER sIzE) rdr halex TX W! Inaiex = 0; /* futt! of */ for inrerrupr */ */ in the buffer.. vrap the poinLer buffered chars */ 1X Countei++, if (stuffit == 1) I UDR - ] cj /' ato ve /r rhis hawe to char "Prine srdlrs Ehe punp'? I he TiX inLe */ ,upEs,, r */ Stand't.l I/O asd Pr.?tu.üsor . // Ftnctiaht -hese Lel I lhe .odpiler to raplacF tne srdio,h de.inäs anal putcharO sith ours.. version of getcharO That Nay, att the other stdio,h functions can use Ehen!! // +define _ALTERNATE GETCIIAR +detine _ALTERNATE PUTCHAR // ô\i, // replacenents *include we include the library anal it will understand our <sldio.h> I the usaRT's // iDilialize UBRRH=0; UBRRL=Xra1/16llraud-1,. // rniEialize // Rx & Tx enabfed, / RX a TX inLerrupLs baüal iate Ehe ssART cooElo1 reqister: enabled, 8 dara biEs // UCSRB=0xD8; // I4ilialize // ! stop bit, aa paraLy fomat, I alata blts. the frane asynchronous operation and / / UCSRC=0x86; Globar // +asn("sei") intedupt enat'le { if (Rx_counter) t // \ - sel.hä.O; Putcha.(k); are there any received characters?? // ger // and the chalacre! echo it back ) // // since olher there things is no waitinq on qetchar can be done!! or putchar-. 177 t78 In this example,the variable RX_Coanter contuns the number ofcharacters that hal.€ been placed in the receiver charzcter atny RX Bufer by the interrupt routine. Tlis prevents the program ftom callinggerr/arlJ and then sitting idle until a new characterarive s. Rx_Counter is tested in each passofthe wfiile loop- Ifit is not zero, then chrracters exist in tne Rx_Burftr characterarray and a call to getrlar) vÄ rctrßve a,draracter without hesitation. Since?uxfiar) ß lr'terntpt driren aswell, it adds älmost no time to the program execution. ?utcba pl^ces ^ chat cter in the hürsmit buffer and starts the transmit interrupts. From that point on, interupts move the charactex from the transmit buffer to the USART each time it becomesempty, until the transmit buffer is empty. Thenames' ai,'renratE GETCEÄR"and" ALTERNATE_PUrCILAR " areusedasa signal to the compiler to use the newly dedared getthar() ^nd ?"ttha4 ) tunctions, insread oithe ones provided in the stdio.h header file. 3.4 STANDARD OUTPUT FUNCTIONS The output tunctionsof a standardlibrary indude r1:,eptlLtstri"g, ?1tß0. print formafted, prinfl| tnd prrnt stlng fotmatted' sqn ü0, fitr'ctions.In the caseof an AVR microcontroller with its RAM änd FLASH memory areas,the additional tunction of put string FLASH, ot putsf), wasaddedto allow the printing of a constantstring locatedin FLASH 3.4.1 PUT STRINc-p!ti0 The standardfonn ofpztP is void puts(char rstr); This function usesTzrrla,., to output the nul terminated character string sr4 located in SRr\M, followed by a new line character ('rn). Thc pztl/ tunction is caled by the program, and a pointer to a string must be passedto it. The following example calls?uß0 to otlrp:ut the string "Hello" follo*rd by the new line character to the USART: #include +include <nega8515.h> i n.t ude p!o, -ssor /, <stdio.h> /* +define +define incfude Ehe standaid xral 4000000L baud 9600 char s l6l= void nain (void) "Hel1o"; /* initialize UBRRE=O; lhe sp^. i c I/o funcrion /' qLo.lz /i Baual rate /i declare a RAM based */ initialize it .r vs, -l t/ USART' s baud rale atef,nirions trpq.-n */ y srring and */ Sta,d6d UO.and.,Pre?rct4tü UBRRT=xta1 /16lbaud-1 ; hitialize the üSART control /t Rx & Tx enableal, no inteüuprs, */ 8 data bits Fnttiaü register UCSRB=0x18, Initialize frane fornat, 1 stop bit, asynchronous */ no pa.ity /* I data b'ils, operarion and UCSRC=0x86,. puts(s); prints // He110 followed by a newline character while (1) ] In the program above,"s", which is the addressof the aray "s i 1", is pzssed to the ? tsj function as a pointer to the array. 3.4.2 PUT STRING FlAsH-putsf0 The put FLASH (constant) string tunction has the standard form of This tunction uses2zraüa4'l to output the null-terminated character string rtr located in FLASH, followed by a new line character The following example ca11s2zrs/dto output the string "Hello", located in FI-ASH rnemory followed by the new line character to the USART: +include +include <nega8515.h> /r incrucle plocessor <stdio.h> /* #define +define flash void inctude Ltle stanalarat xtal 4000000L /* baud 9600 /* chax st6l= spec "He1lo ; ric C 1/O quarlz crysla1 Baual raEe */ /* in o'n- function /' IHz] a FLASH baseal string iE t/ iniEialize declare nain(void) the ' defniLions frequency t /* inirialize UBRRH=0; io- VSART's bäud rate Initialize the USART control RX & Tx enabled, no inteüuprs, * / d a r a b i t s 8 */ reqister "/ */ and W t80 UCSRB=0x14; Initiatize frane fomat, 1 stop bit, astmchronous */ no parity UCSRC=0x86; /* pulst(s); // prints Hetto followed by a line pursf('Hello"); // prinrs Eel1o fottowed by a line-feed vhile feed (1) ] 3.4.3 PRfNT FORI'IATTED-Pii0 fo The print formatted firnction has the standard form of void pllntf(char flash tfnEsEr L atga, ars2, ...1)i This function ouputs fotlr1atted text, nsntAllntelia4), according to the fomat specilication iir the constant süingPatr The format specification stinEfntstr 1sz corrstantstring and must be located in FLASH program memory;fizr't is processedby thelrintfl) rcüon. fnxtr can be made rp of constant charactersto be output direcdy aswell as by special for mat corrmands or specifrcÄons. As printf) is processingtheJ6z6r4 it outputs the charac ters and expandseach argument according to the format specfications that may be embed ded within the string. A percent sign (%) is used to indicate the beginning of a format specif,cation. Each format specification is then related to nn argument, a/g1, arg2, ^rd so on, in sequenc€.There should al*zys be an argument for each fomar specification and uce The described impleme t^non of drc prinfl) format specifcations is a reduced version of the standard C funaion. This is done to meet the minimum rcquirements of an embedded syttem. A firl1 ANSI-C implementation would requirc a large amount of memory space, which in most caseswould make the Arnctions uselessin an embedded application. Table 3-1 shows the format specifcations arailable in the CodeVisionAVR library. When the format specilications arc used, there are some rules and modiAers that apply: . All numericmluesare rightalignedandleft paddedwith spaces. . lf a 0 (zero) characteri! inse.ted b€tweenthe % and d, i, u, x, or X, then the number willbe lelt paddedwith 0s. . lf a "-" (minus) characreris insened betw€entl|e % and d, i, u, )q or X, th€n the numberwjll be left align€d. Sta"dard AO ßnd Pre?ra.ertar Ftflttiant . A width sp€cificationbetween I and 9 cänbe insert€d betweenthe % and d, i, u, x, or X to specifythe minimumwidth of the displayednumb€r. . Th€ format string sp€cmcationsare usedto tell the prtnfo funcrion how manyargumentsto Process. outputs rhe next aigrnmt ß m ASCII chmcter %d outputs rhe nqt dgtnent ß a decimal integd %i outPuß üc nctr aigm€nt ß , d.ciDrl inEgd outputsthe next argumcnta o uigned deimr i.teger outputstne next argumentG u unsignedhqadeim,r int%d usins lmrcase letteß 9{X outputs th€ nert aBunent ß u unsigned hdadeimal outpüts $e next dgment 6 a null teminated chmctd intege using ulpercas letteß string, located in SRÄM outputs dE % cnmctd Table 3-l printf formot Sp€cifcotions Here are some examples ofhow the format specifrcations a$ect the output. Pipe marlß (l) are used to help clarify the effect ofthe formatting by showingwhere the beginning and end of the text and white spaceare located. They are ôt rcWreÄby the printf) tunction: i\t i = 7234; cha! p l10l = "t{eIlo'; g5dl",i); printf(" prinEf(" prinEf(" lg-5dl',i) lg05dl",i) t i prinEf("lgo4xl",i) t printf("18s:s04xl',p,1)r // // // // // // // r 2 34 1 woutal p.int: woutalprint: woutalprint: {ou1al prinl: woulal print: woü1d print: roü1d print: t234 1234 01234 4d2l l04D2l lHe110:04D2 Here is a programthat usesqrintJO to prit a string and an integer valuefrom the same +incLude <meqa8515,h> +include incluclp /' <stdio.h> /i include processor lhe sEandardl +defioe xtal 4000000L /t #define baud 9600 /+ void nain(void) quariz soecif C I/O crystal */ Baud rate . inro function -o :on { */ defnitions frequency [Hz] */ l8l t82 inl-iälize /' UBRRI{=0; .he USART's bducl raLe UBRRL=xra1/16lbaud 1; hitialize /* t h e U S A R Tc o n t r o t r e g i s t e r Rx & Tx enableal, no interrupts, a data L'its t/ UCSRB=0x18,. hitiatize frane fornaE, 8 data bits, 1 stop t'it, asynchroDous operarion and */ no pariry UCSRC=0x46,' /* for (T=0; { I<100, I++) // pri\E a fornatted strins and rel1 printf("princf exanple, I = 8d\a",I); abour I ) while(1) Running this program would re$it irl the text string:printfexample, I = " being printed 100 times. Each time, the number 0 to 99 would be printed following the string Note that the '*a indicating where the number l should appear,as ,fzztrlr contains all the text, plus the well as the end ofline character ('td). That one statement does a 1ot ofwork!! You shonld be aware of the costs associatedwith 6e useof pr;nrf0.'lhe pnntrl tunction is doing a great deal ofwo* and therefore needscode spaceto do so.Using the pr;nf) funclon adds flexible, powerfrrl, formaned outpuq without mary lines of code being gped. Hovrever, t\e standad.llbraq prinfl) firnction itself contains ser"eralhrmdred lines of assemblycode that are automatically added to your program in order to stpport pinf). Once the frracuon has been added to the code,each call to the function adds but a few lines ofassembly. 3.4.4 STRING PRINT FORMATTED-lprrn.f0 The string print formatted function has the standard form of void sprintt(char *s!!, char flash tfnEstr t argl, , atg2, --.1); The operationofthis tu nctor'ß rderLncatrrc prinf) exceptthat the formaftedtext is placed in the null-terminatedcharacterstring rrrinstead of ctJhng? tchar). For e.rample: +rnclude <neqa8515-h> /' ir.lude processo! specilic ir o'a-.ion Shnda +include Fth.tiafls <stdio.h> /' xral baud +define +define AO and PreProrütor include 4000000L 9600 char st28l; vold main (woid) /* declare the /t /t standard c I/o function quartz crysral */ Baud rate a RAM based string Iitialize */ defnitions fre.ruency lHzl */ and */ lt I */ the üSART's baud rate /* initialize UBRRH=0; UBRRL=xta1 /16lbaud-1 ; ' I n i I ial : za fhp USART cont r ol no interrüI)ts, Rx & Tx enabled, */ I dara birs -q sLar UCSRB=0x18; /* hitialize frame fornat, ' srop biF, dsynchtonous */ no parihy I data opP'd biLs, ion ddd UCSRC=0x86; for (I=0; I r++) s wilh rhe fornatted // load lhe string exdpte, I = gd ,I); splinlf(s,'sprintf 's' ! ! puEs {s); // then print I<100; daLa ] while(1) J The execution of this program would result in the text sting "spintf example, I = " being printed 100 times.Each time, the number0 to 99 would be pdnted fo[owing the string Tn this example,the s?intf) function formatsthe ougut and placesit in a charactcraffay"s" insteadof sendingit our &ß USART nsinsPateharq.The 7ar(/ tunction then sendsthe string"s" out to the USAR'I uingthe 2uxhar) finction ard appendsthe new line character ('\n') to the endof the sting. 3.5 STANDARD INPUT FUNCTIONS The input functions of a standardlibrary include the get string, galsl), scanformatted, rfrt{r, and scanstring form*ted,, ssranf), fvrctions. Just as the root output tunction is ? tüar), the ßot tnptrt tunctio^ is geftlar). h d1czses,gexbarj is calledto gather the 183 tu necessarydata. So by changing the open(ron of getüa4), the data source can easily be altered. 3.5.1 GET STRING-gets(,} The standard form ofgetll char is rqers(char *s!!, unsisned char 1en); This function usesgrlrral, to input charactersinto the character string srr, which is terminated by the new line character.The new line character is replacedwith a null ('r o') by the gezs(/function. The maximun length ofthe sting is ln-If hn charzcterswere read without encountering the new line character,then the string is terminated with a null and the function ends.The function returns a poirt€r to Jt For example: +include <meqa8515.h> #include in..ucle /' <stdio,h> iaclude /t xtal baud +define +define 4000000L 9600 char sl12l; void nain (woid) /* declare pro.essor Lhe saandaral /* /* _rc spec c I/o quartz function crystat */ Baud rate a RAlt based string into!m..-on */ dennilions frequency IHz] */ */ { */ /* initiatize the USART's baud rate UBRRH=0; UBRRL=xrat/16lbaual 1; Inltiatize /* rhe USART conrlo1 register Rx & Tx enableal, no interlupts, i/ I dara birs UCSRB=0x18, /* Initiatize frane for@E, 1 stop bit, astmchroaous */ no parity 8 data bits, operation and UCSRC=0x86, whi 1e (1) t // !rets(s,1o); puis(s); // prints get a strinq s r'n9 's' from the standard input rolroded by " r i.e feed Stdnld,.t I/O and Pft?rat4tar Funttians In the program above, characters will be read from the stadard input, ten chancters at time, and then echoed to the standard oulput with a line feed appended. SCAN FO RMATTED-s<dnfo The scan formaacd function has the standard form of s q .d address, -.-n "-. ..-l); r.hd l"sh ,ttrr -fL l -s-. d!o "dd - q2 This function performs formafted text input, using getrbar), accorCnigto the format specis constant and must be incrtions in thc,fziv' string. The format specifcation stringltrr located in FLASH program memory. fnnction,rt 1Jt is proce$edby the scanJl tuncnon /zzsa can be made Just ^s ni $e Pinf) up ofconstant chrracters to be expectedin the input str€am, as well as special-format commands or specifications.As $ad(/ is processingthefur'la it inputs data using rhe getüar1 funcuon and either matches the rcceived chracter to the one found inr+*'r' or converts a se es of chaJactersfor each argument according to thc fomat specifications that may be embeddedwithin thePbt string. A percent sign (%) is used to indicate the beginning of a format specificatron. Each format specification is then related to an argument, arg1, arg2, and so on, in sequence.There should alwayr be an argument for each format speci6cation The arguments, argl, arg2, aÄ so on, xe the aAlressaf ot Paintersta v.dl^bles. (Not using an addressor a pointer as an agument in this tunction can lead to some very disappointing results!) The function returns the number of succcssfrl entries or -1 on error. The described implementation of scanf) form r specif,cations is a reduced version of the standard C function. This is done to meet the rninimum requirements ofan embedded s1stem. A firll ANSI C implcmentation would require a large amount ofmemory space,which in most caseswould make the tunctions uselessin an embedded application. Table 3 2 shows the format specifications available- inputs the rqa rgument as m ASCII chmcter inputs thc rqt argumcnt as a ddiml %i integer inputs the ne{t arguments a deimal i*eger i n p u F ' h e n e y t! A ! m c n , , . r n inputs the next argünot unrgn.d de.;rJ inregq d o unsigncd hsadecimal integer inputs the ndt atgunmt as. null tcminaed Table 3-2 s.onf-FomdI Spe.ifcdjons chracter string t85 t86 When the scan format specifications are used, there are some rules that apply: . The whit€ spacecharäcters,blank(spacE,andtab are ignored. . Ordinary characters(exc€pt{or %) are expectedto matchthe next norFwhite space characterfrom the inpur Here is an example that prompts the user for inputs, separatedby a comma, and then calls nanfl) to wztt for the iryut and store it into mdrble s. Fnally,pnnfi) is cdled to format and print the numbers back to the user: +include <nega8515.h> *include includp /' <stdio.h> /* include processor the +der,-e xLaI 4000000L /" +define baud 9600 /* void speciaic stddaral C I/O inlo!md.ion function qud, Lz crysrql t/ Baud rate ' */ de6nitions lrpqupn y hz ' nain(void) t */ /* initialize tshe USART,s baud .ate UBRRH=0; UBRRL=xtal/ 16lbaud 1; Initialize /* lhe USART control reslster Rx & Tx enabled, no inteffupts, r/ I alata bits UCSRB=0x18, /* IniLi-alize flde fornat, 1 stop bit, asynchronous t/ no parity a data bits, operation and UCSRc=0x86; two inteqers i, j : { .Enter scanf { " gaI,gx\n" , &i, &j } ; // sex tso inleqers, // anal one hexadecinal // separaEinq then pursf ptinrf{ while(1) gd, g04x',i,i); // pr-nL ; , ooe alecinaL with a coma Lhe va.lups ano.cop.. Frhrtions Staadard AO and P,e?,aüü.t 3.5.3 SCAN STRING FORMATTED-s5cdrf0 The scan string formatted function has the standard fonn of siqned chai sscanf (char *sLr, *fntstr char flash arql address, L arq2 address, ,,.l), This function is identiczl to vanfl) except thzt the formatted te".rtis read ftom the nullterminated character string ra located in SRAM. Modi{,ing the aboveexample to use$rarg(/ to get the data from a string instead offrom the standard input (the USAR'I ßing geteba,O Voduces the following: <nega8515.h> plo.essor . " in.luda <stdio.h> *include #include include /* xtal baud +define +define /* declare char s l14l void rhe sEandard 4000000L 9600 /' /t C I/o function definitions quartz crystal ]/ Baud rate a RAM ba6ed strins = {"1214,äbcd\n'}; and r/ informar ion spe.'.i. frequency initialize tHzl */ */ i!r/ main (woid) { inr i, i; /' initiatize the USART's baud '/ late üBRRL=xta1 /16lbaual-1 ; Initialize the USART concrol /* Rx & T'x enabled, */ I dara birs no register interrupts, UCSRB=0x18; /* hitiatize frane fornaE, 1 stop bit, asynchlonous */ no parity I data bits, operation and flon the t{ÄM st.ing // get Llre values sscanf (s, " gd, gx\n' , &i, &j ) ; one decinaL // geL Lio inteqers, // princf("Sd, and one g04x",i,j); hexaatecinal // print wiLh the 's' a coma values and slop.. lA7 t88 vhi 1e (1) 3.6 PREPROCESSOR DIRECTIVES Preprocessordirectives are not actually part ofthe C language ryntax, but they are accepted as such becauseoftheir use and familiarity. The preprocessoris a separatestep from the actr:al compilation ofa program and happensbefore the actual compilation begins. The most common directives arc #defne and #indude. The preprocessordirectives allow you to do the following: . Includetext from otherfiles,such asheaderfilescont ininglibmryanduserfun€tion PrototyPes. . Defin€ macrosthat reduceprogrammingeffon and improv€th€ legibilityof the sourcecode. . Setup cond;tional pur?oses compilation for debugSing andto improveprogram Dorräbilit . lssuecompiler-specific directives to generalize or optimizethe compiladon. 3.6.I THE #INCLUDE DIRECTIVE The #include directive can be used to indude another 6le in your source.There can be as many 1i1esincluded as needed,or as are allowed by the compiler, and includes can be nested (meaning that an included file can contain another, non-recu*ive, #include). Tlpically, there is a limit to the depth ofthe nesting, and the limit will wry {iom one compiler to another In the CodeVisionÄ\G. C Compiler a maximum ofsixteen nested flles are allowed. The standad form of the statem€nt is +include < file nane> +include " f i1e nane' The less than () and greater thar (>) sign delimiters indicate that the f,le to be included is part ofa standard library or set oflibrary files. The compiler will typically look for the file in the "\inc" directory. VVhen the lile name is delimited within quotation marks, the compiler will frst look in the same d;rectory as the C 61ebeing compiled. Ifthe frle is not found there, then the compiler will look for the 61e ir the default library directory The #include statement can be located aq'where in the code, but it is tt?ically used at the top of a program module to improve the program readability. Sta"dard I/O and Prepnceßor FLnctian! 3.6.2 THE #DEFINE DIRECTIVE A #define directive should be thought ofas a "text substitution" rdered to asa "macro." The standard form ofa #define is +define NÄ!4E Reptacenen! 1'exc Typically, #defne directives are used to declare constants, but the tag tvevr" and the "Repläcemen!_Texts" may also have parameters. The preprocessor will replace the tag "NAME"with the qxpansion"Replacenent rext"whenever it is detected during compilation. Iftvavr" contains parameters,the real ones found in the program will replace the formal paraneten written in the text "Replacement Text". There are a couple ofsimple rules that apply to macro definitions and the #define directive: . Alwaysuseclosedcomments(/ . . . . . /) whencommenting the lineof a ttdefine. . Remember that the endof $e lineis the endof tJ|e#detine andthat the r€xt on the left will be replacedby o/ of the text on the righL For eranple. given the folJowingmacrodefinitions +define +define aLPHA oxff /i SUü (a, b) a+b nask off looer nask off bits */ the following er.?ression intx=ox3def&aLPEA; would be replaced with int x = ox3def & oxff /* lower bits r/ ; änd this c.rpr€ssion inl i=sUM(2,3 ), would be replacedwith int i=2+l; The diversity and capability ofthe #defne directive is somewhat dependent on the sophrs tication of the compiler's preprocessor-Most modem compilers have the ability to redefine functions and operations aswell as the abillity to sort out the panmeteß that go with them (as in the examples above).The CodevisionA\R compiler is very capable in these areas. Lesser compilers may only allow the simplest operations, such as dcfining constants and strings. Using a #def,ne to ,liäs functions (createaltemate calls for functions) can be a powerirl and handy thing! For example,an existing tunction in a library may appear as int t _vrire return SCIl(inl c) // / / this function an a || e, ndtF c; J Giving the function an alias * d e f i n e p u t c h a r 2( c ) write scrl(c) sends a char .om. por to 189 t90 allows the function to be rcfered to in two ways: putchar2 ('b ); write_SCI1{'b ); This is quite uselirl when reutilizing code from another prcgram or combining several li braries in a large development Instead ofthe locating and renaming ofevery call oi refer ence, the fuoction was simply given an alias, allowing it to be r€fer(ed to in more than one This useof#define can also enhancethe readability ofa pmgram by allowing a function to be 'ie-declared." Letl; assumea funcnor. called$t_rolLcolj placesthe cursor at a position on a four-row by twenty-character LCD displny basedon two prrneters, a rro ar\d ^ eolamnl void set row co1(char row, char colunn) t l With the use ofa macro to form a re-dedaration, the positions on the LCD display can be rclened to as an r and y coordimte instead ofa row and column: +define qoEo xy(x.y) set row col(y,x) Another possibility is a re declaration that carr use a charact€r position to set the cursor: {defin6 s6l ^häJ pos{p) {(p,l0l,,pg20', The row is calculated by dividing the character position by the number ofcolumns, and the column position will be what is left, a modulus tunction of the width. This is ,11done as a function of'fancy tcrt substitution."The compiler seesonly what is on the right side ofthe #defne, becausethe preprocessordid all the work aheadoftime- These changesin rcference potentirlly male the program more understandablenot only to the programmer but to oth ers reading the code aswell. The substitution process crn be even more findy controlled. When defning macros, you can use the # operator to convert th€ macro parameter to a character string. For arample, +define PRINT'MEssacElr) printf (+r) will substitute this expression P R I N T _ M E S S A G E( H e 1 1 o ) ; with priD!f ("Hetto ) ; It is also possible to concatenate two prrameters using the ## operator. In the example below, the formal parameters'a" and'1" are to be concatenat€d.In the substitution, the left side, "alpha(a,b)", is effectively replaced with thc right side, "ab". In the program, the real sta"datd l/O and Pr.?ta .',o fn4. tu4 parameters x änd y are used. So the macro delinitior cha! =1; alpha(x.y) wiLIresultin char xY=1; Typically, a replacement text is defned on a single line along with the tag name. It is possible to erlend the defrnition to a new line by using a ba&slash (r) at the eod of the line: +define MESSAGE "This is a wery \ L o n q t s e x t .. - ' The backslashcharacterwill not appearin the expansion,and the new line characterwill be eliminated as well. The result is that "This is a very long tä:1..." wifl be treated as a single, unbroken string. A macro can be undefrned using the #undef directive. This feature is primarily used in conditional compilation where a tag name is used as a flag: The #undef dnective allows a previously defined macro to be rede6ned. For instance, if a maao was defned as *define A CHAR A you could redefine it to a lower case a': +undef +define A CHAR A CHAR 3.6.3 THE #ifd€f, #ifndef, #else, AND #endif DIRECTIVES The #iftld, #ifndef, #else, and #endifdirectives can be used for conditional compilation. The syntat is lse! of statenenhs 1l lset of staLenents 2l If"macro-nane" is a defined macro name tllen the #ifddexpression evaluates to TRUE and 2" 1" willbe compiled. Otherwise, the "set-of-statements the "set-of-statemenls stabemenEs 2" ,re optional. Arother wiJl be compiled. The "+else" ,nd "set-of +ifndef If"macro-nane" nacro nane lset of sEaEenentsl is not defned, the #ifndefexpression ev"rluates to TRUE. The rest ofthe syntaxis the sameasthat for #ifdef. The #i{, *bli{, #else,and#endif dnectiws can be used l9l t92 for conditional compilation. +if expressionl lset of statenents 1l +e1if exp.ession2 lset of statenents 2l lset of statenents 3l ewaluates to TRUE, the "set of statements If'expressionl" 1" will be compiled. will be compiled. e!'aluatesto TRUE, the "sets of,statenents-2" 'sets-of-statements-:" will be compiled. The "+erse" and Otherwise, the "se! of,stsatenents-3" areoptional If"expression2" Conditional compilation is very usefrl in creating one prograJn that runs in severalcon6gurations. This makes maintaining the pmgram (or the product the program runs in) easiea since one sourcecode can apply to severaloperating configurations. Anothe! more common, use of condidonal compilation is for debugging purposes. The combination of condltional compilation and standard VO library functions cao help you get a prog:am up and running faster without equipment such as in-circuit emulators and oscllloscopes. The er<amp1e state machine used to cortrol an "imaginary" trafic light (from Chapter 1) could be modified to add sornedebugging crpability. Using conditional compilation, the debugging featues added could be tumed on and off asneeded,trading between providing information and increasedperformance, as shown in Figure 3-1: +lnc1ude <neera8535.h> +include <de]ay. h> /*ilatafin€ /. DEBncsrNGoN r/ Ronowins the couert sill caq3e tbe DBaueGl$G_oN'f1.9" to b. 6nabloat. Tllia wi].]. cauae tüe c@Di1er to iacludl€ lho tb€ addlltloDaL 1lblaly aDal rises ot coate reqriled allöwing ,/ frd tb€ uaItT. to wetcb tüe atate @cbire 4E I)rogtader *ifale! DEBOeeING-Otr th€ Etandl.ral /* iacluile ittlclual€ <€talio.b> c I/o *def,iae xtal 4000000L *alefiDe baual 9600 Figure 3-f Exponded",maginotyTtofrc Wt" /* /* fulctloD alaflaitioD6 quartz crystal Baud rate */ Softwarc(Co inues) fr€qu€Ecy */ IHzl */ S/ard'd +define Eti_RED LITE +define EIi_GRN_LITE PORTC,2 #define #define NS_YEL_LrTE poRTc.4 Ns GRN_LITE PoRTc.5 +define +define +define PED xING_Eüt PINA.o PED XING NS PINA-1 FOUR-WAY sToP PNA.3 char tine int cutent char flash left; state; toggle; PORTC-o /* /* /* outspurs */ push burLon crossinq push burron crossinq input for 4 itay Srop */ */ */ alefinirions /t /* /* I/o znd Prelro.erlar F"n.tians pedesrrian pedesrrian /* swirch rö acrual tine in secoDds spent in each state */ cuftent stare of Ehe liqhLs */ toggte used for FLASIIER srare enumeration creates /* lhis a sinple way to add srales ro rhe lry nane. generatse EnumeraLions an inteqer vatue for each nane t/ automaticatly, making the code easier to naintain. ENUN { EW MOVING , EIi.WARNING state nachine /; The actual void Do states (void) I svitch ( current_sta!e) { _dse EW MOVIN.: Eä_GRN LITE NS_GRN,LITE NS_RED_LIaE E!'i_RED_LITE EW YEL_LITE IüS YEL LITE if(PED { = = = = = = is 1, 0; 1; 0,. 0; 0; , NS_üOVING he.e.. /. edst /* north , NS !'ARNING , nachine FLÄSHER }; */ wesr häs south thc has a,eel */ the red! I XrNG_EW ll FOUR WAY STOP) /* pedestrian wishes ro */ a 4-way stop is required > 10) if (tine left = 10; tine teft /* shorten the tine ) if(tine,left != 0) /* count dovn the tine */ t , tine_1efr; .eturn; /t return to main */ I / r tine expireal, so.. */ */ = 5; tine_teft /r give 5 seconds ro WARNTNG = EW WARNING; current-stsace /* Eine expired, nove */ break; /* to Ehe nex! state */ Fieure 3-t */ E ponded"lna$noryTtofflc Lidht'softworc (6ntinues) */ 193 t94 CASE EI'I WARNING: EW ORN,ITITE NS GRN-I/ITE Ns RED_LITE EI,I-RED_LITE EIiI_YEL_LITE NS-YEL-IITE lf(tine = = = = = = left 0; 0; 1; O; 1; 0; /* north-south /* anal east-wesr != 0) /* count has lhe has do@ lhe the r/ red,, */ yellow */ tine I tine_left; return; */ to nain /+ ieturn */ so.. / " tine expired, J itiFouR_waY_sToP' /* if 4-say requested Lhe. = FLASHER; /* Ehe flasher current state | J break; case */ /* orhervise-. = tine lefl 30; /* sriwe 30 secönds Lo MovINC = NS-IIOVING; cuüeDt-stsate expired, nove i/ /* tine i/ /* to the next s!a!e NS_MOVTNG: EW_GRN_LITE NS_GRN_LITE \S_RED LITE EL{ RED LITE Et{ YEL LIIE NS-YEL-IJITE if I = 0; = 1,' - 0j = !; = 0; = 0; /r /' lefl != 0) /* count down the the tine */ ' notth souLh h"s the s'eenll easE sest has the redl I */ l PED_XrNG_NS ll FOUR_$IAY STOP) a pedestrian vishes to /* if i/ a 4-way stop is requireal.. if{tine lefL > 10) = 10; tine left /* shorEen t if(time ' srd.*/ tine */ */ { tine-1eft; return; /* return ro main */ so.. */ / * tine expired, \ = g i v e 5; 5 secoDds lo I'ARNING r/ tire_left /* = N s W A R I I I i I G ; current_state /* tine expired, nove */ break; /* to lhe nexl stale */ CASE NS WARNING: EN-GRN-LITE Figure 3-f = 0, ExpondedlmoginoryTafi.U€,lt'Sotutore(6ntinues) Standad I/O and Pr.?rat"t ar run tior\ LITE LITE LITE LITE LITE NS-GRN NS_RED Eit RED Eit YEL NS YEL = = = = = 0; 0; 1; 0; 1; != if(tine,left tine retu.n; /r north-south /' anal east-west 0) /* has has the alown the coun! */ yellöw.. the */ red.. rine */ left; !o nain /* return "/ r/ expired, so.. /* tine I ir {FoUF hAY STOP) /r 'l 4-wäy requested tqc- slar*/ = FLASHER; /* Etle flasher cullents-stsatse I Eiae-left current I break, EW Ns Ehl NS GRN cRN YEt YEt LITE LITE LITE 'ITE = = = = */ /* olhervise.. = 30; /* give l0 seconals ho MOVING +/ = EW üOVING; state exrrired, move */ / * rine t o t h e n e x t s E ate */ /r 0; 0; 0; 0, /a /* ^= 1,' /* flash-tossle if (flash togqle & 1) aDd t/ */ off ye11ow att green lices Eoqqle LsB-. */ { NS RED LITE = 1; E!{ RbD-LTTE - (. /* blink NS-RED-LITE = 0; FII_RED LTTE - 1; /* allernately red J else 1 ) if(lFouR irAY STOP) cülreot break; current,state b!e"ki /' sel statse /* if = NS WARNING; äny unKnown staLe lierhts */ */ no tonser a 4-wav slop '/ = EW-WARNING; /* then reluln ro to ] (Contkues) Expdnded"lmoCinotyTnffß UCht'Softwarc */ nornal d good onell ) Figure 3-f I ' 195 t96 nain (voidl void { D D R C= o x F F ; DDRA= 0x00; /* /* porrc polra att att out */ in */ *1fal6f DEauceING_O!| tbe ueART.6 baral rate /* lnlrializ€ UBRRE=O t nBRRrr=xral/16lbaual-1t /* Initiali.ze ttre USART control Rx & |!x eEabled, ao iateEupts, */ I d.r. bitE UCSRB=0x18; */ lsgister frü6 fo@t, /* hitializ€ a data bits, 1 atoD b1t, aslEcbronöus oDeratioD aual */ ao Dality ItCIRC=Oxa5t DriEtf{ *warlllg cu!!enL ncdpite! "Dobug tdte - ver6ioD t,riEtiDs i6 is %al\!\r", oa.! ; _coDEvIsIONAVR__) Ns WARNlNc;/' initialize Lo o good s-o-rirg ' (as sdle qs Po-siblal s(d.e { deray_ns(1000); Do staLes{), this /* l second delay-line be used fo! other oeadeo p o.csses couLil /t call the slate nachine, it knows where it is and whar ro do nexr */ llitde! DEBvccIl|c oN seaal atate alal tln6 ilata /. to seriat DolE */ g a l = state :i, cu*eEt_erete); Dliütf(rculleat = %at \rf, (iarlride_left) l.efr trinrf(i9ire t ) Fieurc t-t E ponded"lnsgnoryTrofr.ECht'Soflworc(anühued) 3.6.4 THE #pragma DIRECTIVE The #pragma directive allows for compiler-specific dir€ctives or switches. #pragma statements are very compiler dependent, so ylou should always refer to the compiler user'sguide when using these controls. The controls described below pertain to the CodeVisionÄVR compiler but will be characteristic ofwhat can be found in other compilers. Stoadzrd I/O and Pte?ro.essar Fxntt;ont ':pragma warn The #pragma wam directile enables or dsables compiler wamings. This would be used to disable warnings that may be viewrd as a nuisanceby the programmer. These can include 'variable warnings such as declaredbut never referenced or'possible loss ofprecision." Dis abling the warnings should not be done on a permanent basis;it could causea useiirl warn ing to be missed, leaving you wondering why your program is lelding bad results.The best courseof action is to dedare, code, and cast until the warnings are all gone. #prasna warniiiite /i sone here */ enabled t/ code are /* Irarninss +p!agna tarn+ #pragma opt The compilert code optimizer can be turned on or of using the #pragma opt directive. The optimizer is responsiblefor improving the compiler's generatedassemblylanguageoutput. This is accomplished by reducing the assemblyoutput size, ananging it to run faster, or both. The #pragma opt directive must be placed at the stärt of the source6le, and the default is optimization tumed on: ' -. +pragna opr : opt- zd iön o'f, for fe-rinS purposes ' +pragna opt+ #pragma optsize A program that is optimized for size may actually run a litde slower becausecommon code is converted to subroutines, and subroutine calls replace the common code. A program that is more "in-line" (not optirnized for size) runs faster becausethere is no additional overhead from the calls to and returns &om subroutirrs. Ifthe code optimization is enabled, you can optimize some ofthe program, or all, for sze or speedusing the #pragma optsize dir€ctive: /* The ploglam will 'praqma oprsrze+ /* Place your progran /* Now the prosran be optinized vilf funcrions for nininu( size */ here '/ be optlnizeal for naxinum execulion speed */ 197 t98 +pragna /r optsize your Ptace p.ogran funcEions */ here The defaultstateis determinedby the ProjectlConfgurelC CompilerlCompilation IOptrmization menusettingin the CodeVisionAVREnvironment. trpmgmasavereg The automaticsavingand restoringof registersR0, R1, R22, R23, R24, R25,Pi26,R27, R30,R31, and SREG during intemrpts canbe tumed on or offusing the #prägmasavereg directive.This control is usedto manuallyrcduceany potential excessoverheadassociat€d with savingandrestoringthe machinestatein an intemrpt sewiceroutine.This car bedangerousto the novice,so somecarefirlstudyofhow the compilergeneratescod€shouldbe donebeforeyouusethis"guruJeveJ'controL ' .t.rn +pragna ince!!upc lines in J-qisters saweres savinq ott ,/ void ny_irq{voidl I only lhe teqisters thdf äre ä, ...ed by .1e che handler, for exanple R30, R31 and SREG r/ Ill Lou push 130 push 131 in !30, SREG push !30 /+ place /* now lesEore Ehe C code here */ SREG, R31 änd R30 */ pop r30 o u t S R E G ,1 3 0 pop r31 pop.l0 J ' 'e-e1-ble +prasna !eqistFr saving lor Lhe orhe! inr-rr.p s ' save.eg+ The default state is automatic saving ofrcgisteß during intemrpts. The default state ofthis compiler setting is "savereg+",and there is no menu option for this seaing. Care must be used to make sue that this setting is "savereg+"when its function is no longer needed, to prevent effatic operation ofyou proglam from registers not being saved. St'ndald FLf,rtiant I/O and Pftlr.cesar #pragma regalloc The CodeVisionÄVR compiler will try to use register variables to increasepeformance as often as possible. There may be instances, like debugging with an In-Circuit-Emulator (ICE), where register variables may become difficult to Eack, so you might wish to di'ect the compil€r to not perform this automatic register allocation. The automatic allocation of global variables to rcgisteß can be türed on or off using the furagna rega oc directive: ' rLe oiiow'a9 to atlocated +prasna slooäl a .egister vä':ablF */ wil. ba autordl:c"1 v variable 6nd will will nor be autonalical1y j. ao d oa ple\ed SPEV resaltöc+ /* the following d"a.atpd a a g1oba1 'pgislFr reqalloc *pragna unsiqned cha! t'eca; The default state is determined by the PmjectlConfuurelC Compilerl Compilation lAutomatic Register Allocation check box setting in the CodeVisionAVR Environment. #pragma promotechax The ANSI standard for the C language treats characten as 16-bit values.This is not necessary (or even desned) in a small, embedded system.The default settings for the CodeVi sionÄ\rR compiler are to leave a character a character,but ifan application requires characters to be treated as integers, there is a method ofenforcing the ANSI standard. The ANSI character to integer operandspromotion (or convenion) can be tuned on or off using the #pragma promotechar directive: /* turn +p!aema oo the aNSI p!onotechar+ turn /i *pfagma off the ANSI plonotsecha. char char pronotion int to to int pronotion This option can also be specilied in the ProjectlConfigurelC int menu setting in the Code\GionAVR Environment. */ */ CompilerLPromote char to #pragma uchar When character variables are declared,the default format is as follows: // unsigned char var2; de.ldLes // o siqned declares an cha dctet u.siqned J- idb character a variabLe 199 200 The #pragma uchar directive allo*s the default format to be changcd as it pertdns to charactcrs. If the uchar directive is enabled, the following format is now in eflect: sisned char c|'ar nar2, var; // and // Lhis is now a signed characrer variabte this is an UNSTCNEDcharacrer variable uchar can bc turned on or offusing the #pragma uchar directive: /* char +pragna uiLL be unsiqned uchar+ /* char #piaqma \di1L be sisned uchai- by */ default by defaulL */ This option can also be speciied in thc ProjectlConfgurelC Compiler char is unsigned mcnuin the CodeV:"ionAVREnrironmen.. #pragma Jibrary You may wish to create1'our o*'n function library to be used as commonly as the standard I/O library Once 1'our library has been created, it can be included in thc progrnm at com pile timc using the #pragrna library directive: The creationoflibraries is compiler speci6c;you shouldrefer to the compiler usert gurde for instruction on the required methods3.6.5 OTHER MACROSAND DIRECTIVES Table 3-3 lists somepredeined macros.These tag namesare specifrcto CodeVisionAVR but couid be lound in other conpilers. These can be used to get information, such as the compile date and time, into the compiled program. They can also be Lrsedto conditionally rompi'eba.eJon memon modelor oprimizarion .enings. CodeVisioru{VR also supports the directi'es #enor, #waming, and #line. The #erfor dircctivecan be usedto stop compilationand displayan error rnessage. The slntar is +error elror messase For example, +error This is an erfor Similarly, the *$aming directive causesa warning messageto be displayed, but does not causecompilation to stop. Thc sptax for the #warning dircctive is +warninq warainq nessase For example, the compiLation. Standard I/O and Pt.Ptates'or FLn.tian! the Eßion md Bision ofthe empiler repftsentcd as an integer, for mple V1.24.0 is rpßented as 12.10 CODEVISIONA\'R_ LINE FILE TIME DATE the l:llmt ßUILD the build nuoberofthc compild line nrnbd of tle conpiled file thc (1rent compited 6le dmc in ,r.''.$ thc üot fomat the cuftent date,n zz 1//))j/ format the clock ftquenc,v speificd io integ€rin Hz assetin rhe MCU CLOCK FREqUENCY MODEL TINY _MODEL_SI'IAI-L OPTIM]ZE_SIZEOPTIN,IIZESPEED. HEAP START HEAP S1ZE U}TSIGNEDCHAR ser'fcompnedc'ng thcTrllv mmory modd st ifconpiled ßing the SMALL mcüory modd setifconpil€d with optiniation for size set ifcompiled wiih optimiatior for steed the hap staning addres the hap sia s set in the compiler options sct if@mpiler option is enabled or #pntna set it thc I bit mms uchd+ is uscd compiler option is enabled or #p.rgna 8BIT ENUIIS Table 3-3 CodevisionAvR Pre,lefined Moctos Finally, the #!ine directive modifies the prcdcfined " displayed in Table 3 3.The qntax is 4l - -9-r r .onsldnr l"fil- LINE " and "-FILE-" macros as ndna l For example, set /: rhis nilt +1ine 50 fi te2. c /* '.7 this vrlr CHAPTER set LrNE- tso s0 and -FrLE __LrNE__ to Lo "fi1e2.c i/ 100 SUMMARY This chapter has provided the knowlcdge necessal for ],ou to use standard 1ibraryfunctions for printing information, gnthering user input, and debugging your programs. You have aiso learned how to modi$, the rcot tuncircr's of getctar) and puxbar) such.that the standard library can be used on a variety ofhardwarc configurations. You have learned about the use of the complier directives #inctude and #define and how they are used to add reusabiliqv alrd readability to your programs. You have also learned ebout conahtional compilation using #fdef #ifirdef, #dse, and #endif, providing a method for having a single source code be used for a vaiety of system conligurations or for adding temporary code for debugging purposes. 2l 202 #pragma statements were also described so that your code could be generalized or oprr mizrd during compilation, yielding the best reusability and performance from your 3.4 EXERCTSES * | . Wrire a macro usingthe #define directiveto aliasthe function putchdr0with a function namedsend_the_chdr(l(Seaion 3.5). 2. Write a functionthat promptsthe userfor two inregervalues, addsthemtogerher, andprintsthe r?lu€sandtheir sumin the format"ThevaluesA + B = C",wh€reA,B, andC aredecimalintesers(Secrion 3.4). 3. Write a funcrionrhat usessconf0to receivea date in the format"MM/DDmffY" and thenus€sprintf(lto display th€ date"DD-MM-YY"(Section3.5). *4- Writ€ a functionthat prinB irr compiledat€andtime.L.Jse the compiler's internattag namesto get the dateandtime values(S€ction3.6). 5. Write a functionthat prin$ its compiledmemorymodelandoptimizersettings. +6. Write a functionrhat'nputsa l6-bit hexadecimal mlueandth€nprintsthe binary equival€nt. Note:Thereis no standard oueurfunctionto print binary----6o it is all up 7. Usea #define to declarea paiällel, &bit l/O port,PORTX,at location0x l200.The d€clarätion shouldb€ madesuchthatthe port canb€ accessed by"pORTx = 34",or "i = poRTx" (Section 3.6). 8. Write a funcrionto initialize the USARTon theATmega8s | 5 for I databits,I stopbit, no parity,andasynchronous opemtion.Th€ baudrateshouldbe setfor 9600baud with a systemclockof 4MHz.Transmir andreceiveshouldalsobe enabled.Utilize the macroto ?utomaticälly get the !"lue for UBRRL _l'4CUCLOCK FREQUENCY lsection3.6). 3.9 LABORATORY ACTI\'ITIES l. Createa progrämto ourputtheASCIIchaEcter"c" every50 milliseconds thrcugh the USARTObsedeboththeTTLl€v€lsignalon the microcontroll€rbTXD lineand the RS-232 sitnalat the outputof $€ mediadriverusingan oscilloscope. On eäch waveform,id€ntifytie stan bit, th€ stop bit, andthe dat bits of th€ transmitredsignal. 2. Modirythe pro8rJmin Activity I so that the "c" is alsotransminedfrom the SPIbus. Usethe oscilloscope to displayboththe tränsmittedsignalandthe €lockandidentify 3- Createa proSrämto usegetcho4)to get a serialchamcter(from the PC) andput(hor0 to return a €haracterthat is two letrersfunher atongin the alphaber 4- l'4odifythe programfrom AcrMg I by changingpu.cfisr(lso that the code for the ASCIIcharacterb€in8returnedappears on port C,whereit couldb€ conveniently readby attachingLEDS. Strada l I/O and Pre?rccesar Fan.tiahr 5. Createa programthat usesa parallelge&rro.oto get a byte of datain on PORTAand usesthe "stock' purchdr0to echo what it receivesto the USARTat 9500 baud.Use is externalinterrupt0,setto triggereitheron a risingora hlling€d8e(whichever convenientto your hardwäre),ästhe st.obe thät causesPORTBto be readandthe datatränsmitl€d through the USART Createa parallelport versionof pukno4?alongwith the ge.cho.0(fromActivity 3) to output the data readfrom portA on port C. 7. Teamup with a pannenOne of you shouldcreatea SPIbustmnsmitter program,a modifi€ationof the programfrom ActMty 5,that usesthe SPIbusto transmit the datafrom ponA when the appropriatesignalis receivedon the ext€rnal interrupt. The other partner should cr€atea SPIbusreceiveca modificationof the program from Activity 4, that displaysthe data receivedover the SPIbus. 8. For a real chall€nge,us€th€ programsfrom Activiq/ 7 and cr€atetwo-way communicätionwhereboth microcontrollers reädthe dataon ponAwhen trigSeredbytheir own ext€rnal interrupt and sendit through the SPIbus.Both microcontrollersalso displaydatärec€ivedby me-ans of the SPIbus. ändpuEhar0usingthe SPIpon ofan ATme8a85l5 or 9. C.eateä versionofgetchorO your Pärticulär Processor t 0 .Createa programusingActivityI that sends"CRules!!"out ofthe SPIpon usingthe Duts0function. Createa programusingActivityI that s€nds"CRul€sthistime ddd!!"out ofthe SPI poft | 00 times,wh€redddindicates whichtime,from lto 100. 203 The CodeVisionAVR C Compiler and IDE 4.1 oBJECTIVES At the conclusion ofthis chapter, you should be able to . Operatethe CodevisionAvRc compiler and int€grateddevelopment environment . Correctlyutilizeth€ compileroptions . Apply the CodevisionAvR€nvironmentto progr:m a target device . Apply the CodevisionAvRcodewizard to automaticallygenerateshellsof code . Applythe CodevisionAvR terminaltool to sendandr€c€iveRS-232 communrcaüons . Performbasicdebugsin8operationsusingAtmelt AVR Studioas a software simulator 4.2 INTRODUCTION The purposeof this chapter is to fämilirrize you with the CodeVisionAVR C Compiler The CodeVisionAVRC Compiler is just one ofmany C compilersarailablefor the Atmel A\lR microcontrollers-lts outsunding developmentenvironmentand superb compilerdeterminedits usein this text. Ur ike a genericcompilermodifed for the AVR instruction set, CodeVisionAVRwaswritten specificallyfor the A\rR microcontrollers.As a resrilt,it producesvery precisecode,usingthe manyfeaturesofthose microcontrollerswithout waste.In comparisonwith other compilers,it produces smaller,more efEcientcode for the Atmel AVR microcontrollers.Finally, CodeVisionAVR hasthe Code\MzardAVRcodegenerator,an inaluable tool for jumpstartingmostprojects. 20s 206 This chapter provides a look at the CodeVisionAVR developmentenvironment and its many features.You wi1l learn how to createa project,to set specificcompiler options for the project, to make^ project into an output file, and to load that output fi1einto the target device.The CodeWizardAVR code generatorwill be discussed,along with the terminal tool. Finally, you will be shown somebasicfeaturesofAVR Studio as a softwaresimulator. Currently, CodeVisionAVR is designedto run in Windows 95, 98, Me, NT 2000, and XP environments.The version on the enclosedCD-ROM is the evaluationversion.It is limited in the size of the sourcefi1ethat can be compiled and in the number of featuressupported by the CodeWizardAVR codegenerator. 4.3 IDE OPERATION The CodeVisionAVR C Compiler is accessedthrough its integrateddelelopnrentenztironnent (IDE).ThelDE allowsthe userto build projects,add sourcecodefi1esto the projects, set compiler options for the projects,compile, and makeprcjectsinto executableprogram files.These executablefiles are then loadedinto the target microprocessor. The goal ofthis sectionis to familiarizeyou with the usualuseof the CodeVisionAVR IDE. There aremany advancedfeaturesin the IDE that are beyond the scopeof this text. As CodeVisionAVR'sIDE is discussed,the menu items are referencedby the main menu name followed by "l" and the submenuitem name. For example,a referenceto the Save As menu item within the File menu appearsas FiIe lSaveAs. The main menu bar for CodeVisionAVR's IDE appearsbelowrÄi applicationtitle bar. 4.3.1 PROJECTS A project is a collectionoffiles and compiler settingsthat you useto build a particularprogram. A few projectsareprovided for you on the CD-ROM includedwith this boolq but it is alsoimportant to know how to createand configurea new project.All project 6les havea .prj extension. An open project appearsasin Figure 4-1. Notice the file navigatordown the left side ofthe screen.This lists the fi1esthat arepart ofthe project aswell asother files that arebeing used with the project. Only the files listed under the project name are to be compiled as part of the project.In Figure 4-1, the project name is IOM and the sourcefiles for the project are IOM.; cp.c,LCD.c, and,heypad.c. The files listed under Other Files are not compiled as sourcefiles for the prQect(ihd.h andcp.Z).The sourcecodeeditor occupiesthe right side of the screen.Many sourcecode files can be openedat once and tiled, stacked,or maximized dependingupon the user'sneeds.Acröss the top ofthe screenare the menus and the toolbars,which are referencedthroughout this chapter Finally, acrossthe bottom appearsthe Messagestab.This is where the compiler errorsand warnings are listed upon compilation. Open Existing Projects Selectthe FilelOpen menu command or click the Open File button on the toolbar to open an existing project file. When either of these is performed, an Open File dialog box Tbe CodeI/isionAvR C Compiler and IDE EEoJ.cr 3.s.ic : :ö-nq.-sE lr.jet . ü !r .oorEtr c&E h 3 lir äddrioa cdiE Figure 4-f mäyE ßqrE mayb. raqri.d An OpenProjeain CodeVisionAVR appears.Browseto the appropriatedirectory and selectthe project file to open.\Mhen you open the project file, the project appearsasitwas last used.Figure 4-1 showsa g?ical open project. Notice the file navigatordown the left side listing the project name and the available files. Create New Projects New projects are createdwith the File lNew menu command or by clicking the Create New File button on the toolbar. These actions open the Create New File dialog box as in Figure 4-2, r€questingthat you specifr the tJpe of file to open. Selectthe Project option and click OK A seconddialog box asksyou to confirm use of the CodeWizardAVR to createthe new project. This dialog box is depicted in Figure 4-3. The code wizard is a tool used to automatically generate part ofthe sourcecode for your project; it is coveredin more depth later in this chapter. To create a project rüithout using the code wizard, select No when prompted to use it. A final dialog box prompts you to speci$'a project file name and location. 207 208 Figure ,f-3 Figure 4-2 CreateNewFileDiologBox Figure 4-4 CodeVisionAVR ofter Creotingo NewProject CodeWizardAVR ConfirmDialogBox When these steps are completed, CodeVisionAVR creates a new project and opens the Configure Project dialog box for the new project. This dialog box has severa.ltabbed frames of options that allow you to customize the project for your specific application, as shown in Figure 4-4. Configure Projects The project is configured with the ProjectlConfigure menu command or the Project Configure toolbar button. Selecting either of these opens the Configure Project dialog box. The CodeltlionAI,R C Can?ikr and IDE There are three tabbed fiames in this dialog bo* Files, C Compiler, arrd After Make. Ifyou select the Files tab, you are able to add source frles to and remove source 61esfrom the project. The C Cornpiler tab ,llows you to set properties for the project pertaining to the target device and the executable program file. Finally, the After Mxke tab allows you to selectparticular programs to run (such as a chip programm€r) when the makc is complete. The Files and the C Compiler tabs are covercd in mor€ detail later in this chapter Close Project To quit working with the currcnt project, use the FilelClose Pmject menu command. Ifthe project liles were modificd and were not yet saved,you are pronpted to savethe modified files. When you save,the IDE createsa backrp fle with a /r- extension. 4.3.2 SOURCE FTLES Source 6les are the 6les that contain your program sourcecode-They are the {il€s that you painstakingly labor over to make the microprocessordo the right thing. The IDE allows you to add sourcef,les to the project and remove them from it. The IDE also has a fairly powertu1editor built into it for editing code-There are features ofthe IDE editor that are very specific to a code editor and are useful in developing and debugging code. Open an Existing Source File To opeo an existing 1ile, use the Filelopen menu command or dicl< the Open File button on the toolbar. An Open File dialog box alorls you to browse to the directory to locate the file to open. Selectthe 61eand click OK to open the fla Altematively, single clicking the frle name in the navigator also opensth€ fle. The file opensin an editor window within the IDE. Although many 6les are open in the IDE in Figrue +5, 4,r is the cunendy selectedfile. The selected6le path and name are listed in the tide bar at the top ofthe editor window. Create a New Source File The File New menu command and the Create Neu/ File button on the toolbrr are available to create a new sourcefile. When either is selected,a dialog box appeärsprompting you to selecta 6le gpe. Select Source and click OIC A new editor window opens for the newly created 6le, as shown in Figure 4-6. The tide bar sho\rs the 61e name as rntitled.e, and t \s li.tedin the fiLeravigatorunderOther Fiics. To savethis file under a new name, usethe File lSaveAs menu command. The new fi1efrom Figure 4-6 is shown in Figure 4-7 savedunder the nane nlnezfle.c.Thls changeshows in the tide bar and in the fiIe navigtor Add an Existing File to the Project Simply opening a 61eor creating a file does not automaticrly add ;t to the current project. You must open the project and select the ProjectlConfigüre menu command or click the Roject Configure toolbar button- This opens the Confgure Project dialog box. Select the 209 2t0 Figure 4-5 lhe Source Fih cp.cls Seleaed Figure 4-6 New SourceFileuntitled.c Creoted The CodeVisian'4I/RC Compilerand IDE ,d.r!n ro-t // !!r!._scrr_Äscrrlb.0, Figure 4-7 prrpt tt* F.aa ?.1r. ; NewSource FileRenomed osmynewfile.c Files tab, which lists the project name and the source file names for the project. Files are added to and removed from the project by clicking the Add and Remove buttons on the right side ofthe window. The Project Configure dialog box is displayed in Figure 4-8, with iom.c,LCD.c, ke1pad.c, and p.c listed as sourcefiles for the project. Clicking the Add button and selecting the newly created file myneufle.c adds it to the project as a sourcefile. The new sourcefile list appearsin Figure 4-9. When the Configure Project dialog box is closed, the file navigator shows that the file myneufle.c is now considered part of the sourcefi1esfor the project. In Figure 4-10, the file is no longer listed under Other Files. 4.3.3 EDIT FILES The editor built into the CodeVisionAVR IDE supports the standard editor functions. The cursor is moved around with the Home, End, and arrow keys, as well as the mouse. 2ll 2t2 Figure 4-8 ConfigutePrcjectDiologBox,Add BunonAicked Figure 4-9 mynewfile.cAddedto Projeaos o SourceFile T h e C o d e V i s i o n A VC R C a n p i l e ra n d I D E .oEt ob ddn !ry_rdLtr?l - tordd, Äcsrr rEtrTl Nilod 'DdtU.h0bit*Cn , (.!line iEy bo rcqild Figure rL I 0 lhe FileNovigotorListsmynewfile.caso SourceFile Clicking and dragging the mouse selectsportions of text to be manipulated together. Cut, copy,and paste the selectedtext with the standard shortcut keys, the Edit menu options, or by clicking the right mouse button. Find and replace functions are supported, along with undo and redo editing functions. The editor has excellent featuresespeciallydesignedto facilitate editing code. Some ofthese features make it easier to move around in the file. The Alt+G key combination or the EditlGoto Line menu command moves the cursor to a snecified line number. Bookmarls are toggled on and offat the current cursor position by tLe EditlToggle Bookmark menu command or by the Shift+Ctrl+0 through 9 key combinations. The EditlJump to Bookmark menu command or the Ctd+0 through 9 keys jump the cursor to a previously set bookmark. Bookmarls are usefirl for moving around within the program without paging tfuough the code or memorizing line numbers. The editor has two features to simpliS formatting code for readability. First, the editor allows you to indent and de-indent blocks of text. Highlight the text by clicking and 213 2t4 dragging your mouse, then press the Ctrl+I or Ctrl+U kevs to indent or undo the indent 'l'his on thc block of text bl, one tab spacing. is usef t for indenting the code in rn if starement or whjle statement.Second,the editor supportsan auto-indenting feature,which moves the cursor dnecdy below the start of the previousline when Enter is pressed, insteadof moving the cursorto the very beginning ofthe line. This fexture is controlLecl through the SettingsIEditor menu command. Thc cditor also hasa brace matching feature.Ifthe cursoris positionedon an openingor the closing bracc, thc EditlMatch Braces menu command or Ctrl+M highlights the portion of the text until thc coresponding matching dosing or opening brace.This allows the programmer to check lor balancedbracesaround tunctions, ifstatements, while statements, and so on. Pressing any key or dicking the mouse hides the higNighting. Finalll', the editor has a syntax highlighting fcaturc that makes the code easier to read and write. The syntar highJighting uscs special colors to displa,r.keywords, süings, constanrs, and comments so that thev stand out asyou write and review your code.The colors used for highlighting can be modified through thc Settings lEditor menu command. 4 . 3 . 4 P R I N TF I L E S The File Print mcnu command and the Print button on the toolbar Drint the currentlv ac tive 61eon the delault Windows printer. To print only a section of rhe active fiIe. higl ight thc portion to be printed and select the EditlPrint Sdection nenu command. The current print settings arc modified bv selecting FilelPage Setup. This opens the Page Setup dialog box, which allows you to sclcct whcther or not to print page numbers, pagc headers,and syntaxhighlighting.The PagcSetupdialogbox alsoestablishes the marginsfor printing and the units the1. are measurcd in. Finally, the Printer button in the Page Setup dialog box opens a second dialog box for modifying the printer settings or selecting a dif ferent printer altogcthcr. 4.3.5 THE FILE NAVIGATOR The 61enavigator facilitates displaying ^nd opening soLrce6les. Clicking on the 6le name in the navigtor windor. ma-rimizesor opens the 6le in an editor window. A typical navigator window appearsin Figure 4-11- The project name is listed at the top of the window, with all of the source 61esfor the project listed directly below thc projcct's name. Files that are open but not consideredto be part ofthe project sourcc filcs arc listcd undcr Other Filcs toward the bottom ofthe windorv. If there is a + or - bunon next to the fle mrne, more information exists on the file. This nformation is cither erpanded or collapsed by clicking on the + or -. The information nay includc a list of global variables and tunctions dedared in each compiled C source 6le. (These listings are ar'zilable only after a compilation has taken place.) Clicking on the vari ablc or tunction name higl ights th€ variable or function declaration in the appropriate Tbe CadeVisianAVRC Compilerand IDE Froieclrl0M Notes l0M.c GlobalVarobles Funclions Wämings 6lobalVarlables Jf srEm_address x LCD_FoW x tcD_coL ,f BAUD-HATEZ X DATA_LENGTH2 ,f PAF]TY2 .r 5T0P_EtT52 X BAUD_FATEO Functions \ddrnings fl rco." ables fr.Xy GbbalVar E-f0 Funclions -f{} wr_half -f() wr-disp f0 ihit-display -J{} clear-dsplay - f{} disp-chor - J0 disp-slr -f(l di*p-cstr -.f{} disp-command -.t() set_disp-posilion l-l keypad.c Figure,l-f I FileNovigotorWindow C sourcefile. Errors and warnings generatedduring compilation are also displayedin the navigator window. Clicking on the error or warning highlights the related line in the source file. Figure 4-11 shows an example with some ofthe file branches expanded. The file navigator displays the results of the Find in Files command, available under the Edit menu. When performed, it searchesa1l of the files listed in the fiIe navigator for the specifiedsearchterm. The resultsof the find are listed in the file navigatorwinäow for each file in which the term v/as found. To view the results, click the + button next to the Found line. Figure 4-12 shows the resultsof an EditlFind in Files command performed on the term "sprintf" At the bottom of the CodeVisionAVR window, a Find in Files tabbedwindow appearsnext to the Messageswindow, providing a second listing of placeswhere the searchterm was found. 215 2t6 - /{) fi) ' f0 ''/{) -'-f{) -'-f{} '-.f{) --f{} wr-hdl wr-dbp init-dsplay cleor_display disp-char disp-slr disp-csh disp-command f0 set_disp_position Figure 4-f 2 FileNavigotorWindow ofrerFindin Files 4.4 C COMPILER OPTIONS The compiler must know some key information about the target device in order to generate the appropriateexecutableprogram file. This information includesthe chip qpe, the data stack size of the device, and the size ofthe internal and external SRAM used in the application.The compiler must alsoknow a few things about how to interpret and optimizeihe C code in the sourcefiles for your application. To set the C compiler options for the currendy openedproject, selectthe ProjectlConfigure menu command.The Confgure Project dialog box opens,with tabbedframes for different groupsofsettings. Selectthe C Compiler tab, asshown in Figure 4-13. The two most general settings are the chip and c1ock.The Chip list box selectsthe target AVR microcontroller chip. (Note that the evaluation and lite versions of CodeVisionAVR The CodeVisianAVR C Canpiler and IDE Fites rtcompjter lmer m"rc| codeGeneration rderine I pathsI laa**"a I u**0"" I Gbba{y Fn"q"r6 jI glu f,lock l+ooooar chb: mn------l F th"#----.1 ls]prinlfFeat!res: lint uytu* F- Oyt** Int?rnNlsnAl'i szs llfü- tyt". Ur" -l 0plimizatirn Level: It'tarimet DalöStachsizs Exre'nalsFAhl size li\;/ättiäls T flrF:fäl5RÄ1,1 0plhsizelorl lq; lEd- He€pSize: :l SitVariables size:116 :l chgltoini f- chiri$uf T Fromote coreInstr l_ BbkelumsF gnhanced ,qlocailon 17 ,A{tDmnuc Seqister Suu.tMeftbers l7 !{ofdAliqnFLASH Inrüalizdlic.l T LlseanErlernil9tartup T stdckEndlLd'kers ro,..'urt"l fi ourp,t läilEäääEFll " lint.wdth ffi-E-l xe""*l ?E.pl Figure 4-f 3 Configure ProjeaDiologBox,CCompiler Tob do not support all of the Atmel AVR processors.Refer to httP://,.o,ual.bpinfatecb.ro for information on the processorssupportedby eachversion.)The Clock field refersto the system clock and must also be populated.This is done by either typing in the frequencyor using the up and down arrowsto scroll to the appropriatevalue. 4 . 4 . I M E M O R YM O D E L The required memory model is selectedunder Memory Model. Four rnemory models are implemented:Tiny, Sma1l,Medium, and Large. The Tiny option uses8 bits for storing pointers to the variablesplaced in SRAM. In this memory model,you haveaccessto only the first 256 bytesof SRAM. The Small option uses 16 bits for storing pointers to the variablesplaced in SRAM. In this memory mode1,you haveaccessto 65,536 bytesof SRAM. For both the Tiny and Small options,the pointers to the FLASH and EEPROM memory areasalwaysuse 16 bits, so the memory model selection limits the total sizeofthe constantarraysand literal characterstringsto 64K. However, the total sizeofthe proeram can be the fu11amount of FLASH. 217 2t8 The Medium memory model is similar to the Small memory model except that the Medium memory nodel usespointers to constants in FLASH that are 32 bits wide. The pointers to functions are 16 bits widc under the Mediun memory model since they hold the word addressof the tunction. Undcr word addressing,16 bits are enough to addressa flrnction locatedin all 128K ofFLASH. The Large memory model is similar to the Medium memory model except that it uses 32 bits for pointers to the constants in FLASH and for pointcrs to tunctions. The Large mem ory model can be usedfor chipsrvith 256K or morc ofFLASFI. 4.4.? OPTIMIZE FOR The compiled program is optinized for minirmrm size or ma-rimumexecutionspeedby the Size or Speed option under Optirnize for. It is usually dcsirable to optimizc thc soft ware lor size,becausethe memory on the microcontrollcris limited. \\lhcn optimizing för size, the conpiler meticulously pulls out code that rcpcats in scvcral placcs and creatcs a subroutine for it. Each time the code is needed, a call to the subroutinc is uscd instcad. If you look at the ./sr fiIe after compiling, you will notice many subroutincs that the com piler created for you to savespace.However, each call to a subroutinc costs you cxccution time. So, in some applications,strict timing requiremcntsmakc it nccexary to leavethc codein line although it repeatsitselflater. In thesecases,selectto optimize lor speed,not 4.4.3 OPTIMIZATION LEVEL The compiled progran is optirnized according to the Optimize for sctting ff wcll as thc Optimization Level setting. In general, you want the smallest, fastcst code that thc com piler can generate. Horvever, when debugging in an environment such as AVR Studio, you may want to decreasethe Optimization Lewel since the maximal optimization can make stepping through the application and debugging more dillicult. 4.4,4 PROGRAI4TYPE For devicesthat allow self-programming, the Program T)"e is sclcctcd as either Application or Boot Loader A boot loader application is one that can rcprogram thc main program memory while running fton a higher memory location. This allows the software in a microcontrollo to be updatcd using serial communication to the processor dnectly. Once programmed with the boot loader, the microcontroller can be reprogrammed repeatedly without requiring a special programming cable or even resetting the microcontroller. 4.4.5 (s)printf FEATURESAND (s)scanfFEATURES When Prin6 sPrin$ scanJor srafare required by an application, the full implementation of these functions can be consuming ofthe resources.To minimize this consumptrve effect, the compiler options (s)prindFeatures and (s)scanfFeatures alloll,s you to selcct to \{hat level you need the tunctions implemented. Scc thc compiler documentation lor the exact features supported for each function under €ach option. 7'1" Cod"Yi'io",4IlRC Ca,,?i1,,o"d 4.4.6 SRAl'l Default values for the data stack size, hcap size, and internal SRAM size are chosen by CodeVisionAVR basedon the particular microcontroller sdected.The data stack size is the amount of memoD' to be set aside for rariablcs. For a data-rich appJication that requires a larger than normal amount ofvariable space,increasetie data sta& size.This impacts the anount of memory availablefor the program stack,so increasethe data stack size only by the required amount. Ifyou are using memory allocation functions such as z alaq caloe,or rcal /r., then you will need to reservesome heap spaceasrvell. The :nount of heaPspacerequired is the summation ofall allocatedspaceplus 4 bltes for eachblock ofmemory that is allocated. If erternal SRAM memory is connectcd, speci! the size of that memory If the extenal memory dcvice is slow, select to use thc wait statesby selecting the Erternal SRAM Wait Statecheckbox. 4.4.7 COt'IPtLATtON The Compilation ftame contains mosdy check boxes that enablc or disable particular options. It also contains a Jist box for dctermining the gpe of output file format to be used The Promote char to int check bo,xenables the ANSI promotion of char opcrands to int. Promoting char to int leads to larger code size and slower speed for an 8 bit chip microcontroller like the A\rR. The char is unsigned check box selection causesthe compiler to treat, by default, the char data gpe as an unsigned 8-bit variable in the rangc 0 to 255- lfthe check box is not selected, the char data qpe defaults to a signed 8 bit variablc in the range -128 to 127. Tieating char data rypesas unsignedleadsto better codesizc and speedCAUTION: There are some conditional statements that do not oPeratepredictably on unsigned char data t-r,pes.The'geatcr than" and "less than" conditional statements arc two such statements.If a variable is to bc used in this type of statemcnt, it is preferable to use a signed char data qpe. If the value rvill cxceeda signed char data type, promote the variable to a signed integer This seemstuivial, but it could saveyou hours ofdebugging time. To reducecodespace,enumcrationscan be setup to bc 1 byte insteadof2 by selectingthe 8 bit enums option. This should be done witl the understanding that any cnumerated values under this scheme shouid be treated in nath and all other operations as characters and not integers. Some of the AVR microcontrollers support an enhancedinstruction set.To take advantqe of this, you need to select the Enhanced Core Instrtructions check box. It allows enabling or disabting the generation ofEnhanced Core instuctions for microconüollers such as rhe Atrnega128, Atmega32, or AtmegaS. This check box is available ody when a microcon troller that supports the enhancedinstruction set has been selected. Word Align FLASH Stuct Members is an option that makes compilation baclomrd compatible to previor.rsvenions of the compiler where FI-ASH smtctures had to be wotd aligned. This option should not be selectedfor new projects. 120 For debugging purposes,the Stack End Markers check box causesthe compiler to place the strings "DSTACKEND" and "HSTACKEND" at the end ofthe data stack and the hardware stack areas.\Arhen you debug the program with an emulator or simulator like Atmelt AVR Studio, you can seeifthese strings are or.erwritten and modi$' the data stack size accordingly. When your program runs conecdy, you can disable the placement of the strings in order to reduce the code size. The File Output Format(s) list box selectsthe formats for the files generated by the compiler. Most in-system programmers use Intel HEX formaaed frles. COFF is required by the Atmel AVR Studio debugger;ROM and EEP are required by some in s)ßtemprcgrammers. 4.4.8 MESSAGES TAB The generation of warning messagesduring compitation is enabled or disabled by the Enable Warnings check box found on the Messagestab. Specifc messagescan be enabled or disabled in the list below the main checkbox-Temporarily disabling the generation of wamings may be useful during debugging to prevent messagesabout unreachable code or mriables being declared and never used.When you work on the final version of a program, it is much bener to work drough all ofthe warnings than to simply disable them. 4.5 COMPILE AND trlAKE PROIECTS Obtaining an executableprogram file requires the folowing steps: l. Compilethe project: C sourcefilesinto an assembler sourcefile. 2. Assemble the assembler sourcefile. Canpiling a f'le executes step 7 only. Marting z ßle executessteps 1 and 2 for the nain Droiect lile. 4.5.I COMPTLEA PROIECT The CodeVisionAVR C Compiler is called for a project by the ProjectlCompile File menu command, the F9 key or the Compile button of the toolbar. Execution of thc CodeVisionAVR C Compiler produces an assemblersource 6le with the .ain e;'tension. After the compilation, the Information window opens, showing the compilation results. SeeFigure 4-14. The Information window Jiststhe compiler option setrings at the top. Ne*, the statistics on the number of lines compiled and the number of errors and wamings are listed. The rest of the window details how much rnemory is used and for what purposes. Iferrors or warnings are generated during compilation, they are listed in the Messageswindow located under the editor window and in the navigator window. Double clicking the effor or warning messagehighlights the troublesome line of code. In Flgure 4-15, the frst warning was double-clicked and the associatedline ofcode is hig ighted. The Codel/isianAVRC Compilerand IDE dre.ilql]hb4FFh ri?e: lm4 byrelsl Dara Siack Lß4g 33 blite{Nj vaiablesrrea:500hto 8C0h Y6'iäbles.&e 449 brle(s) sta.karea:SClhto 10FFh 51..k sEe2623byletrl usesd0 bytelrl[0,02ol [EPB0M] Results Showing Compilation Figure 4- | 4 lnformotionWindow 4 . 5 . 2 M A K EA P R O I E C T An executablefile is cteatedby making a prcject.To nake a prolect, selectthe Project lMake menu command, press the Shift+F9 keys, or click the Make button of the toolbar. The CodeVisionAVR C Compiler executes,producing an assemblersourcefile with the .asn' extension.If the compiler generatedno errors,the Atmel A\{R assemblerAVRASM32 is automatically called, and the assemblerruns on the newly oeated assemblersourcefile. The assemblercreatesan executableprogram file in the format specifed in the C Compiler tab ofthe Configure Project dialog box (ProjectIConfrgureIC Compiler command). After the make processis completed, the Information window opens,showing the compilation results.There are two tabs in the window, Compiler and Assembler These tabs allow you to revie\ü the results ofboth the compiling and the assembLingofthe program. An example of the compilation results is shown previously in Figure 4-14. Fig:re 4-16 shows an example of the assemblerresults. The top of the Assembler tab displays the version and copyright information for the assembler.The next section in the window is the assemblerfeedback of how much memory is 221 222 Figure 4-f5 Compilotion ErrorsDisployed in Messoges Areoond,ntheNoyigator usedby the program for eacharea,including the code segment(csegor FLASH), the data segment(dsegor SRAM), and the EEPROM segment(eseg). The line below the memory usagetable is very important: 'Assembly complete with no errors."Occasionally,a program cornpilesfine but errors occur during the assembly.If this happens,a window opensand displaysa messagethat errorsoccurredduring assembly. This line in the Assemblertab of the Information window tells how many errors occurred.To find the errors,open the ./sl file and searchon the term "Error." The bottom part of the Assemblertab showsthat the iom.eepfile wzs deleted.This fi1ewas createdfor EEPROM initializations, but none existedin this program, so the file is not needed. 4.6 PROGRAM THE TARGET DEVICE The CodeVisionAVR IDE has a built-in In-System AVR Chip Programmerthat lets you easilytransferyour compiled program to the microcontrollerfor testing.The programmer Tle CodeVitiozAVRC Compilerand IDE WFA.SM: AVFm+ro asenbht 2.i .0 (b|lld38Od 1200503071421 :apyilhl If,l 19352005AIMELC(fporabon \Tm6$128nem.ryu.. .Ln|n!rylbJillll: ;.säcnl EeEihEhd CodeDäla Used Säe U!62 Z.7Z .6€91Od000@ 0x000ds3252236319ß131072 .&aelo$oümft0005e50 22s 22365535032 0 1 1 4036O& :€se9l0r00@0ür000üI \ssombb orplae 0 dc Results Figure 4-16 Assembler is designed to work with development boards such as the Atmel STK500, Kanda Systems STK200+/300, Dontronics DT006, Vogel Elektronik VTEC-ISP, and the MicroTionics AICPU and Mega2000 development boards, which are connected to your computer's paralle1printer port. The Settings lProgrammer menu item opens a window to select the tlpe of programmerto be used. The programmer is opened by selecting the Tools IChip Programmer menu command or by clicking the Chip Programmer button on the toolbar. F.rgte 4-t7 shows the chip programmer openedwith a Kanda Systemsprogrammerselected. 4 . 6 ,I C H r P The one item on the Chip Programmer dialog box that dictates what is arailable in the rest of the window is the Chip list box, which selectsthe qpe of chip you wish to program. The chip selection determines the size of the FLASH and EEPROM buffers. AIso, the chip selectiondetermineswhat is displayed-the FuseBit(s), Boot Lock Bit 0, and Boot Lock Bit 1 frames-and whether these fiames are disolaved at all. 223 224 chip: lSffi:] *,ir ctoct : fiI?Effii-ll startF- *l'rqgamAl € neercnpl vrz h End: IEE?- h srarlö- h End: lE- h llhecksun 000tlh Checksum: IFEEh ProEamming a Programmin! di$abled f sndVeritication diräbled Prograrnming BooiLockBit ölot LockBit1 lr 801=tSit2=1 a t0t=0S02=j (r 811=1 812-1 r Bil.ß 812=1 a Bü=o 812=0 Eoz-ü C 811=0 r Bü-t8ü2-0 =ü CKSELl cK5EL2=ü CKSEL3=0 SUTÜ=Ü SUTI=0 EÜDEN=! E0DLEVEL=B 8üüTFST=0 E00T5Z0=0 EüüT521=ü EESAVE=|] CKüPT=0 JTAGEN=|] OCDEN=]] b";;';=; lEPFtlM V |7 Checksiluitue F t)hecklraswel* Plessrve Figure 4-f7 :l Yeitr CodeVisionAVR ChipProgrammer 4.6.2 FLASHAND EEPROM The programmer has two memory buffers: the FLASH memory bufTer and the EEPROM memory buffer. The contents ofthese buffers are loaded and saved with the FilelLoad and FilelSave menu commands. The suDDorted file formats are as follows: . Atmel .romand.eep . lntel HEX . Binary.bin After a file is loaded into the corresponding buffer, the Start and End addressesare updated accordingly. The Checksum field is also updated with the checksum ofthe loaded file. It is possible to view and edit the contents of the FLASH and EEPROM buffers. The buffers are displayed and edited by the EditIFLASH and EdiIIEEPROM menu commands. Upon selection of one of these commands, an Edit window displaying the corresponding buffer contents opens (refer to Figure 4-18). The CodeVisianAI/RC Campilerand IDE 0025s40c 0000940c 0000940c 0000s40c 0000s40c 0000g40c 0000940c0000 tz 0000910c 006a340c 11000 940c 0053940c 0000940c0063940c 0000940c0000lt tl EIH227BBII II I]OOO 94OCOOOO O|]OO S4F827EEBBEC EFEsE1F8BDF1E1FÜEDFIEOEE s68AF7E9E080E0s4E6A093ED3701FTESE4E8E0F090059015otBF 0tF0 9730ti ll EOE4EFEEESCFöE '+ 9145S1B5$85 9195SI]0592OD9701F7E']O]FBCFFO E5EFBFED s40ü11494 S40E06EB2DAD 27BB59AD4FBEB1EC93EC94D3E0E315EDF40C2400äN 06FeSE]El40E 06EBE0E12ECE340E06F8S518940E06EB2DEgzDFgS631ZEBEll lo 2DEA2DFB36312EAE2E8FE3EA8FE2S40E0rlF8951893rrr 2466248824SS14ED.t t 429 E8E8E1F315E805F9F40CC00r CFFIr4EDF421E000E0E12E6EC00A2DEE27FFöl Eä SAsEYf 0b SSsEC0ü1CFFD SSED 4FFE810094E3E0E315EEF40C24EE2FE0C27F81E8BSEC c03324882459E1E4E0F0l58E 053FF3DC35082488249531E00176D4E3F3E49508A3 $l 248€249SStE0 0177D4DC F3E495083304E000E0009lE0 0171170EF44C24882493$t $l EtE4 E0F0158E069FF3DC5F0FCFF3C25181E8BgEF248824!S 9977C005E0E3E0F0ää ää EBEFE8E72DE765EOBgED9508E'IE] BgEDIE N 15E8O5F9FTCCB1EF962] 95OE27EEEBEE 2?EES3EO B16FD4AE93EFD4B3g]AF 2BEAÖi ,q D4B6BBET950893OAB3E27FE7BEE2EOOÜ BBEZDFCSDFE3DFC3D4A593EF91E0 0170 55E27FE091AFDAACD4B033EFD4.A251AFr3 fIA DFAE3280F424g1A0016F0S rä o4a?60E2D4ÄA93EFIlEo 017095E27FE0glAF D49EBEEB 35A3F4U9C026D49EE5E3D49F33E00r5F 914001743042F4309lA0 01783046F l 51 6l 9868DF75C00AS1A0017830460S 6t 30a7F4ß C00AD49691A0016F3543F0219A5BDFED F0113047F409D486E5E393E0016F5F0FCFD3S1E0016FCIDD931493042044F529ät 05 1 30A7F429E0EJ2E7EDF96E503C0112477 Figure ,f- l8 CodeVisionAvR Edit FLASHBuffer The buffer contents,at the highlighted address,are modified by qping in the new value. The highlighted address is modified with the arrow, Tab, Shift+Tab, PageUp, and PageDown keys. Occasionally it may be usefirl to fi1l a block of FLASH or EEPROM memory with a given value. Right-clicking in the Edit window opens the Fill Memory Block dialog box, as sho'wnin Figure 4-19. This dialog box specifiesthe Start Address, End Address, and Fill Value of the memory areato be fi11ed. The FLASH and EEPROM buffers are programmed to the chip, read from the chip, or compared against the chip through the Program, Read, and Compare menu items Figure 4- | 9 CodeVisionAVR ChipProgrammer FillMemoryNockDiologBox ZZs n6 respectively.The chip must alwap be erasedprior to prograrnming the FLASH buffer. If the ProgramlAll menu command is used, the chip erasewill automatically be performed. Ifthe chip is locked, the read and compar€ operations on the FLASH and EEPROM from the chip will not work. 4.6.3 FLASH LOCK BITS The FLASH Lock Bits frame ofthe Chip Programmer dialog box has options for selecting the security level setting for the chip- This security level must be one of the following: . No Protection---nllreadandprogramminS operations äre allowed . Programming Disabled-reädins$e FLASHandEEPROM areasis allowed, but writingto themis notallowed . Programming andVerification disabled no readintto or writingfrom eirher areais allowed. After progamming the chip is complete, regardlessofthe state ofthe lock bits, the FLASH cannot be *aitten to ag"in until a chip eraseis performed. The lock bits are automatically writren to the chip duing a ProgramlAll operation or can be written independently through the Pmgramllo& Bits menu command. The curent value ofthe lock bits is read with the ReadllockBits command. A chio erasealwavs sqs the lock bits back to no protection. 4.6.4 FUSE B|TS Ifthe chip you have selectedhas fuse bits that can be programmed, a supplementary Fuse Bit(s) frame appean. In this frame are vaious check boxes,one for €ach tuse bit available on the selectedchio. The fuses and their resDecti\,.e usesare described in the Atmel datasheets. The tuse bits are programmed to the chip and read ftom the chip using the Program lFuse Bits and ReadlFuse Bits menus. The tuse bits are also programmed as prrt of the ProgramlAll automated programming prccess. 4.6.5 BOOT LOCK BIT OAND BOOT LOCK BIT I Chips that support bootJoading applications have additional security bits that lock the boot loadersectionofmemory-The Boot Lock Bit 0 and Boot Lock Bit framesand options support these additional security bits. For information on how these bits are used, refer to the Atmel datasheets. 4.6.6 SIGNATURE Each different c1rip gpe in the Atmel AVR line has a unique signature. The ReadlChip Signature menu item reads the signaturc of the chip to determine the gpe of chip connected to the programmer Many programm€rs use the signaturc to veri4, the chip selected against the actual hardware connected before performing any operation. The different chip Tlre CadeririorAl/R C Catu?ile/ df,d IDE q?cs havc differcnt programming parameters,so unexpectedresults crn occur if the actual chip and the selectedchip qpe do not match. Howevea occasionally it is necessawto program or read a chip as another chip q?e. For e{ample, when the Atmega128 was frst released,many prcgrammeß supported it only in rts Atmega1O3 mode, so it was necessaryto ignore the signature of the Atmega128. It is lor this reasonthat a check box is provided to disable the reading ofthe signature. Ifthe signa ture is not corrcct and Check Signatue is selected,the progamming will not continue. If the Check Signatur€ check box is not selected,programming wiJl continue regardlessof the srgnaüre . 4.6.7 CHIPERASE A chip erase is autonatically performed whenever the ProgmmlAll menu command is used.To erasea chip independent ofthe programming opcration, the menu cornmand Program Erase Chip is available.The PrograrnlBlank Check menu command verifies that the chipt EEPROM and FLASH nenor,v areasare erased.This verification is also performed automatically by the ProgramlAll function unless thc Check Erasure check box is cleared. The Preserve EEPROM check box does just that it enables the preservation of thc EEPROM data through a chip erasecycle. This is accompJishedby reading the EEPROM into a buffer, performing thc chip erase,then writing the data back to the EEPROM. Ifthe chip is locked to prevcnt reading, the EEPROM is not preserved,becausethe drta could 4.6.8 PROGRAMHINGSPEED To speed up the programming process,clear the Check Erasure chcck box. In this case, there is no verification of the corecmess of the chip erase.You can also clear the Verify check box. When the Veri& checl box is cleared, there is no verification of thc correctness of the FLASH and EEPROM programming. These are usefi.rlwhen you dcbug code and program the device repeatedly for testing. When you program the chip with the flnal ver sions of codc, it is recommended that you have the Check Erasure and the Verify chcck 4,6.9 PROGRAHALL The Program All nenu command automates the programming process.This is probably the menu item that is most used in the programnel The steps taken arc as follows: L Erasethe chip. 2. FLASHandEEPROM bldk check(if check Erasure is check€d). 3. Programandverit the FLASH. 4. Programandv€rit th€ EEPROI4. 5. Programthe FuseandLockBits. 4 . 6 . IO O T H E R P R O G R A M M E R S In-system programmersthat are not direcdy supportedby CodeVisionAVR can be added to the tools list if they support command-line calls. Our examplesshow TheCableAVR in-system programmer as a stand-alone programmer, but this can also be called by CodeVisionAVR through the command line. To add a new tool, selectthe Tools lConfigure menu item. When the ConfigureTools dialog box opens,click the Add button. This opens a browser to select the executable for the tool. Fizure 4-20 shows TheCableAVR beins addedin the ConfigureTools dialog box. Once the tool is added, click the Settings button to open the Tool Settings dialog box which establishesthe settingsfor the tool: the name of the tool asyou want it to appearin the Tools menu, the path and file name for the executablefile, any command line parameters for the too1, and the working directory for the tool. Figure 4-21 shows the settings for TheCableA\4R. The command line parameter for TheCableA\rR is simply the TheCableA\rR project name (iom.isp).TheCableAVR allows you to ffeate a project containing the program files for the FLASH and EEPROM memory areas,aswell asfuse bit and lock bit settings. Severalother settings are part ofthe project file, but these particular settings depend on the target device. Once the tool is added and configured, it appearsin the Tools menu. Figure 4-22 shc;'r.ts TbeCableAVR.exelisted in the Tools menu. Simply selecting this menu item calls TheCableA\rR and programs the chip. TheCableA\rR window opens,loads the project f,le, and begins the automatic programming cycle. If an error occurs during the programming Figure 4-20 ConfigureTools DialogBox,AddButtonClicked TAe CodeVisionAVRC Con?iler and IDE Figure 4-21 DiologBox ToolSettings Figure4-22 CodeVisionAVRTools Menu cycle, TheCableAVR window remains open for the user to addressthe error (refer to Fig_ ure 4-23). If the programming is successfullycompleted, TheCableAVR closes. 4.7 CODEWIZARDAVR CODE GENERATOR When creating a new project, you are given the option of using the CodeWizardAVR to automatically generate a shell of code for your project. The CodeWizardAVR is a great tool for saving time during the startup phase of any project. It automatically generatescode to setup timers, communicationsports, I/O ports, interrupt sources,and many other features. This savesyou from having to dig through the data book for control registers and their required settings. To effectively use the CodeWizardAVR, you must know how the microcontroller is to be usedin your project and you must havea basicknowledgeofthe hardwareofthe processor. Chapter 2, "The Atmel RISC Processors," of this book covers many of the architectural features available in the Atmel AVR microcontrollers. Chapter 5, "Project Managment," details good project planning and assistsin project planning and preparationfor writing software. For now, carefu11yconsider which I/O pins are used as inputs or outputs, what 229 230 Iils eameütiin qe!;cE lelp fhles Fr!$änYffid: 0 FL45H SUE] fEFRüM SA€: |LASHtllUM: €EPBüM [5U]v1: -&""'l 13:l7Z dK IXSSüF $lBr:F Er€ie 0z s'** I rl,i I 5;-a rTu--__l EEFF0V tr"" I lir*lr'"+.,irrh.iEaq:Errb*--F ir- e,"-"" i Edit l] ------t*rsli=ll *' s'",,"c,'"'.,J I r"""""i'" Figure 4-23 -t i lri r'u*"r ] ent!!::k l -l 'i'' r TheCobleAVR Softwore baud ratesarc requiredbv the communicationports,what timers are required,and what interruptsourccsareneeded. The CodeWizardAVR placesthe generatedcodedirectly in the sourcefi1eyou speciSrThis is the starting point for your program. Sinceyou will be editing this fi1e,any of the settings can be modified later,but 1.ouwill haveto look up the new scttingsin the datashectsfor the mlcroploccssor. Thc featuresavailablethrough the CodeWizardAVR dependupon the microcontroller sc lccted and the version of CodcVisioru{VR in use.(Rememberthat the e\.aluationand lite versionsof CodeVisionAVR do not support all of the Atmcl AVR processorsand do not support the san.refeaturcs in the CodcWizardAVR as the star.rdardversion. Refer to http.//urou.hpinfotech.rofor information on eachversion.)Figure 4-24 shows the tabbed framesofoptions availablefor the NlTiny22 in the standardversion of CodeVisionAVR. The Atmegal6 sl.rownin Figure 4-25 has many morc tabbedframesavailable. This section uscsthe Atn.regal6 as the targct deviceand covcrssome of its basic options availablein tl.restandardversionof CodeVisionAVR.The examplccode{ragments provided in this sectionare specificto thc Atmegal6 dcvice.The initialization codegeneratedby rhe CodeWizardAVR is placcd at the top of nain). The intcrrupt routines are placed above nain0. The CodeVisionAVRC Compilerand IDE Figure 4-24 ATTiny22Options CodeWizordAVR Figure 4-25 Atmego I 6 Options CodewizordAvR 231 232 Nate: The CodevizardAI/R i eonstunq bäflg a?datedand eryanded.Tl);s tection ;s not neant to bean ercbaustive ex/anatkn of;ßjaat resald ?ossibilities,but rather an ol)ero;eu af the turrent ca?abilitiesoftl;s taal. 4 . 7 . I C H I PT A B The Chip tab is the 6rst tab selectedas the CodeWizardÄVR window opens.The Chip list box sets the target device. Changing ofthe selection in this list box updlatesthe rest of the window. The Clock frequency in megahertz is either selectedwith tbi up and down atow buttons or entered direcdy in the edit feld. Selecting the correct frequency is very important for getting the other time-sensitive smings cofiect. At the boftom ofthe Chip tab, the Check Reset Source check box enablescode to check the reset source. Ifthis is selected the following code is generated.This code allolus the program to take certain actions depending on the sourceofthe last reset.This code is placed at the very begsnning of nainj. // if t Reset Source checkids (McucsR & 1) // Po$er-on Rese! MCUCSR&=oxE0; else if (McUcsR & 2) { // Exreroal Reset MCüCSR&=0xE0; // Ptace your code here ] eLse if (McUcsR & 4) I // Brown out Reset MCUCSR&=0x80; // P1ace your coale here ) e l s e i f ( M C U c s R& 8 ) { // watchdog ReseE MCUCSR&=0x80, // Place your code here ] else if ( M C U C S R& 0 x 1 0 ) The CodeVisionAVRC Compilerand IDE / / JrAc Reseh MCUCSR&=0xE0; code / / Place your here ]; Below the Check Reset Source check box is the ProgramType list box. This selectsbetween generating a boot loader gpe of program and a normal application. For this example, the application qpe program is used. 4.7.2 PORTSTAB The Atmegal6 has four I/O ports: A, B, C, and D. In Figure 4-26, Port A is selected.For each pin in Port A, two options are available,data direction and pullup/output value. These settings do two things. First, the Data Direction settings determine the value of the DDRx registers (DDRA for PORTA) and control whether each pin is an input or an output. Second, the Pullup/Output Value setting is used to establish the initial value for the port. Ifthe pins are inputs, the Pu11up/Output Value enablesor disables the internal pull-up resistors. If the pins are outputs, this setting determines the initial value output on the port. If, for example, we use the upper half of PORIA for input with pull-up resistors enabled and the lower half of PORIA for output with the value OxOAas an initial value, the Ports tab settings appear as in Figure 4-26. Figure 4-26 CodeWizordAVR Atmega I6 PorsTab 233 234 Figure4-27 ExtemallRQTob The generated initialization code for PORIA appearsasfollows: // Input/Oubput // Pot|- A PORTA=0xFA, DDRA=0x0F; Ports ini t ial i za Li on 4.7.3 EXTERNAL IRQ TAB The External IRQtab has two check boxes that enable or disable the external interrupts: INTO and INTI. If the intemrpt is enabled,then the Mode list box appearsand determines what conditions causethe interrupt. For example,INT0 is enabled and is set to interrupt on the falling edge ofthe signal, as shown in Figure 4-27. The following interrupt routine is added to the sourcefile: // External Interrupt 0 service routine i n t e r r u p t L E X T _ I N T 0 vl o i d e x t _ i n t 0 _ i s r ( v o i d ) t / / Place your code here ) The code generated to enable INT0 intemrpt on the falling edge is added to main) and aPPearsas // // External Interrupt INTo: On INTo Mode: Falling // // INT1: Off // aNT2: Off GICRI=0x40' MCUCR:0x02; MCUCSR=0x00; GIFR=0x40; (s ) iniEialization Edge The CodeVisionATRC Com2ilerand IDE Figure,f-28 TimersTob ,1.7.4 TIMERSTAB The Timers tab, sholrn in Figure €28, is a very versatile tool. It coversTimer 0 through Timer 2 setupsand the Watchdog timer setup. For this example,Timer 0 is set up to use the System Clock asits clock sourceand t o n at 750 WIz When the timer rolls over, an IRQ is generated.The code wizard outputs both the interrupt routine and the code to initialize Timer 0. The generated initialization code follows: // // // Timer/counter Clock source: 0 ini t ial i zat ion System Clock 750.000 kHz Clock value: l4od,e: Normal top=FFh Disconnected / / . oc0 output: T C C R 0= 0 x 0 2 t T C N T 0= 0 x 0 0 t // OCR0=0x00; A shell for the interrupt routine ca11ed when the timer overflows is placed above main): // Tirner interrupt routine interrupt service v o i d t i m e r o _ o v f _ i s r ( v oid) ITIMo_OVF] 0 overflow / / Pl"ace your code here 4.7.5 USART TAB The USART tab has many options once the Receiver and./orTiansmitter check boxes are selected,For eachofthese check boxes,there is an option to make the receiver or transmitter interrupt driven and a place to speciSrthe length öf the associateddata buffer. When the CodeWizardAVR generates intemrpt-driven USART routines, the standard 7/O k&zry rortines putchar) andgexhar) ate rcplacedwith the codegeneratedir1the sourcefile. This allwrs thepuxhar) and,gexhm) frnclions to be interrupt driven. This in turn makesall of the functions that useputcbmQ ar'dgxcharQ, s:ucJr. aspri.ntf) andsmnf), interrupt driven aswell. Below the transmitter setup fields is the USART Baud rate list box, with many of the common baud rates available.The actual baud rates available depend upon the ftequenry of the clock used to drive the device.The CodeWizardAVR displays the error percentageassociatedwith the selectedbaud rate and the.systemclock In this arample, shown inFigarc 4-29, a baud rate of9600 is chosen,and the baud rate error is 0.270.This error percentageis small enough not to affect communication with other devices. The Communications Parameters list box is the final field on the USART tab. Select the desired setting, and the CodeWizardA\rR generatesthe needed initialization code for the Figure 4-29 U$ARfIab The CodeVisionAVR C Campiler and IDE USART to achievethose settings.In Figure 4-29, the settingsare chosenas 8 data bits, 1 stop bit, and no pariry Interrupt-driven codegeneratedfor the USART is placedat the top of the sourcefile. No modifications to this code should be necessaryfor the use of the standardI/O library routines. (This code is not listed here becauseit is lengthy.SeeFigure 4-34.) The initialization codeplacedin mainl for the USART settingsin Figure 4-29 is asfollows: // // zA!'O"l U5AK1 rnrE a communication Parameters: USART Receiver: On USAP'l Transmi Eter : Or // USARl // tqooe: ASVnCnTOnOU // USART Baud rate: UCSRA=0x00; U C S R B =0 x D 8 ; UCSRC=0x86; U B R R H =0 x 0 0 ; U B R R L =0 x 2 6 ; B Data, I stop, No Parity S 9600 4.7.6 ADC TAB The ADC (analog-to-digital converter)tab allows you to generatecode to initialize the ADC. Ifthe ADC Interrupt checkbox is selected,a shell is generatedfor the interrupt routine calledat the completion ofthe conversion.The Volt. Ref. list box selectsthe reference voltagefor the converter.The final field is the ADC Clock list box, which determinesthe prescalersetting for the conyerter.The prescaleris set up to divide down the systemclock to reachthe selectedfrequency.Figure 4-30 showsa simple setupfor the ADC. File Help l2c I t wi'* | 2wirefl2xl LCD I Eireanged lnfomatian I Ptoiect f,hiF lPorts I EnternallFü l Timers A0f, lSPl USART I AnalqComparBtor bits 17 ADCElöbledT LJseB l !nrErrup( ,AutcTrigger Source: lffi;-------*---l Figure4-30 ÄDClob 237 238 The codewizard generatesthe following codeto initialize the ADC andto readraluesfrom it accordingto the seningsin Figure 4 30: // ADC inltialization // aDC Clock frequency: 187.500 kHz aDc vol rdg. Referpnce: Avcc pin i^âr s.' r.a None ADMUX=ADC_vREF_TYPE, ADCSRÄ=0x85; // Read the AD conversion resulE .rs grFd inr read .clclunsiqned chdr dd._inpur I t ADMUX=AdCiNPUT IADC VREF,TYPE; // Starr the AD cooversion ADcsRAl=0x40; 'waic to! rhe AD conve sion io.orp F e w h i l e ( ( A D C S R A& 0 x 1 0 ) = = 0 ) ; A D C S RlA= 0 x 1 0 ; leturn ADCW; ] 4.7.7 PROJECT tNFORI'iAT|ON TAB The Project Information tab is just thaq it allows you to enter project informxtion and th€n formats it into the genemted source file along with information about the setup of the project. Figure 4-31 shows the project information entered for the example project. An example ofthe addition to the source frle for the project infotmatior This proqlan was produceal by the CodewizaldAVR V1.24 . ?d Professional Autona!ic P!olrran Generator @ copyli9rhE 1998 2005 Pavel Eaialuc, EP hfoT'ecb hllp: / /]'w. hpinfotech. con 4 Exanple Projecl : chapEer Dale AuLhor Company | L2/74/2005 : Sa11y : Sa1ly's Source Project code tab follows: s.r'1. The CodeTisionAlrRC Comriler and IDE Cl-ock frequency Memory model SRAM size Externat size S t a c k Data Figure 4-3 | : 6.000000 MHz : sma11 :0 : 256 ProiealnformotionTab 4 . 7 . 8 G E N E R A T ES O U R C EC O D E once the codewizardA\rR options ale set for the pfoject, the codewizardA\rR is ready (refer to to generate a source fi1e. Selict the FilelGenerate, Save and Exit menu item f rErfie +-52). Tii, oo"rr. severalbrowser windows to select the name of the source file, the r-rameof the projecifile, and the name ofthe code wizard file. Once the appropriate file names are eni#d, the project is created and opened. CodeVisionAVR then appearssomewhat asin Fig*" n-f S. i'igltt" +:4 lists the sourcecode file that is createdwith the settings in the previous Dartsofthis section. 239 240 Figure 4-32 FilelGenerote, Soveond ExitMenu ltem r Eö*:1"* ' fi -hF& Figure ,L33 NewPrcjectCreotedby the CodeWizordAVR Tb. CodclitionAYR C aaa?ilpt and IDL sas produced by Ehe This prosran Professional Codei,lizardAVR v1.24.7d Automatic Piogran Genelatsor 1998 2005 Pavel Hai(Iuc, @ Copyrlght http: / /wN. hpinfotech. con e-nai1 : of f ice@hpinf oEech-con 4 Exanple Project : Cbaprer Daie Aulhor Conpany :72/14/2405 : sa11y : sa1ly's soulce aTneqal6 chip Example EP InfoT'ech s.r.t, Project Coate Project : aTnegal6 type Clock frequency Memory nöde1 External SRÄM size Data stack size : 6.000000 MHz : Sna1l : 0 . 256 ******,*,,+'',''' < m e 9 r a 1 -6h > +include 0 selvice rouEine // External Intedupb intserrupt IExT INToI void exE,inEo_isr (void) { // PLace your code here J +define TXBB 0 +define UDRE 5 +dEf iNC +define +define +dEfiNE +define F R A M I N G _ E R R O (R1 < < F E ) P A R T T Y _ E R R o R( 1 < < u P E ) DATA oVERRüN{1<<ovR) D A T A R E G I S T E RE M P T Y ( 1 < < U D R E ) R x C o M P L E T E( 1 < < R X C ) Figure 4-34 Soutß CodeCrcatßdby drc GdeWtzadAVR ((nltinues) / Al 242 // USART Receiwer char rx_buffer buffer IRX_BUFFER SIZE]; +if RX_BUFFER_SIZE<256 unsigned char rx_wr_index, unsigned // bit inc rx wr_inalex? rx rat lndex,rx rx_ral_index. This flas is sets oD üSART Receiwer rx_buf f er_owerf 1os; interrupt // USART Receiwei interrupt IUSART Rxc] void service usart rx counter; rx counter; buffer overflow routine isr(voial) { cha! slatus, data,. if ((status & ( F R A M I N G _ E R R O IR P A R I T Y E R R o R I D A T A _ o V E R R u N) =) = O ) t rx buffei lrx wr_indexl =daEa. l f ( + + r x w r i n d e x = = R X _ B U F F E RS r z E ) r x w r i n d e x = o , . if {++rx counter == RX_BUFFER_SIZa) rx_countser=0; rx_buf fer overf tos=1,. \J Jt J +ifndef DEBUG TERMINAL_IO_ fron the USARI'Receiwer buffer // Get a chalacter +defi4e _ALTERNATE GETCHAR I while (rx coünter==o); data=rx buffe. Iix_rd_index] ; ( + + r x r d i n d e x = = R X _ B O F F E RS r z E ) r x r a l i n d e x = o ; if ) Figure 4-34 SourceCode Crcotedhy the CodeWiza'dAVR(Continues) Tbe CoderiiotAt TX_BUFFER SrZE +define 16 TX,BUFFER SIZE<256 +if unsigned char lx wr index, unsiqned inL tx R C canqilel ahd IDE tx rd rd wr-index,tx inalex, tsx-coDnter; index, tx-counter; service .outine intserrupt // USART Tlansnitter ü s a r t t a i s ! ( v oid) T x c ] v o i d intexlup! [UsaRT { if (Ex_counter) tx_counter; UDR=Lx buf f e! [ Ex-ral-inalex] ; == Tx BUFFER-SIZE) tx if (++tx rd,index rd-index=o; )t ) +i fndef _DEBUG TERMINAL-Io// Wri-Le a chaf,actser to the +def ine _ALTERNATE_PUTCIIAR void putcha!{char while (tx-countei if (rx_counter Ex_buffer if {++tx buffe! USART TraDsnitter c) == Tx BUFFER-SIZE); ll ttucsra * DATA REGrSa0ER-EüPTY ) ==0 ) ) =c; I rx wr-index] w! index == Tx BTJFFER-SIZE) tx wr index=ot ] +endi f // Standard InpuE/Output #include <stdlo.h> funclions service toutine 0 owerfloo inlerrupt [TrMo ovF] void tinero ovf-isr{voial) Sour.e CodeGeotd by the CodeWEadAvR (Connnues) Figure /L34 // Time! inlelrup! 243 244 { ) +def ine aDc_vREF_TYpE0x40 // Read the AD conwersion result unsiqned int reaat adc{unsiqned char adc input) ADMUX=adc_inpu. I ADC.VREF TYPE, the AD conversion // start fot the aD conwersion // wait ( (aDcsRA e 0x10)==0); white to conplete ADcSRA J=ox1o; I Declare // void your variattles s1obal here nain(voial) you. // Dectare // ReseE Source if (McucsR& 1) t locat wariables here checking // Power-on Reset MCUCSR&=0x80, I else if { (lttcucsR& 2) // Exteraal Reset MCUCSR&=0x80; // Place your code ] else if here (McUcsR5. 4) t // Brown out Reset MCUCSR&=oxE0; // Place your code here I FiAur€ ,{-34 SourceCode C@trd lry the CtdewizotdAvR (Coninues) Tbe CoderniorArR else if C Con?ilel and IDE ( M C U C S R& 8 ) t // walchdog Reset MCUCSR&=0x80; // Place youx code here l e t s e i f ( M c u c s R& 0 a 1 0 ) { // ,]TAG Reset MCUCSR&=0xE0; // Place your code hele ]; // // // rnput/ourpuE Po.ts ioiLializatlon Porr A inirialization Func?=In Func6=In Func5=In Func4=In Func3=oua Func2=Out Funcl=out // s l a t e ? = P s t a t e 6 = P s t a t s e 5 = Ps t a t e 4 = P S t a l e 3 = 1 S t a t e 2 - 0 S e a E e l = 1 // // Poft B inirialization Func?=In Func6=In Func5=In Func4=In Func3=In Func2-In // sEaEeT=r StaLe6=1' Slate5=T State4=T Staie3=T Funcl=In SLate2=1' SealeL=T DDRB=0x0 t // // Port c inirialization Fnacl=h Func6=In Func5=In Func4=In Func3=In Func2=In Funcl=In // state7-'l state6=T staie5=1 statse4=T state3=1' Statse2=1' Statel=T D D R C = 0 x0 t // Port D initializaEion / / E D n c T= I n F u n c 6 = f ! F u n c 5 = I n F u n c 4 = I n F u l c l = I n // s.late7 ='I slatse6=T states=T Figure 4-34 Sta!e4=1' Stätef=1' Func2=In Funcl=In Stahe2=T Statel;T SourceCode CrcotEdby drc CodewzordAvR (continues) 245 246 // Tiner/counter // c10ck walue: 0 initializaEion 750.000 kHz TCCR0-0x02; TCNT0=0400; ocR0=0x00; // // // // // // // // // Tiner/counre! 1 iniEializaEion clock source: Syst€n clock Tiner 1 stopped Clock value: top=FFFFh Mode: Nornal Discon. 0C1a output: Discod. OClB ourput: Noise canceler: off Input capture on Falling Edge Tiner 1 overflow InLerrup!: Off // // Compare A Match Compare B Match Interrupt: Interrupt: off off TCCRlB=0400; TCNTlH=0x00; TCNTlL=0x00; IcRIH=0x00; IcRIL=0x00; // // // clock cLock Mode: source: value: Nornat 2 ini ridlizdrion syscen Clock Timer 2 Stopped Eop=FFh T C C R 2 = 0 x 00 ; T C N T 2 = 0 x 00 ; // External Inter.upt(s) // // // INTo Mode: INT1: Of f 11112: Off Fatting ini tializaEion Ealge cIcRI =0x40; Figure 4-34 (Continues) SoufteCodeCreakdby the CodeWtmldAVR Tbe codcri!io",|r.R C Cob?ilet afld IDE MCUCR=0x02; MCUCSR=0x00; eIFR=0x40; / / r i m e ! ( s ) / c o u n t e . ( s ) rnreffupr(s) TIMSK=0x01; // // // // // // USART initiatlzation comunication Paramelels: USART Receive!: On on USART Transmitter: USART Mode: asynchronous 9600 USART Baud rate: I initializaEion Datsa, 1 Stop, No Parity UCSRC=0x86; UBRRH=0x00; U B R R L = 0 x 26 ; // AnaLos Conparator Conparato. // Alalos ACSR=0x80; initialization Input capture by Tine!/Counter 1: Off // aDc lnitializarion treäuency: 187.500 kxz // aDc clock AVCC pin Reference: // ADC Votraqe None Source: // ADC AuEo Trisser ADMUX-ADC-VREF_TYPE, ADCSRA=0x85; // cLobal enabte inceüupts i ) Figure 4-34 4.8 sout.eCodeCrcoftdry ürc codewlzatdAy[((nltinued) TERMINAL IOOL The terminaltool is intendedfor debuggingembeddedsystems,which employserialcommunication (RS-232, RS-422, RS-485)-The ToolslTenninal menu command or the Terminal button on the toolbaropensthe Terminalwindow,asshownin Figure 4-35. 247 248 nt Figure 4-35 CodeVisionAVRTerminol Window The receivedcharactersare displayedin the main body ofthe Terminal window in ASCII or hexadecimalformat. The displaymode ofthese charactersis toggled by the Hex/ASCII button. The received charactersare savedto a file with the Rx File button. Any charactersqped in the Terminal window are transmitted through the PC serial port. The characters entered can be deleted by the Backspace key. Clicking the Send button causesthe Terminal to transmit a character whose hexadecimal ASCII code value is specified in the Hex Code edit box. A file is transmitted by clicking the Tx File button and selecting the appropriate file. Clicking the Reset Chip button resetsthe AVR chip on a STK200+/300, VTEC-ISR DT006, ATCPU, Mega2000, or other similar developmentboard. At the bottom of the Terminal window, a status bar displays the following: . SelectedPC communication port . CommunicationDarameters . Handshaking mode . Received charactersdisplaymode . Typeof emulatedterminal . Stateofthe transmittedcharactersechosefting The CadeVisionAVR C Conpiler and IDE Port: Böudratei Dötdbits: I lDrMr lr**-: F----"r Slopbit*: fi**l Förity: l'*-: r:::'-'--'-'--t Emulation:l | y Sone Xdn/XDff RTS/CT5 DTB/05fr ApperdLFl* 0n Rgeeption f -j r J ffi:l Figure 4-36 Flows: ll$lumns: Fonl: w wa *l lcno ll Eun"a | ? l:q I DiologBox Settings CodeVisionAVRTerminol The settingsfor the Terminal window are modified by the SettingslTerminal menu item. The Terminal Settingsdialog box is shown in Figure 4-36. The Terminal window must be closedbeforeyou modifl' the settings.The current settingsare shown in the bottom status bar on the Terminal window. 4.9 THE ATMEL AVR STUDIO DEBUGGER Both softwaresimulatorsand in-circuit-emulatorsareusefulfor debuggingsoftwareand are Most include some method of starting, stopping, and sometimesreferred to as debuggers. steppingthrough a program. Most alsoallow the user to peek at and evenmodiS' registers and variablevalues.They are invaluablein helping you find out why your program is not operatingasyou expectit to. CodeVisionA\rR is designedto work in conjunctionwith a particulardebugger,the Atmel AVR Studio debuggerversion4.06 or later.AVR Studio is a softwaresimulatorfor Atmel's AVR parts.AVR Studio alsosupportsin-circuit emulatorssuchasAtmel's ICE 200' ICE 50, andJTAG ICE. AVR Studio is availablefree from Atmel'sWeb sitezt http://ztxrau.atmelconT/. While it is beyondthe scopeofthis book to go into greatdetail about the operationofAVR Studio,there are somebasicoperationsthat areusefulto everyprogrammer:loading a C file for debugging;starting, stopping, and stepping through a program; setting and clearing breakpoints;and viewing and modifying variablesand machinestate.You are encouragedto utilize the help files included with AVR Studio for more advancedoperations. Debuggersalso usually require speciallyformatted files. These files contain information aboutthe format ofthe C file, variablenames,function names,and other suchinformation' The files used by AVR Studio are denoted with a.ro,f extension. CodeVisionAVR is designedto createthis qpe offile and to launch AVR Studio from a toolbar button. 250 4.9.I CREATEA COFF FILE FORAYR STUDIO A COFFfile is required to perform C source-lcvcl debugging in AVR Studio. To crente thrs qpe of 61e in CodeVisionAVR, select the ProjectlConfigure menu item to open the Confgure Project diafog box. Select the C Compiler tab; in the lower right corner is the File Ougut Format(s) list box. Sclcct the COFf, ROIvl, HEX, EEP list item. Click OK to close the windorv and savethe sctting. 4.9.2 LAUNCH AVR STUDIO FROM CODEVISIONAVR CodeVision-{\rR has two methods for launching a debugger appJication, .r menLritem and r toolbar command button. Before using either method, hower€r, you need to speciF,'the prth to the debugger To do this, sclect the SettingslDebugger menu item and click the Browse command bufton in thc windorv that appears.Brorvse to the debugger and selectir. The default path for A\ß. Studio is C : \Progran Files\Ainel\AvR Tools\av.Studio4\ÄvRstudio. exe I{owever, it might be placed differendy in 1'our rystcm. You can perlorm a search for AI/RS/udio.eH to locate the flle if necessary.Oncc thc file is selected, simply use dre Tools lDebugger menu item, the command button in the toolbar with the bug icon, or the ke1-sShift+F3 to launch the application from CodcVisionÄVR. 4 . 9 . 3 O P E NA F I L EF O R D E B U G A\rI{ Studio refers to the debugger sourcefilcs as Objett Fiks.To open the .ra/frle createdby CodeVisionAVR for debugging, selectthe FilelOpen Objectfle menu item and browse to your 6le. Select 1'our .ra/6le and click OK. This opens the Select Device and Debug Pl'rtform dialog box. In the left column, sclcct the platforn -rcu are using as your debugging platform (this example uses the simulator). In the right column, select the device you re simulating or emulating (this examplc usesthe Atmegal6). Click Finish to close the di:log box and open the debuggcr rv;ndorv. As thc program opens, it is displ4,ed as C code with thc dcbugger active. The Run bunon i in the upper right part of the tool bars and appcars as a page of tert with m alrow nning down the right side ofit. The Stop buton is located to the right ofthe Run button and appearsasr'pause" button (two venicalbars).The Debug menu cannlsobe usedto run and break the progran. Ye11owaffows appear in thc lcft margin of the code windows when the program breaks; these denote wherc the code execution hatted when Break was clicked. Whcn the sourcelile clanges, becauseI'oLrfound rvhat was rvrong and flred it, 1rcuneed to reload the debugger 61e.Usuall1,,AVR Studio detccts when this happens and prompts you to reload the file. Follou'the prompts, or simplv rc open the flle using the File menu. 4.9.4 START,STOBAND STEP Before we divc into this very inportant debugger topic, we nced to rcview one point about A\rR Studio: It has two modes, editing arld debugging. Undcr thc Debug menu arc nvo items that tell which mode vou are in, Start Debugging and Stop Debugging. Only one of The Codettiio,r|r'R C can?iler and IDE these items is available at a time. If Start Debugging is alailable {not disabLed'grayed out), ;n it 10 encerdebuggingmode.lf Shrr Debugging is disabled.tlren pu are already seLecc in you are oi the debugging menu options are arailable unless debugging mode. NÄ debugging mode. The buttons to start (run), stop, and step the debugger are locared in the upper rigit-corner ofAVR Studiot toolban. The buttons show their function when your mouse ls held over them for a moment. Equiwlent commands are also arailable from the Debug nenu The available commands are run, stop, reset, show no.t statement' step into' step over, steP out of, run to cursor, and autostep.Many ofthese are intuitive, but we should review their tunc tionaliry Table 4-1 provides a quick guide as to their respectiveuses' Run of the prcgm. The prcgm Stdts o. r€sum6 ftotion will be *cutcd mtil the uer stol6 it or a break point Brcak oi the prcsrm.When aeo SbDs or bruls Mnon üo; n hdted, aI infom,rion In;x wiDdo4 is uldaRd Re"er,Lhcdmtion t rger. r cumndy qecurin&.Lhe in s()rre od€ mode. prosm is h,lted.If müting üe DroFm nn5 unt the fi^t some statemüt-ß enc,iu"i.ad. (Tt'. .t"nw code is dNted ) dunter Ctrl+F5 Shifr+I5 (Nond Sh@Nst Sds the rlow mükd at tle &tu,l prcglu location md fooses the wid@. StepInto If in disssdbly mode, one line ofdsembler is 4@je'1. If in sose code node, one line of sore is d@ted F11 StepOver Exe@tesone instructior Ifthe instruinon is a tunction catl,the Anction is decurcd s we[ beforehalting. Exeuts insüutions u il rhe {rlrcnt fudion is coDpleteo. a breaigoht is e"-ullI4- F10 Exe@F" ißrruction' uodl the progm h* reached tt'e instnrtion indimted by the (cor in dE eurce file. Excutes instructioß one at a tine until a bftalQoint ß The cnountercd or the us is$es a bEak olmmd. insmtclioß is det@ined in the Debug dday bet@ is üpdated Opions menu. All infornariotr h al*indoß Ctrl+I10 StepOut Of Tabfe 4-f Sbift+F11 (None) Debugge.Connond Budons 4.9.5 SETAND CLEAR BREAKPOINTS A very usefirl tool in most debuggersis the abilig to set and de?r brcakPoints These.are points in your program where you want alecution to halt. Once it is halted, you can review or yoo .un choo"" to start single-stepping the progrnm to deter.'t t.gt.,.i"At.r, ".r;rft mine exactly what it is doing. 251 252 To sct or clear breakpoints in AVR Studiq right-click on the desired line of sourcecode. A shortcut mcnu appearswith the optior ofToggle Brealgoint. Select Toggle Brealgoint, and a large red dot either appearsor disappearsin the lcft margin of the code window. Once the breakpoints arc set, run your program as usual.The program halts before execut ing the selectedline. After the program is halted, aI oftlrc information in all ofthe windows is updated. 4.9.6 VIE\^,AND HODIFY REGISTERS AND YARIABLES In the View menu are listed the items Watch, Memory Window, and Register. These menu items bring up windows to display variables, various parrs of memory and registers, respectively.The information in these windo*s is not updated while the program is running. Once progarn ercution is halted, by either a breakpoint or the user commandins " brea\ the information in all ofthe windo*s is updated. The Watch window defaults to appeaing in the lower right corner.To add or remove irems, you can either right dick in the window and utilize the shoncut mcnu or double click on an empry Name 6eld and gpe in the name ofthe variable you want to watch. To change the value of the larinble, double-click the Value column and type in the new value. The Memory window overlal's the other active windows and allows you to view various memory spaces,including EEPROM, Data, VO, Program, and Register Here, you can directly watch memory being modifed. Double-dicking a value allows you to enter a new value, and thc Address box at the top allows you to specil, the addressofthc spaceyou wnnt Registers 0 through 31 can be viewed in many ways. To simply see them all displayed at once, selectthe ViewlRegisters menu itcm. Double clicting a particular register allows,vou to modify its value. 4.9.7 VIEWAND ]'IODIFYTHE MACHINE STATE Sometimes it is very useft:l to look at the exact state of the microprocessor.What are the counters doing? Where is th€ stacL pointer? V\4rat is going on lvith the I/O? Along the left side of the AVR Studio screenis a Workspace frame. Along the bottom of this frame are thrce tabs: Project, VO, and Info. The I/O tab givcs us the capability of looking ar the machine state and nodi{.ing it. There are scvcral items listed with a + to the left. Clicking thc + cxpands the list. Ex panding thc Processor item presents us with the program countcr, the stack pointer, the cycle counter, thc X, Y, and Z registers, and some other useftl tidbits ofinformation. Ex panding the I/O item presentsus with a list ofrhe feaniresofthe micrcprccessotsuch as the state of the I/O pon, the USART, the SPI, the timer, and so on. For each ofthese, thc state is sho*n as well as the associat€dcontol registers. Now you can really sec what s happening. The port C, pin 2 is low even though you are driving it high? Did you Tbe caderiiok,4I/R c Com?;let dnll IDE rcm€mber to set the pin as an outPutl Your timer is not generating interruPts-is runningi it even As with the other views into the processor'sstate and memory these windows are nol updated while the debugger is executing the program. Once the debugger halts, the information in thesewindows is updated. 4.I O GHAPTER SUMMARY This chapter has covered rnany of the features of the CodeVisionAVR C Compiler and integrated development environrnent (IDE). The IDE controls the projects and has a Powerful code editor. The IDE gives you accessto the compiler, the assembler,ard their associated options. It also provides tools such as the chip programmer, CodeWizardAVR, and the terminal tool. You should now be able to createprojects in CodeVisionAV\ add sourceiles to them, and make them into executablefrles. With the proper programming cable, you should also be able to program a target device with the built-in chip programmer You should understand the basic operation ofthe CodeWizardA\'R code generator and the terminal tool available in CodeVisionÄ\.R. Finally, we covered a few basics ofthe AVR Studio debugger,but we barely scratched the surface of the capabilities of this tool. You should now be familiar with loading, starting stopping, and stepping a program i:r AVR Studio. Also, you should be familiar with secing and clearing breakpoints ard viewing and modifying wriables and registers. You are encouragedto dormload this free program from Atnel use the help files Provided with it, and 4.1 | EXERCISES listthe source 4-Szwhat is the Proiectname?Also L Forthe projectshownin FiSure proiect (Sectjon a3). for the file names 2. In the compileroptions,whatq,peof memo.ymodelshouldbe usedfor oPtimum 4 4)? codespeedandsize?whenshouldthe oüer memorymodelbe used(S€ction alt€ra comPile aredisPlayed 3. Namethe two placeserror andwaminSmessages (Section4.s). 4. Describetie difierencebetweencompilinga proi€ct andmakinga Project(Section4.5). for PORTBif the CodewizardAvR codeSenerated 5. Fillin the blanksfor the initiälizätion Pons tab appearsasin Figur€a 38 (Section4.4. // Input/output // PORT B IORTB = 0x = 0x3E Ports Initialization 253 254 er|t.e dE lcD-Los, lm:igrd .h* !y!.rr; b:D p.tt t/tt tbE // .t // ,,cD sE Dott- // bitwis. // 'ßtidb7.. ä.d ür_hal I lwidl tbe tcD-col; 7a1t4 i3 }all op.Ez.i43 it * .ely .ra.r] tl: tä. tear7 pdlt.&.der :E s?i to at üh. Fe.ü- :: : €id (' rrgD sHrDar d- t-!cr :, rs); 1CD_DoAI = !cD_st{tDoü, LCD_5HI,oI l= 1[Cr_r); Figure 4-37 ProjectName? Figure 4-38 CodeWizordAVR PortsTob /, @zxing tre Tle codelti';o,ArR 4. I2 C C|m?iler dkd IDE ACTIVITTES LABORATORY | . Creae a new project by usingthe cod€Wizard^VR to Senerätethe sour€ecode proi€ctshouldbe configured asfollows: shell.The . USART:9600 baud,I data bits, I stop bit, no Parit)':transmit and r€c€ive€nabled . PORTA:AII inputswith pull-upstum€don . PORTC:AIIoutp'rts . Timer l: Causean interruptto occurevery5 ms 2. Modit the project g€neratedin Activity I to s€ndthe valuePr€s€ntat PORTAto the USARTonce per s€cond.Do not sendth€ valuefrom an interruPt routine. 3. Useth€ terminal tool availablein CodeVsionAVRto readthe datareadfrom PORTA in th€ proSramin Activity 2 in hexadecimalnotation. 4. Senddata ir hexadecimalnotation,f.om the terminal tool to the target device Place the valuereceiv€dby the USARTon the targ€t deviceon PORTC.V€rit that the correct valueis Dresentat PORTC. to Senerate a shelltoturn on an LEDwhena fallinSedge 5. Us€the CodeWzardAVR occurs on extemal inter.uPt 0 andto tum it off when a risingedgeoccurs on externäl interrupt | . Completeändtest the Progmm. 2ss Project Development 5.1 oBlEcTtvEs The sole o\ective of this chapter is for the student (you) to be able to develop electronic projects that invoh.e microcontollen for either commercial or pcrsonal purposes. 5.2 INTRODUCTION Electronic products involr.ing microcontrollers are most efficiendy developed using an orderly approach to the ?roce$, using a progrcssion of steps, from conception through accompJishment,that virtually always results in success.In this chapter, the processwill be desaibed and thcn applied to a real project to further demonstrate how the Drocessworks. 5.3 CONCEPT DEVELOPMENT PHASE Every project is basedon an idea or concept,which cones from any need---omebody "wants one." The need may be to fiIl a gap in a product market, to improve a pro duction process,to meet a courserequirernent, or sirnply to createsornething that has not bcen createdbefore. Becauseprojects are often started to satisE/a need, the oiginal descriptionof the project is sometimescalled a problem statementor a need 5.4 PROIECT DEVELOPMENT PROCESS STEPS The stepsyou should folow in the processof d€veloping a project are as follows: l. Definitionphase 2. Designphase 3. T€stdefinitionphase 4. Buildand test the prototype hardwärephase ?57 254 5. System integration änd softMre d€velopment phase 6. SYstemtest Dhase 7. Celebrationphde 5,4.I DEFINITION PHASE Defining the project has the objective ofclearly stating what thc project is to accomplish. This step invoh.es specif,ing what the device is to do, researching to asccrtain that the projthat f. ly dcscribe the fonction of ect is, in fact, feasiblc, der.eloping a list ofspecifcations the project, and, in a commercial environment, providing a formal proposal to go ahead wirh the project. This step is sot.r,erimescalled t\e feaibiüry stud!. Thc purpose of the research conducted during the dcfinition phase is to ensure that the projcct can, in fact, be accomplished.The early portion of this reserrch will result in a coarse or macro level block diagram; alr example is shown in Figure 5-1. This block diagram will show, in somcwhat general terms, the circuits that will makc up the frnrl project. If the re searchshows that certain portions ofthe project are very sophisticated or are a new use of an existing technology, some ofthe circuitry can be simulated or built arld tested as a'proof of concept" that the circuitry calr be used in this project. Thc goal of the researchis for the designer to be reasonablycertain that the project wil work. Figure 5-l Bdsic BlockDidgrom At the end ofthe defrnition phase,a complete set ofspecifications for the project is developed. These include electrical specifications as well operating specifrcations that detail the operation and human interface to the project. Although spending time on the human lactors aspectofthe project is usually apinst the engineer'sinstincts and inclinations, it ts important to ensure that the finished project not only worls büt ,lso fu161lsits purpose m tcrms ofoperxtion. In many s1.stens,a lot nore effort gocs into creatrng an oPerations spec ifrcation thxn goes into creating an elecüical or functional specification. In a cornmercial envnonment, a Project Proposal is written to summarize the definitron phaseofthe proj ect. In addition to summarizing thc researchard feasibility testing and pro viding a witten list of the project specifications, the proposrl wifl indude an anticipated budget for the project and a schedulc for completion ofthe project. The purpose ofthis proposal is to give the customer (or uppcr management) confidence that investing money in this project will result in a successtuloutcome. Figure 5-2 presentsone possible oudine for a project proposä]. Praje.tDere/a?ne"t ProjectTide A. Description of project. This section w l An$ describe the project, its overall function, the reason or rationale to complete the project, and an indication ofthe beneflts expected to arise frorn completion ofthe project. The purpose ofthis section is for the reader to understand what the project is and why it is important. B. SummaryofResearch. The project research completed during this phase of the prcject is summarized, including researchdone on the market anayor competing prod ucts, on similar or related projects or products, aswell as the results of any proof-of-concept testing completed. The purpose of this section is to show that the project has been thorouglily researchedto assurethat the relationship ofthis project to other, existing, projects is clexr. C. Block Diagram. The overall, macro-level, block diagram is presented in this section. Following the block diagram is a discussion of thelnttian of eachblock a: it relatesto theProjut\ aa'eru fu,trraz. The purpose of this section is to give the rcader confrdence that the pmject can be completed surcessfirlly. D. Project Budget. A detailed budget is presented herc to show all the e4ected erpenditures, including labor and materials, associatedwith this pmject. E. Project Schedule. The project schedule shows the milestones for starting and completing each btod., for starting and completing each phase of the development process,for review or reponing points in the pmject, and for the 6nal completion and presentation of the pmject The purpose ofthis section is to show, realistically, the tirne it will tak€ to complete the project and to give the reader conidence that the project has been thorcughly planned out. E Appendix. The appendix includes the bibliography developed during research and any other infomation that is too lärge to be included in rhe teyt. Fi8ure 5-2 PrcPosdl Outline 259 260 The defrnition phaseis a relatively short but very critical step that consumesapproximately 10 to 15 percent of the total project time. This step is crucial in guaranteeing that the completed project will do what it is designed to do. 5 . 4 . ? D E S I G NP H A S E The major goal of the design phase of the project is to flll in the macro blocks developed during the definition phasewith actual circuitrv and to plan out, in flowchart form, thc project software- Becausethe hardware and softwre of the project are intimately related, the hardware design and the software plan must be accomplished corcurently When thoroughly done, this step rvitl consume 40 to 50 percent of the total project time Unfortunatelt the following two characteristics seem to reflect the approach of manl' engineers to the definition phaseof the project: th€ suc. DesiSning the projectis the stePthar,morethananyother steP'determines etn.ient' proiect, develoPment-for function and ef{icient both in termsof cessof the read"on time andunderbudgeC' . Designing and€venhatedby disliked, the projectis the st€pthat 's mosrneSlected, to doirg härdware or writing vasrly prcfer hookrng uP engineers,who ProSrams reseärchand DaDeruodc Designing the project involves going from the somewhat hazy notion of how the project might wor! which rvas developed during the defrrition phase of the project, all the wny to the completed schematicsand sofnvare florvcharts. The design phase of the proiect doesnot involve any protoq?ing of hardware or writing of any soft-are. The processof designing thc project is sholvn sepa;atelyfor hardware arrd software belorvHardwaredeveloomentsteps: t. Stan with the basicblock diagramdevelopedduring the dennition Phase.Thisblock diagramwill very likelyhaveblocksthat encomPassmore than one function.For example, if you were developinga dwice to record automobilePärameterssu€has sPeedof consumption,andthe denectionofth€ sPrings,youwould Probath€ vehicle,gasoline bly haveone mäcro block that says"sensors with a d'rect lin€ to the microcontroll€n Or you might havea sinSleblock for eachsensorw'th a line to the microcontrollei as shown in FiSure5-l The objecAnd you might häveone more block for a disPlay, tive ofthis step is to providea startingpoint in the form of blocksthat you knowwill providethe desiredresultsif you can fillin the blockswith äPProPrbtecircuitry 2. Thoroughlyresearchboti relevantcomponentr and circuitsto determin€what sort of circuitry and componentscould be usedto fill ach blockAs you determinewhat com' ponentsand circuitsyou are goingto use,youwill naturallybe breakinguP th€ Project blocksinto smallerblock.The obiectjveis to break eachblock into the smallestPi€ces that you planto indierd,olttest.Whencomptete,eachblock shouldbe labeledwith its signaldefinitionsare then usedto input and output voltagel€v€lsand/or signals.These developtest5for the individualblock. Figure5 3 showsonly the sPeedsensor (oneblocks. third of the sensorblock in Figure5-l) brok€n up into reäsonable,testable, Prajüt D.aek?ne"l Nony sine r%r'ß anging Fon 3 \'pp b 4j Vpp *tos fi.o 'cn . i nLk,l b'pred. 0 I l<hz=o100MPH. Figure s-3 Exponded Sensor Block 3. Using your r€seärch as a basis,develop a tentative circuit schematic for each of the block that containelectrcric circukry.Use a circuit simulatorsuchas SDiceor ElectrcnicWorkbench@ ro simulaterhe operadonoI your circuir./. Modiryyour circuitr/ as requireduntilthe simulatorsaysit work correctly to fulfillthe purpose of th€ bloclc 4. Use the individualblock €ircuitsto create an ov€rall sch€maticfor the Droiect.Use "cut änd päste"te€hniquesor, alternativ€ly, combinethe circuit schematicsso that errors are not lntroduced by redrawingth€ block circuits into a singleschematic. Software development steps: | . List the tasks to be comDleted by the software. 2. Prioritizethe task and determine which are critical and will needto be handledon an interrupt basisand which are l€sscritical.Usint our example,timingthe speedpulses would probablybe consideredcritical and,hence,a cändidatefor an interrupt,whereas updatingthe displaywould probablyb€ consider€da low-priority task that could be completedwheneverthe processoris not doinSmore criticäl tasks3. Create a software flowchart or outline for qch interrupt function. 4. Cr€ate a softwäreflowchart or outline of the progräm code to completethe project! entir€ täsk. When the project has been thorougl y designed, you will have a detailed block diagram (showing all blocla and signals), a complete set of schcmatics (as yet untried in hardware), and a set of software flowcharts or outlines. 5.4.3 TEST DEFINITION PHASE The test definition phase of the project has the goal ofensuring that the project meets r11of its specifications and goals (determined in thc project definition phase) through the deveF opment ofa test specifcation for the pmject. The test sp€ci6cation is divided into two parts: intermediate tests and fnal. or svstem. testsThe test specification for intermediate tests is a list offünctional tests to be performed on each block or group of blocks in the project- The tests ,re designed to ensure that the 261 262 sectionofthe projectbeing testedwill fulfrll its function. For instance,if,vou are testing a Butterworth lilter, you will need to speciS the fiequency range, the number ofdata points, and erpected results for the block test. The final test specification is a document that includes all of the test procedures which will be used to verif' that the project prototype rneets all ofits intended specifications. In the commercial environment, the 6nal test specification would very likely need to be ap provedbythc customer,and the resultsofthe 6nal testiq presentedto the customerupon completion. 5.4.4 BUILDANDTESTTHE PROTOTYPEHARDWARE PHASE Building and testing the hardware should be relatively setf-explanatory In this step, you should construct and thoroughly test the hrrdr*äe for the protogpe project. Use the actual input and output devicesfor testing wherever possible.If using the real hardware is imprac tical (such as the speedsensoron a \ehicle), then use electronictest equipmentand other circuitry as necessaryso that you will be able to supply simulated inputs fiom each of the sensorsto test the blocks or sections ofthe project as specified in intermediate test specifi cations. Keep any signal simulators developed handy so they can be used during system integration and softrvare development. At the completion of this step,you should be absolutelysurethat the con€ct input signalsare being applied to the microconüoller from each sensor and that the correct output signals from the microcontroller will drive the ouput circuitry in dre expectedmanner.The purposc of tlis step is to remove the quardary that occun when some portion of the program docs not seem to be interacting with the hardware conecdy Usualty this leads to unccrtainqr on the developert part as to whether the problem lies in the circuitry or in the software, but in this case,becausethe circuity has a[ been tested,the developerwill be relatively surethnt thc problem lies with the software. In some cases,1'ouwill frnd it is €asierto t€st those portions ofthe hardware that are driven by the microcontroller through the use ofthe microcontroller itsell Ifyou elect to do thi<, combine the effort with the ne:.t step, the S).stemIntegration and Software Development Phase (also known as Write and Test Sofozre), as you develop the tunctions to drive the output devices. In this way, you will be spending,vour time developing uscful tunctions rather than simply developing test code that must be discarded later. 5.4.5 SYSTEMINTEGRATIONAND SOFTWAREDEYELOPMENTPHASE This step is the software corollaq'to the hardware step above.Writing and testing the soft 'ware means to develop and ind;v;.l aI! test e^ch ofthe functions that you flowclurted or outlined when you designedthe project. Use a sirnple na;no fincnon to exerciseeach ofthc individual input device functions arrd output device functions so that, aswith the hardware steps above,you are absolutely sure that eacJrofthe individual input and output functions works coffecdy. Again, this step is to remove the uncertainty that rvill occur later when things do not lvork as you expect tlem to. Prajert Dcacta?ne l When the individual tunctions are working corecdy, writc thc ovcrall software in I stepwise fashion-adding one additional fünction to the code and debugging it beforc adding more-until the entire project is functioning correcdy using the ieal or simulated inputs. It is often usefirl to develop the code to run the output devices6rst so that yoLLcan use ourput devicessuch as displal's to show results when testing the input devices.Ir is also useful to use the serial teminal program in CodeVisionA\tR to display intermediate results as a means of debugging and testing your softwareThe goal of this step in the process;s to have a fully workng project using the real or simulated inputs ard outputs. 5.4.6 SYSTEMTEST PHASE The system test is the activity that actually puts the project into use.During the sl,stemtest phase,the project should be tested in accordancewith the final test specification developed earlierto ensurcthat all ofthe specifications defned in the defnition phaseofthe process For a commercial project, the system test phase will also include a demonstration for the customer, and it wiJl often include transfer of the inkneüaal ?roperrJ OP) rclating to thc project. The lP includes complete documentation and rccords relating to rhe project, and it may be the propertyofthe customer,dependingon contractand businessstipulations. 5.4.7 CELEBRATIONPHASE Successfulcompletion of a project is always a good rcason to cclebrate. It is beyond the scopeof this text to suggestthe ways,means,and extentofyour cclcbration.Just cnjoy it. 5.5 PROIECT DEVELOPMENT PROCESS SUMMARY The projectdevelopmentprocessis summaizedin Figure5 4. This 6gurcshowscachofthc steps)the e)eectedintermediateresults,and the final resultsor dclivcrablesfrom cachstcp. 5.6 EXAMPLE PROJECT:A WEATHER MONITOR 5 , 6 . I C O N C E P TP H A S E As an example, supposewe are enginccrs at the Wind Vanes R Us Company, which has recently begun looking for *ays to erpand its product offerings. At lunch one day with our fellow \WRU employees, someone comments on how they are underdressed for the currcnt wcather. This leads to a conr.ersationon the dubious accuracv ofthe locrl weathcr forccaster and horv it would be nice to watch the weather indicators ourselvesto know how Further discussion leads to some speculation on rvhat weather paramctcrs rvould bc useful to measure,and eventually a napkin is used (projects often start with a cocktail napkin and a pen) to start sketching out the attr;butes of such a slstcm. 764 Expect?tio,rJRdltJ Conplete projed s?ecifications Scnedulc B"dg"t Final, det iled blo& diagram Design Phase Cinit simülition aulu FlNclans for eachintempt tunction Flowcldt for the pmjed Testspedfic.tions for eachblock or section Final test speonc ions Build andtst the IDdividual block tcst resdß Individuar function test res ts A onpleted, nüy function l prcject Prcjectdmentatior Figure 5-4 ProiectDevebpnentPrc.essSum'l,,ory In the design ofthe weather monitor, ot r list might look like this: . Easyinstallation . Collectasmanytypesofw€aüer dataaspossible ' Simpleconstruction Expanding on oul list ofattributes, we speculatethat the weather monitor would consist of tlvo units, an indoor unit and an outdoor unit. The outdoor unit should collect asfew para met€rs as possiblein order to make it as simple as possible.Temperature, wind, rainfall, and humidity must be collected outside, since that's where the actron is. But barometric pressure is basically the same inside or ouq so why not measureit indoorsl Indoor tempemtüe and relative humidity musq of coürse, be measurcd indoors. There s also a factor of time when looking at weather. We might want to know when something happened, perhaps log some data, such as when there was an occurrence ofhigh winds or very low temperatures.A real-time dock should be incorporated into the indoor unit. 5.6.2 DEFINITION PHASE We can 6ll in our list ofwants ftom the concept phasewith more details, embellishing or deining each concept that has been put on paper Notice that no anempt has been made yet P,aJ..t D.retoPfleht to determine whät is feasible or possible at this point. Remember that tle goal ofthis phase of the project is to develop a very basic block diagram of the system and a complete set of specifications for the project. We start by expanding orx list ofconcepts: l. Easyinstallation a. Wireless-9ooMHaone-wäYlink b. No exteroal power requiredon the outside uniqsolar/battervPow€r€d c. Outside unit battery to lastthrough ä rainyweek d. Simplesetup(wewouldliketo be ableto iustPuta Pon uPin the yard) e. LCD on insideunit GrJPhicalwould be cool, if not too exPensive) I Buttonsfor the userto vi€w difierent Piämeters and set the time on ti€ inside I Off-the-sher power supplyIor the insideunit,with battery backuPfor the clock 2. Collect as manytypes of weather dataäs Possible andoutside a. Temperature,inside b. Wind speed for the w€ather c. wind chillwouldbe Sood it helPsin dr€ssing d. Wind direction €. RainEauge t Baronetric pressure g. Relativehumidityinsideandoutside (would be neat,if not too €xP€nsive) h. Dew point (ShouldI Parkry convenibleinside?) port on the insideunitto monitorw€atherwith a PC? i. RS-212 3. Low cost a. Eväluatethe costsof eachgPe of measur€mert (asf€w Partsas Possible) b. Keepthe overall consüuction inexPensiYe 4. Simpleconstruction a. Partsshouldbe availablefrom €ary-to-buysources b. simplefeedbacksyst€ms,noti;ng too exotic c. Wind and rain Sautesshouldbe simPl€to construct o. off-the-shelf This eryanded list provides n better "mental picture' ofthe envelope that we are trying to *o.k *ithi". A" *" e*panded the list, the wishes formed- At the sametime, complexity r nd cost werc also noted, 265 266 This is the sameprocesswhether you are designing something for yourselfas a hobby or you are sitting in an Engineering/Marketing meeting discussing the development of the next product at your company, as we are doing in this case. 5.6.2.1 Electrical Specifrcation Now that we hav'ea wish lis! rae can expand the definition to build a performaoce specilication. This is where a set ofparameters is assignedto each function or feature, indicating its range ofperformance and tolerance. Performance specfications do not al*ays need to be created. They can be found, in many cases,by looking at sirnilar or competitive products that already e\ist. The preliminary functional specfications for a weather monitor might look like those in Table 5 1. Huidity -'lO" to 1,107 +/ 1"F 10 o 9096RH +/ 5% RH +/ 0.05inHg 2a 'o32 nHg Rainfall 0.00to 99.9inchs daily Rainfal monthty/yeül/ 0.00to 199.99in lles 2 to 120 mph 4- 2 nph 0 360'@1' resolution -{T to 117F -102T ht 487 Dew Point Wind Ch +/,2'F +/ 2'F 24 tL, 1 S* retutior Date (C,lendd) Tabfe S-f MM DD YTTY N/A Weot?erlv€osütütentPtelininoryS|e.ifßotions 5.6.2.2 Operational Specif cation Becausethere is a human-to-product interface involved in our weather station, an operations specifcation should also be developedA good way to begin is to make some sketchesofwhat the display might indicate and write a list or even an Operatort Manual about how the button selectionsaff€ct the operätion of the device. Txking these steps early will gready reduce the software developm€nt time in many cases,simply becauseofthe psychological effects ofhaving a list. As items on the list are completed, check tiem off The operational specfications for our weather monitor might look like this: Outdoor unit Operational Specifcation: | . Keepunitr basic,ADC änd timer counts is okay 2. l'4€asuretemDemture. , "::::::?'\'11" 3. l4easure humidiry. 4. l"leasure windsp€€d. 5. Measure wind direction. 6. Measurerainhll. 7. Measurebaftery/solar-panel voltage. 8. Transmir the informationto indoorunit,approximately onceper second. 9. Enablethe radiofrequency(RF)modulepoweronly duringtransmissions to sav€ ener$/. Indoor unit Operational Specifcation: L Measure temperature. 2. l4easure humidity. 3. Measure barometricpressure4. Measur€battery/wäll-powervoltage 5. Ke€pa reäl-timeclock 6. Gather packetsof informationfrom outdoor uniqasthey come in. 7. Using4X20LCq representasmuchinformation aspossibleon a sinSlescreen,indi. catingindooror outdoorandrelativeuni6.asmuchas possible. 8. A "Units"buttonwill allowthe userto changedisplayunits,"F to "C. mphto kph,and 9. A "Select'buttonwill allowthe userto selectraintallreadings from inches-per-hour, to inches-per-day,to inches-per-month,to inches-per-year. | 0. A "S€C'buftonwill allowthe userro s€t the time änddare. I L Enabl€LCD backliSht onlywhenwallpoweris available. | 2. Includea "low battery"indicationLED: a. The LEDflashes whenindoorunirbatteryis low. b. The LEDis on solidwhenoutdoorunit batreryis low. 13. lncludeRFcommunications activityLEDto indicateoutdoorunittransmissions. 5.6.2.3 BasicBlock Diagrams Using the data that we have put together so faFthe wish list, the expandeddelinition, and preliminary performance and operational specfications-we can dmw some basic block diagrams of the systen. The diagrams shown in Figures 5-5 and 5 6 show the basis for the hardware architecture. The power supply, what parameters are measured where, and the method ofoutpufting the processeddata, whether it is by RF or LCD. 264 Rtsc ÄN2 T1 Fieure 5-S Blo<kDiocnn,outdoor Unn The block diagrams show a detail that is determined in the feasibility study of the defnition phase.On the blo& diagram, the inputs to the microcontrollerure nrmed by the hardware function of the input. The following section describes how each ofthe measurements ß taken and what kind ofinput to the microcontroller is required. It is important to do this in this phase of the project because tie number of special inputs, such as amlog input or timer/counter input, is limited on the microcontroller. Using the block diagram as a guide, we can choose an appropiate microcontroller with sufficient VO and special features.As we go on through the design process,we can then check our chosen microcontroller against the project needs to ensue that we have made a good choice with the micro. The AIMegal6 was chosen for the prototyp€ development. The Mega16 is pin-for-prn compatible with the smaller-memory model ATMega8535 as*.ell aswith the larger-memory P/ajett RISC Dett/afne l "'&"iT.- ooo FiSur€ 5-5 Unit BlockD,ogrsm,lndoor model ATMcga32. This allorvs some freedom during the design phase. The option of increasingthe menoq modcl may be needed,since we do not knorv exactly how much codc spaceis requned in either unit. At thc cnd ofthe project, alrd after the features have ceased to creep, if the code rvould fit into a potcntially less axpensivecomponent with a smaller memory size,that choice is availablc aswell. Thc othcr, pcrhapsmore obviouspoints ofselection are the availabilityof .{DCs (analogto dignal convcrtcrs), a USARI and an osciJlator&iver for the 32 kHz crystal for the rcal time clock. CONSIDERATIONSFORTHE DESIGN 5.6.3 MEASUREITlENT ' checkofthc system. Thc 6na1stcp in the definition phaseis a feasibilie srudyor'tmin Now that wc have specifiedrvhat rve zazr the rystem to do, can we neet thosc cxpectations, or do they need to be revisedbasedon ph-vsicalor electricallimitations?This section dcscribesthe stepstaken to ensurethat our project n feasiblebeforc \{c move on to the designphasc. 270 It is hard, however,to completely separatethis final step ofthe definition phasefrom thc design phase.In many cases,it is necessaryto develop very specific details about the design to ensurcwe can measurcto our specifcations. So this section crossesinto the design phesc m many areasaswe explore the physical and electrical requirements ofmeasuring the weather Examining the basic block diagrams, you may note that there are common elements.Temperature and humidity are required both indoors and outdoors, but they are fundamentally th€ samemeäsurement becauseanalog voltages representthem both. Wind speed,rvind di rection, and rainfall are outdoor only items. Arrd becausebarometric pressure is basically the sane indoors as it is outdoors, why not measue it in the best possible weather conditions, indoors? Each parameter in a system may require a different method for determining its value. In some cases,the parameter can be measuredin severalways, and it becomesmore of a matter ofselecting what is appropriate basedon performance, cost, or both. The design consid erations for each parameter being measuredare discussedbelow. Once the method of measuement is selected,it is checked for total ränge and resolution. When you deal with voltages and ADCs, the resolution ofthe ADC is rhe pacing factor. When pulses are brought into a counter, thc size oftie counter and the mte at which the counts are checked determine the range and resolution of the readings. In this weather monitor project, temperature, humidity, battery voltage, and barometric pressureare all voltages that arc processedby the ADCs. These are calculated out to verify that everything is within range and that the specifications can be met as the scctions are designed.The wind speedand rainfall are not quite as staightforward. 5.6.3.1 Temperature Temperature can be detected inexpensively and simply using a PTC (2aritixe tem?entare eo efie;ent) or N IC (negatioeten?e,ature eoefre;ent)rcsistive device, or thermistor These devices come in a wide range ofvalues, and with proper selection considemtions, no specirl amplification or conditioning might be necessary. There are many other temperatüe sensoß available, including bi-metal thermocouples, temperature compensation diodes, and rastia:oatenperunre devnu (RTD). There are also integrated circuits, such as the National Semimnductor LM35, that are calibräted, stable 'C. For example, the measuring devices which deliver a speciEc amount of voltage per is either more costly or requires addiLM35 outputs 10 mV/'C. Each ofthese, however, tional circuitry that makes its use more cosdy. A glass encapsulatedNTC thermistorwas chosenfor oul design to do the temperature sens ing. Figure 5 7 illustrates the resistanceveßrustemperature of a gpical NTC thermistor. Since thermistors move in ralue as a percentageofresistance per degree C, using a resistor divider allows for a reasonably linear measurement of temperature. The dividert voltage Proj..t D.oelofnef,t 20000 15000 10000 5000 0 Figur€ 5-7 NTCRes,innoeyersuslempero&re outputrang€canalsobetailoredto matchthe rangeofthc ADC, providingthe bestpossible resolutionfor desiredrangeofmeasurementThis iswherethe NTC devicehasan a&rrtagc overan integratedc crrit like the LI\ß5. It would take additionalcircuiüy,plus the added cost of the LM35, to g€t a rcsult comparableto the NTC solution.The output rcsult of the NTC/Resistor divider may not be perGctlylinear,but we can usesoftwaresawy and look-up-tablesto fx anlthing thet is not deemedacceptable. The Mega16processor, aswith the entircAVR family,prefen a circuit with a fairly low out (about 5K ohmsor less)for input into the ADC. We selecteda 4.7K resßflrt impedance tor to form the dividerwith a 2K thermistor(approxinateresistance25'C or 77F). The selectedthermistorchanges3.83 percentin valuefor every1"C oftcmperaturechange(from the thermistor specification).This providesa iange ofvoltage to the ADC ftom approxrmately 0.84 V at -.40T to 4.5 V at 1,tO"F.The thermistor was placedin the top of the divider becauseof its negativeimpedancechangewith temperature.This allo*s the ADC readingsto increasewith temperature.Figure 5-8 illustratesthe relationshipofthe output voltageat the resistordivider and the temperatueofthe thermistordevice. The ADC resolutionis 10bits (or 1024counts),sothat meansthat each"F is approximately 4.16 countson the ADC. We arriveat this nurnberby 4.5v-O.84Vranqe . 1024 counts 5 v (fu1t scale) = ?49.56 counEs for the ranqe 271 272 Voltoee f6n 1.7 K DM.r.. 5 3.5 3 2.5 2 1_5 1 0.5 0 Figure 5-a Nrc/ResinotDividerOuryüVeßusTem.percute where the range is 40"F to 140"F. This means we have a resolution of approximately 0.240"F for each count ofthe ADC. The calculation for this is 140rF - {-40.E) 749.56 This resolutioo shows that the measurement accuracy is sufficient to m€et the project temPerature accuracyspecfication of +/- 1"E 5.6.3.2 Barornetric Pressure Pressure can be detected using oflthe shelf transducers.These devices come in a wide range ofralues, and with proper sdection considerations, no special amplificatron or conditioning might be necessary.Bärometric pressure is measured in units of incbesof mercury (inHg). In fact, a total range offour inches ofmercury is typical, as suggestedby researchon similar wenther stations. Therefore, a fairly sensitive detection is required. Pressure transducers usually come in th-reeforms: gauge, differential, and absolute. The gauge (PSIG) and differential (PSID) transducers,in both cases,measure pressuredif{er entialy (the difference between two pressures).A gauge pressure tnnsducer measures against ambient air--pecifrcally designed to ensure thrt rro barometric pressureis figured into the reading. A differentirl tansducer measuresagainst a referencepressure,so that the barometric pressurethat is awilable ät both inputs is cancelled out. An absolute transducer measuresdifferentially against a vacuum (0 PSIA), so the Fessure being read includes the elfects ofbarometic pressure,maling it appropriate for this project. The SenSlrn ASCX3oAN ts a0 to30PSIA (?ounds?et sqaare;nrh, absal te) ptessnreilansducer In the weather monitor, we simply open the sensorto the outside air. This meansthat Pt'je* Dexe/a?he,t the only pressuJedetected is b?rometric. The range ofbarcmetic pressureis very nr-üow.It is generally measuredas 28 to 32 inches of mercury.This translates into a pressurerange of 13.75 to 15.72 PSIA. According to its specifcation, the ASCX30AN has a sensitiviq' of 0.15 V,4SI. That means the actual output voltage ftom the 13.75 to 15.72 PSIA range would be 2.06 to 2.36 VDC. This is not much signal! Consequendy, it is necessaryto provide some amplification and DC oiTset to the transducer signal before it is applied to the microcontroller's ADC. Providing an amplifier with a gain of 16 boosts the woltage range from the sensor to a useirl (2.16 V 2.06 V) . 16 = (0,3 v: 16 ) = 4-8 v A range of 4.8 V usesmost of the 5 V input range on the ADC, mrximizing the abiliq' to accuratelymeasue the signal. For this to wor\ however,the 2.36 V DC offs€t must be sub tracted lrom the sensor\rcltage before it is applied to the ADC. A differential amplifier is used to provide a gain of about 16 to the signal as well as an offset of-2.06 V This allows the ADC to acquire a signal that ranges from 0.0 to 4.8 V DC for the 28 to 32 inches of mercury- The total range ofADC counts for the mensurcment rangeis 4,8 v 0,0 v iange . 1024 counLs = 943.04 counts for the ranoe 5 v (fu11 scale) where the range is 28.00 to 32,00 incles ofmercury. This means we have a rcsolution of approximately (32 inHg - 28 inHq) = 0.0041 inHs 983.04 0.0041 inches of mercuy for each count of thc ADC, which more than meets the desired accuracyspecification of +/- 0.05 inHg. 5.6.3.3 Hürnidity Hurnidity can be detected using off-the-shelftransducers as well. These devices are ther mally compensatedfor accurary and are fa y expensive.Using a humidity-sensing capxci tor could create a less expensivesolution, but a large effort would be spent on compensating and processing the device input to form an accuratehumidity measurement. In this weather monitor, humiditv is measured by an off-the-shelf temperatrjre compensated humidistat. It was a decision based on easeofimplementation a1one.This is not the least e{pensive solution, but it is cenainly simple to integrate and very accurate.The device used in this design is a Honelvell (Micro Switch) HIH-3602-L. The device outplrts a processedDC voltage from 0.8 to 4.0 V for 0 to 100% humidity. The output ofthis device may be conncctcd directly to the ADC input of the Mega16 processor The total range of 273 274 output from the ADC for the humidity rangeis 4.0 V 0.8 v range ' 5 V (futl 1024 counls 65r. l6 .o .a s or rh- tanqe scale) Using this number, we determine the resolution for humidiry measr:rementas follows: 100* - 0g _ = 0.1529 655.36 An accuracyofmeasurement of0.156% is way more tlun adequateto measurcthe RH +/- 57o as speciEedin the electrical specifications. 5.6.3.4 Wind Speed Wind speed is gpically measuredusing a set ofrotating cups or a fan blade arrangement called an anemometer.Basically, as the wind blows, the anemometer turns at a speedthar is directly related to the wind speed.A device that m€aslres the rate at which something is turning is cal1eda tachometer. Several possible tachometer types are used for wind speed One often used form of a tachometer is like a small electric motor or generator. As it turns, it generatesa DC voltage that is related to the mte at which it is spinning. In this case,the resulting DC voltage could be measuredusing the microcontrollert ADC and the wind speedinterpreted from the DC voltage. Another version oftachometer ls t\e digital tachonrrs,: A digital tachometei g?icaly generatesa pulse train, associatedwith the rate ofspin, which car be measuredas a lrequency and converted to 'ez'rlrt;ans ?er ni te (rpm). A digital tachometer is, in most cases,a less erpensive alternatrve to an analog tachometer. It can be easily constructed from a slotted disk and a photo-interupter or opto-coupler.It can also be an off-the-shelf solution in the form of an optical encoder- Since there are no magnets and much less inertia due to the weight of the armature, t}rc digital tachometer also offers an advantage over the analog tachometer becauseit usually imposesless drag or the system. For our weather monitor, an off the shelf anemometer was selected.This selection was made for the sakeofmechanics alone (seeFigure 5 9). Ifyou are a panicularly handy individual, 1ou might be able to construct an assemblythat would provide similar results at a gready reduced cost. This particular unit uses a magnetic reed-switch for encoding the speed.Basically, a smal1 metallic switch is mounted in tlle base,and a magnet is mounted on the anemometer As the anemometer turns, the magnet makes and breals the switch dosure. This is a simPle solution mechanically, but it lacks some electrical quality. Since the switching is not electronic in nature, there is a high potential for switch "bounce." Switch bounce isjust that; the contacts literally bounce Jike a rubber ball as they are slapped together, creating sevenl transltions as the switch is made. If this signal is brought direcdy into the timer input of the Püje.t D.u/a?n.nt ffi wSo-eeDualWindSpeed/Directlon Sensor into The l\Ioclel0344 Wind Sensorcombineswind speecland directionmeasurements a single remotesensing unit. The 0344 WindSensorinslallsn minutesand wil provde longterr.,continuous montorlngjn hostileenvi accurate, . Windspaedard d re.lio,lir a sinqe sersor. . Durablealuminunr andslainless steelconsiruciion. . Lowstarlingthreshold. . Stalnless slee bearings. Operation: The 034Ais designedlo operalewilh n atemperature range of -30'C lo +70'Cand with wind speeds up to 155mph. Wind speedjs measuredusinga sealed reedswiichlhai providesa series ol pulsesdr d rarFproponroralro wir d speed A Jninrr c.p: a e usedfordurability.Wind directions measureduslngan alumlnurn vane d recty coupledlo a preclsionpote.lior'reterVarialionsin wind d reciionproducea correspondingchangeof voliage,which lends llselfto bothdigllaland analog measuremenisysiems. Construction: andhigh-gloss whitepowdercoaling Highqualtyaluminum andsläinlesssteelcomponents. Cablelengihmayexiendhundreds ot feetwilhoul ensurelong ifewithrnnimalmai/rlenanceaffeclinomeasurer.ent Derlormance. WSD-PBSpecitications Fange:0 155mph(0$9 nts) SiartingThreshold:0.9mph{0.4nts) Accuracy<22.7mph:0 25 mphi0.1m/s) AccL,racy > 22.7mph:11.i%ot true Mechanical:0360 StartingThreshold:0.9mph(04 m/s) OämpingFatio:0.2sslandad(0.4ro 0.6oplional) outputsi9näl wind Speed:Pulsedcontactclosüre oulpul(0-10kohms) WindDirectioniPolenliometef Range: 30"c ro +70' c Temperature SensorWeight1 lb 12.5o2(0.81kg) Rqrnt ritr; Figure 5-9 WSD-PB DudJWindSpeed/Directon Sensor rt t trst Tin ükg Stft^ ht. 275 276 microprocessorlvithout any d€ bounce circuitry or frltering appfied, eroneous data will result, becausethe timer receivesthree to tcn times the number ofuaasitions the switch actually made based on the mph of wind. ConsequentlS some de bounce circuitrl will be needed to provide accuratewind speedmeasurement,as shovrn in Figurc 5 11, the outdoor unit schematic. The specifrcation for this device sho*s that it will measurewind speedas slow as 0.9 mph and is accurateto 1.1%ofmre wind speed.At the highest speedwe specified(120 mph), the accuracy would be 1.1% of 120, or 7.32 mph- This exceedsour speciied accuracy of +/-2 mph. The wind speedinput in this project is a pulse train. Our plan is to count the pulseson one of the timer inputs änd get a total every second,in order to compute wind speed.To check what we arc capableof measu;ng, we need to know how fast the fan or cups of the anemometer spin with respectto a certain wind speed.For now, we carrassumethat the anemometertums 0.15 rc'\'olutions for every 1 inch oflineal air that passeddrough it. That would mean that 1 foot per secondwoold translate into 1-8 revolutioß per second,which is 108 rpm. At one mile per hour, the wind would be traveling at 1,,f6 feet per second.This would turn the anemometer at 158 rpm. At 100 miles per hour, the anemometerwould spin at 15,768 rpm. If we place an encoder on the system that delivers four pulses for each revolution of the anemometer,a one-mile-per-hour wind would yield 10.5 pulsesper second (PPS or Hertz). At 100 miles per hour, a pulse train of 10512 PPS would be generated.Ifthis signal were sampled at one-second intervals, using an 8-bit counter, the naximum wind speed that could be measuJedwould be one that generates255 PPS. We can 6nd the ma-rimum wind speedby working this backward: 255 pulses pe. seconil = 63.?5 rewotutions per second Ifthe anemometer turns 0.15 revolutions per one inch ofair motron, then the air speedrcquired to turn the anemometer would be 63.?5 revolurioDs per seconal 0.006707 niles per second 5280 feet per nite 0. 006707 niles per second . 3600 seconds per hour = 24.14 npl] Our inltial specification is to measure up to 120 mph, which is an ertremely strong wind! What this crosscheck shoüs us is that we will need to sample the counter 5 trmes per second, or every 200 ns, to prevent the counter from rolling over during our measurement. Praj.rt Detetafn.hl It also shows that the anemometer can have ouite a variation in the rclationshio between wind .peed and -pm and we wiil srill bc saleFom a design,specr. Ifthe unit gets all put together and we find out that counts generated at 120 mph will not fit within the counter in 200 ms samples,we willjust read the counter more often, maybe every150 ms instead.On the other hand, ifwe fnd that the relationshipis much less,we can read the counter less often, reducing the sy'stemoverhead. Another method for improving the measuemeflt capacity h to simply get a bigger counter Timer 1 is a 16-bit counterand can hold a välue256 timcs lareei This meansthat we can effe,r:vely'an-pleaLone-6fticrhthe rate.or onceeueryten I'rhe ,rnp lng 11q ;' "ec-nd.l even once per second,the collected number in Timer 1 would effectively be live times larger than what could be measuredwithin the 8-bn counrcr. 5.6.3.5 Wind Direction Wind direction is usually determined by tie useofa "wind vane" or 'weather vane," our spe cislty at Wind Vancs R Us. A rveather vane is generally a 6nned shaft, something like an arrow, tlat is constructed to pivot in a horizontal fashion. The vane is ftee to turn. The 6ns create drag and are effectively pu11edby tie wind such that the point of the rane indicatcs the directionoforigin of the wind. Determining thc wind dnection is a matter ofencodirrg this positionsuchthat the compassdirection ftom 0" to 360",where0"is north,90" is east, and so on can be read electronically. This can be accomplishcd using an optical encoder, a continuous tum potentiometer, or a simple mechanical switch encoder. Optical and switch encoding is generally considered a relative measurement.This means that a 'home" or zero ooint is established. and the e.coder indicatesthe distancefrom that establishedhome posirion.There rre absolureversionsofencoders such asa Gray Scaleencoder; these encodersoffer a different code for each position within a single rctation of the encoder.Thc disadvantageto this g?e of encoding is limited resolution. A four-charrnel Gray Scaleencoder offers a 4-bit rvord ofinformation regarding the position within a 360" rotation. This lirnits the discernible number of posi tions to 16, or 22.5" ofrotation. Using a continuous turn ?orenrioneter otreß l;ßtrcr resolution. A potentiometer, also known as a rheostat or vaiable resistor,offers an absoluteposition effcctir.ely at an infnite resolution. The limiting factor for encoding the position then becomesrhe resolution of the ADC or other measuring device used to read the resistancevalue. Potentiometers are qpically not continuous-tum devicesbut are more commonly single tum or 10-tum dei.ices.Somesearch ing may be required to locate one if1,ou areplanning to build your own rvind-direction sensor. The Forest Teclnology Slsterns, Inc. WSD-PB Dual \{ind Speed,Direction Sensor, as shown in Figure 5-9, uses a 10K ohm continuous-turn potentiomcter. Note that in the specfications the measurement range is 360" but the usablerange is 356'. This is becauseof 'dead a sma11 spot" where a single tum pot would normally stop. This 'dead spot" could be used to establish a North or South referencewher the weather monitor is set up. 274 Thc ouput ofthis device can be tied dnecdy to the ADC input ofthe Mega16 processor. Thc ADC is 10 bits (or 1024 counts), and the voltage from the sensorwill go rail to rail, or 0 5 V DC. So that rneansthat each 1" of position is approximately2.876 countson the ADC. We arive at this number by 1024 counts = 2-876 counLs per deqree 3560 where the positional range is 0 to 356". This means we harr a rcsolution of approximately 0.347' for eachcount ofthe ADC. This result is far bener than our soecificd accuracvof+/- 7". 5.6.3.6 Rainfall Rainfall is measuredin cubic inches. A gpical rain gauge consists ofa tunnel and a gradu'bne ated cylinder The defnition of inch" of rabfall according to Rcf 031.024 of the Anerian Farn and HameAlnanat is as follows: An acre ofground contains 43,560 square feet, therefore one inch of rainfall over one acre ofland would e+il 6,272,640 clbic inches ofwater, which is the equiva lent of 3,630 cubic feet. One cubic foot ofwater weighs about 62.4 pounds (thß vades with the dcnsity); the weight ofa uniform coating ofone inch of rain over one acreofground would be 226,512 pounds (about 113 short tons). The weight of one U.S. gallon ofpure water is about 8.345 pounds, therefore one inch of rdnfall over one acre ofgound would be 27,143 gallons ofrvatcr. The toughest part of measuring rainfall is collecting and reading a volume of water over what could be a long period oftime. There are a few common methods. One method involves a tunnel with a r.ery small spout that produces a uniform drop of water As the funnel flls up at a random rate with rainlvater, the spout produces uniform drops that can be counted over tirne. This can then be converted to a volume, over time, which can be converted to inches ofrainfall. This methodt shortcoming is that the lariation in the rate at which the rain is falling cannot be determined. It also could produce an invalid reading if the volume ofthe funnel were not sufficient to contain all the rain col lected until it could be dribbled out and accounted forAnother method is a paddle wheel anangement. A tunnel is used to fill known volume cups on a wheel. As the cups 611,the wheel tums. Revolutions ofthe wheel indicate the rxte and the amount ofrain collected, asweII as emptfing the sanples taken as the whecl turns. A reduced version ofthe paddle wheel is a seesawconfiguration. The concept is basicaly the same,e{cept there are only two cups and when a cup becomestull, it tips over to empq', bringing thc other cup into position to gain a rain sampleftom the funnel. As the secondcup 6IIs up, it then tips to cmpq-,brlnging the f rst cup back into position again.This method is probably the most common onc uscd ;n small electronic rain gauges,becauseit givesall the infbrmation neededwith a minimal amount of mcchanics.Each timc the cuos tir from one oosition to the .ignii. S.nerared. orher.a , olumeofrainsarcris accounrcd for andanclccrrical PtujeLt Deaeta?hent ffi nc-r Rain cauge The RG-TRainGaugefeaturcsa chemicallymilledtipper buckettor consistentbalance jeweledbearings and easycalibration.Thetipper bucketpivotson shock-mounted provldinga sensiliveyel ruggedlowfriction pivot to track rainlallaccurately. A precision adlustment forihe €ed swiichensuGsoneswilchclosure lor eachlip ofthe buckel.Thetipper,bearings andmagnelicreed mounting switchareheldin slurdymachined aluminum blocks.These base.Thecalibration adjuslment areseatedon a rigidcastaluminum screwsareprolecied againsilossof calibationdunnghandling. Scrcensin lhelunnelandoverthebaseplatewaterouuetssealout in a waterprool spideßandinsects, Thecable,whlchlerminales clrcularbayonetconnector,is protectedlrom rodentsby braided levelcoupled wilha precsion sla']lesssleelarnorAburh-rn adjustmenl leveling armandmounting basemakeinstalling ihe RG-TJastandeasy. The FTSRainGaugeis considered bya numberofoutside experts, lncluding lhosewitha lot otfieldexperience, to be oneof lhe bestiippingbucketraingaugesin thewo d, withan unbeatable combinaiion of quality,accuracy, andlonglastingcalibration. prccessso lhal in a specialcasting Theredesignoi lhisqualilyproductincludesinvesting we canprecision as asinglepiece,lalherthana number castlhe gaugebinlernalstructure ol separateposlsandsuppods. Theresultwillbea morcdgidgaugewiihevengreater resisiance io vibralionandincrcased repeatabilily frcmonegaugelothe nexl. RG-TSpeciflcällons Resolütion:o.o1tnpe! tip(0.254mm) Accuracy: 12%at 2 in per hour(s0 m.n) Cyllndef Dimenslon€:10-5in x I in diameter{25.7cm x 20.3cm dimeler) B . s e P l a l e D i m e n s i o D1s2:i n x 1 2 i n { 3 0 . 5 m x 3 0 . 5 c m ) cäbreLenEih:20 fl (6-1m) Weightr10lb (4.5kg) R4tiat üürttt af Fü6t Txb"at gr s!'ft]n', tn Figure 5-10 RGr RoinCduge In all of these methods, a form ofoptical or mechanical encoding is used to bring the inlor mation in for anallsis.The amount ofinformation is dependenton the sizeofthe sampies taken and the ratc at l'hich a minimum samplecan be met. Again, for the puposes ofreduccd mcchanical design, rve are using an off-the-shelfsensor from ForestTechnolog,r' Sys tems,Inc., as shown in Figure 5-10. As mentionedwith the rvind speedsensor,ifyou are mechanically inclined, a less expensivesolution could be built. As in the anemometer, this unit uses a magnetic reed switch for encoding the rainfall. Basica1l11 a sma11 metallic switch is mounted in the base,and a magnetis nountcd on the 279 280 scesaw.As a seesawtips back and fonh, the reed-switch contacts are closed and then opened again.Becausea reed-switchis a mechanicaldevice,the samerules ofswitch bounceapply as they do in the anemometer.Some additional circuitry is neededto prevent enoneous readings. Whether the measuring sl,stem is purchased or you construct it yourself, even if great care is taken in creating the funnel, sarnpJingcups, and the wheel or seesawsystem,until ]/ou put water in it you never rerlly krow what kind ofvalues the measuring system might produce. This build-and-test processin a proofofconcept stageis invaluable, paticularly when there are somewhat complicated mechanics involved and the'gotchas" ofphysics apply Things like gravity, friction, and inertia can really messup an engineer'sday. We can assumethat in this weatler monitor project we plan to use a seesawarangcment that is fed by a tunnel thät is foü incles in diameter, instead of the really nice, but pretty ex pensive,purchasedsensorthät we have selected.The concept is that aswater enters the tun nel it fills up a cup on one side ofthe seesav When the weight ofthe cup exceedsthe lever agesand frictions in the system, it will tip over.This action not only dumps the contents of the cup but also placesthe cup from the other side of the seesawunder the tunnel to collcct more rvater When this cup f,Ils, the processrepeats.The speed at which the rainfall is col lected is very slow compared to the microcontroller that will be observing the sampling. If the cups were smaller than sewing thimbles, the sampling would occur faster with higher resolution. But ifthe cups are too small, the system muld be ovenvhelmed in a heav,vran scenario. Cups the size ofcoffee mugs har"ethe opposite problem. You could go for weeks before you get one 6lled up! This would causethe samplesto come in more slowly and the resolution of the measurement to be much less. For the sake of the "sanity' checL, we assumethit the cups each hold about one cubic inch ofwater With this system built up, we could actuall]. m€asurethe sämple sizesin a sirnple and controlled fashion. One gal1on ofwater weighs 8.345 pounds. A cubic foot of water we:g\< 02.4 pounds.Therefore.a gallon ofrvater is 8.3 45 pounds pe! qal1on = 0 . 1117 cubic 62.4 pounds per cubic feet foo! 0-1337 cubic feet = 211-036 lt28 cubic inches per cubic cubic inches fooE Since the tunnel is four inches in diameter, its collecting surfacc is 12.56 squareinches. So 231.036 cubic inches = 18.39 inches of rainfall 12-56 square inches is representedby one gallon ofwater. Ifthe cups hold approximately one cubic inch ofwater then the seesawshould transition approximate.ly231 tines as the ga11onofwatcr is poured Ploject DeulaPnent into the funne1.That would meän that each transition ofthe seesawwould represent 1 8 . 39 i n c h e s o f . a i n f a l 1 = 0.0?96 lnches of .ainfatt per transition 231 tlansiEions You canseethat by simply building it up and pouring somewater through iq we coulduo coverwhat is reallygoing on- At the end of the gallon,you might comeout with more or fewercountsthan wereexpected.That is okay,aslong asyou know what they are. Our preliminaryspeciflcationcallsfor measudngup to 99.9inchesofrainfall in a day That meansapproximately4.16inchesofrainfall would occureachhour.That means,in this kind ofrxinfall, that 99.9 inches l transitior = 52.25 Eransicions pe! hour 24 hours 0.0796 inches would occur This is lessthan one transition ofthe s€esawDer minute in a downoour whne srill providing a rrsolution of0.0796 inchesof rai.nfallper rransirionlA very acciprablesrruation when compared with the +/ 4% effor specifcation for rainfall monitoring. 5.6.3.7 Dew Point Computation Dew point is a calculated number based on air temperature and humidity that te11swhen moisture will begin to coadenseon objects that are at a cooler temperature, that is, when the dew will collect on the grassin the morning or when moisture will collect inside your convertible even though the top is up. Dew point cornputation is actually quite complicated. So to reduce the effort, charts have been establishedthat provide the translations fiom temperature and humidity to dew point, as shom in Table 5-2. InTable 5-2, find the air temperature in the listing acrossthe top ofthe chart, and then find the relative hunidity (in percent) in the listing dowr the lefi side. Follow the column and row dolvn and acrossto the box where they intersei:t. This is fhe dew point. For temperature and humidity ralues between those shown, use interpolation to compute yalues between the dew points in the column or row. For example,with a temperature of 65'F and a humidity of45% RH, the dew point temperature mlue will be halfway between that for 60 and 70"F, or 31 + (47-\31 :2)) = 11 +5 = 42oF- Objects that are at a temperatue of42"F or below will collect condensedmoisture given an air temperatue of 65"F and a relative hurnidity of45% RH. In the weather station being designed, the table data will be induded in the software and used to "look up" the dew point basedon the reading for temperature and humidity 281 282 20' 30' -6 4 13 2 8 16 a0" 50' 60" 70' 2a 36 31 .10 48 52 56 90' r00' I t0' t20" 69 77 71 83 69 78 87 il a2 9oRH 30 35 15 50 55 60 65 1l '12 70 13 75 1i 80 90 Tzble S-2 11 18 20 23 26 2L 29 35 37 J3 13 15 23 31 4tJ 50 67 77 L7 25 5.1 !i0 19 27 29 31 33 34 36 38 83 95 101 85 93 103 20 22 24 25 17 26 18 28 52 57 69 45 55 70 73 47 57 76 60 62 68 78 88 96 105 i2 /-l 80 91 108 34 i4 63 73 a2 93 100 102 36 37 55 65 75 84 95 104 r13 6/^ 77 8t- 97 107 117 4{ 42 47 89 98 110 Dew Point Cakuklion Guide 5.6.3.8 Wind Chill Computation The wind chill temperature is a measureof"relative discomfort" due to combined cold and wind. It is the perceived temperature, due to the noisture evaporation ftom the skin that is erposed to the open air-it'GeIs" colder in a high wind than it does in calm air. lt was de veloped in 1941 by PauI A Siple and Chaies E Passeland is based on physiological stud ies ofthe rate ofheat loss for various combinations ofambient temoerature and wind soeed. The wind chiJl temperature equalsthe actual air temperature *ben rhe *ind 'peed n a mph or less.At higher wind speeds,the wind chill temperature is lower than the air temperature and measuresthe increasedcold stressand discomfort associatedwith wind. On November1,2001, the National Weather Service(NWS) implementeda rcplaccment Wind Chill Temperature Index. The equation for thn new indox is ns follows: lrind Chill (rF) = 1s.74 + 0.6215T a5.tSlvo tu, + 0.4275T(V0 16) whcrc T is thc air tcmpcraturc in "F and V is the wind speedin miles pcr hour The changcs madc by thc NWS improvc upon the Siple and Passeldata, which had bccn used since 1945. Table 5 3 will be used in thc softw-areto determine wind chill. The nature of the equation, with its fractional exponents, does not make it very conducive to a quick, inline calculation. Just as in the previously described dew point featurc, the table data will be induded in the software and used to "look uf' the wind clill basedon the read ing for temperature and wind speed. Ptujed Deael.Pheht wind Sreed in Mites Pq Hour (MPH) t0 ,5 20 25 30 35 40 34 2l 32 30 28 ?8 19 77 15 l4 27 13 9 6 29 16 3 tl 24 Tenp "F 40 30 20 10 0 -10 -20 -30 ,,t0 Tabfe 5-3 36 25 13 t -11 -22 -34 -28 41 53 57 7 9 19 22 35 32 45 58 --77 48 4L -74 --74 1 0 -t2 -14 26 -39 -53 -41 47 -69 80 -27 1 -15 -29 -43 -55 82 -71 84 NWS'200/ Sipleand Potselwnd Chi Coleldjon Cuide 5.6.3.9 Battery Health Baftery health can be as exotic as one choosesit to be.It can be as simple as measuring the voltage or as complicated as monitoring the charging curents and determining the battery's internal impedance changes.In most cases,an embeddedsystem is concern€dwith a simple requirement: "Is there enough voltage to operate correcdy?" This can be accomplished in most caseswith a resistivedivider, to scalethe voltage being measured,and an ADC. Alter nately, we could use the analog comparator peripherat in the AVR device, if w€ e inter ested in simply a "Go,4{o Go" reading. Resolution is not a really important issue for this measurcment in that we are only establishing a threshold to denote a problem. As long aswe set the threshold carefully, resolution 5.6.3.10 RealTime Real time is what we all live by In an embedded sptem, real time can be as simple as a periodic event or as complicated as a full blown clock and calendar-When we make measurements, and particularly when we log the measurements,a dock and calendar help enhance the useftlness of the data. If ln event occurs wherc the data looks out of the ordinary, in many casesit helps to know when it happened.This allows a human to link the data to a particular event or outside circumstance. There are several companies that manufacture real-tirne dock integrated circuits (ICs). Some are completely self-contained, like the Maxim DS1302 or DS1307, which maintain the time without the microprocessor,can be porvered for years on a srnall lithium battery, and usually interface to the microprocessor using a 3 wire SPI or 2-wne I'?C cornmunications linl. Most integrated circuits of this type reqne a 32.767KtI2 watch crystal for piopef opefatron. 283 244 Some microcontrollers, like the Atmel AVR, are designed to support a second crystal input source,such as a 32.767KH2 rvatch crystal, for the purposesofmaintaining rcal timc withrn the microcontroller without an ertemal doct IC. As long as the processorhas power, thrs clock can be mdntained. There are even features that allow the orocessorto "sleeo." a mode ofoperation of very low power consumption.nearll stopped.and to be a*rke;ed by the timer in order to update the real time and then go ba& to sleep.In this weather monitor, the indoor unit will be powered 6 time by an external plug-in supply and backed up through power outages by batteries. The display wiJl alrvavsbe actil'e, so there is not much point in \leeping" the microprocessorto savebattery life. The outdoor unit, however, might pro6t fiom the use of the power-dov"n mode. 5.6.4 HARDWAREDESIGN,OUTDOOR UNIT Now that we have proven to ounelves that the project really is possible, we cm start designing the 6nal hardware. 81' using the block diagams, specifcations, and feasibility researchfrom the definition phase,we can quickly pull together the schematics for the hardware.First, eachblock ofthe outdoor unit is developed,arrdthen the blocks are combined together in one schematic. The outdoor unit is dcsigncdto bc completelywireless.A 900 MHz transmittersendsthe collccted information to thc insidc unit every second or so. The unit is battcry xnd solar powcrcd, with thc idca that the sun rvill power the unit and charge the battcry by day and the unit will run completely from battery at night and on cloudy days. Low power consumption devicesare utilized for measuring the prrameters of temperature, humidity, wind speed,wind direction, and rainfatl. The 900 MHz transmitter is powered up only to sendinformation, thus consening power-The battery/solar-panel voltageis monitored by the microprocessorsuchthat the "health"ofthe power systemcan be reportedto the indoor unit. The schematicdevelopedfor the outdoor unit is shown in Figure 5-11. Specificportions arediscussedin the following paragraphs. Wind SpeedInput The r-ind speeddetectot as mcntioncd carlicr, is a magncticalll activatedreed-switch arrangement.Each time the ancmomctcrturns, a magnct is brought into proximitJ'ofthe switch,and thc switch is ctoscdfor thc duntion ofthe prcsenccofthc magnct.Thc problcm with mechanical switches is s-rvitchbounce. Since the input from the anemomctcr is going into a counter, it r.ould be very possible to get many more counts in the counter than there were revolutions of the anemometer The passivecircuitry incorporatedinto thc outdoor unit hclps to rcducc the possibilityof "extra'counts.The reed-srvitchis pullcd up with a resistorto Vcc (5 V DC) so that a TTLlevelinput is arailablefor the microprocessorA seriescapacitoris usedto colLplethe signal into the microprocessor The pull-down resistor located at the microprocessor'sinput, n combinationrvith the intern'a1protectiondiodesrvithin the AVR, providesa pulse-shaping network. As the reed-switchcloses,a nafow pulsc is gcncratcd at the Timer 1 input, ProjectDe,uela?nent 285 o J 3 s 33$ä3ääB arsp€pde$€3 $FF$$$FFEHFFF o c = ü E ! e sgäeE I g !0 tt n6 enough to causeit to count one pulse.The RC time constant ofthe pull-down resistor and the seriescapacitor allow the signal to recover slorvh enough from the first edge to not pass the switch bouncebut fast enoughthat the pulsesare not missedLnhigh wind conditions. Rain Gauge Input The rain gauge input is mlldll' fltered as well. Since rve are primarily concerned with the level (on or offJ at the nicroprocessor input, the main purpose ofthe 6lter is to eliminate noise and to "clean up" the signal coming from the reed-switch within the rain gauge. 900 MHzTiansmitter Thc 900 MHz transminer is an off the shelf F[4 transmitter module bv Lin'< Technologies.The TXM900HPII module supportseight different channelsin the'portable telephone" band. A DIP switch is used to selectwhich channel rve wish to use, ,llowing us to move the radio frequency away from that ofa local portable phone or interfering signals. The transmitter supports a power-dorvn feature that rvill be used to conservepowet because the outdoor unit runs fron battery and solar power The input to the module is the USART TXD signal directb from the Mega16. A 3.9K re sistor is used to prevent overdriving thc modulation input ofthe transmitter, which would causeit to "over modulate."The maximum modulation voltage (per the device specification) is not TTL; it is only about 1 V AC. The input of the module has a fairly low resistance. Some e4crimcntation proved that 3.9K gave the best performance with our system. Over modulation forces the ünnsmitter output to srving outside the proper FM modulation 'heär" range, which rvould cause both the receiver to not the transmitted signal and the trxnsmitter to generate unwanted R!- interference. Power Supply The powcr supply is preqv bxic. You rvill note that there are actually two 5 V supplies, one lor thc radio and one for evet thing else.This is done to reduce the arnount of digital norse lrom the processorto the transminer, asweII as to lower the amount of conducted RF from the transmitter back into eve4.thing else.The baftery is ä 12 V 2200 mAn, gel-cell gpe unit. These are ertremely rugged and rechargeable.They are considereda zero-maintemnce qpe ofbanery The solar panel is diodc couplcd into the qvstem such that on a sunny day n w l not only completely power the outside unit but charge the battery as rvell. You may also note that there is no current limiting between the solar panel and the system.The solar panel has a limited cunent capability due to its high internal resistance.Adding more resistancewoul.l sinply reduce the charging rate of the battew as well as the solar panel's contribution in runmng the s)5tem. s.6.5 SOFTWARE DES|GN,OUTDOOR UNtT Designing the software is rcallyjust planning out how the software rvill tunction. When the design ofthc software is complete, we have a list of tasks and their priorities and a set of florvcharts describing holv the tasks are tied tog€ther Ptujerr DeaelaPnent The software in the outdoor uniq by description, could be considered somewhat straight forward. The basicconcept is to collect the data and send it to the indoor unit. It is not qui te that simple, but it is more basic in many respectsthan what is going on with the indoor unir and is therefore a good place to get started. The task list in order oftop priority to least priority is as follows: l. Readthe wind speedcountifromTimer L 2. Updatethe räin gaugestate. 3. HandletheADC,staningconversions andstoringresulLs. 4- Formatandhandlerhe databeingsemto the tmnsmider. These four tasks are all handled on an interrupt basis.The only tasks left for the main operating loop ofthe software are to calculatewhen to send information to the transmitter and to put the informntion into a buffer for the transmrner. Figure 5-12 shows a basic flow diagram for the outdoor unit software. Note that there is a main process and four interrupt or erception processes:one for thc rain gauge interupt (INT0), another for sampling the temperature, humidity, wind dir€ction, and voltage readings (ADC), another for USART transmissions (IJSART_TXE), and another for sampling the wind speedtimer (Timer 1) and initiating transmissions(TMRO). The basics of the actual measurenents have been covered in the description ofthe hardware. The ADCs that ,re built into the A\.R measure tJ-retemperature, humidiry, and battery health. Timer 1 sampleswind speed.INT0 is used to keep track of rainfall. The telemetry is even kept simple by using the USART ofthe AVR such that standad I/O routines could be used 'light out ofthe box-" 5.6.6 HARDWARE DESIGN,INDOOR UNIT Now we repeat the design processfor the indoor unit- When the hardwrre design is done, we will have frrll schematicsfor the irdoor unit, as shown in Figure 5-13. The indoor unit has a 900 MHz receiver module for gathering bformation from the outdoor unit. The indoor unit comprises the samebasic power supply, microprocesso! tem perature sensing,and humidity sensing as the outdoor unit. The additions of a barometnc pressuresensor,buttons, LEDs, zbeeper, a 32.767KH2 watch crystal for a real-time dock, and ar LCD display really set it functionaly aprrt ftom the outdoor unit. There is no battery-charging slstem on the indoor unit, and the 900 MHz receiver is left active all the time so that the outdoor unit r€ports are hemd. The input power,6attery volt age is monitored so that the indoor unit can report a low-battery condition. 900 MHz Receiver The 900 MHz receiver is ar off-the-shelf FM receiver module by Li*x Technologies. The RXM9O0HPII module supports eight different channels in the ?ortable telephon€" band. A DlP-switch is used to selectwhich channel we wish to use,allowing us to move the radio frequency away from thxt of a local portable phone or interfering signals.The output from 288 Setup VO Pons, Timca, UART TMRO Timerl Sct Flag, RETI UART Disable liansftit Figure 5-f2 Flag Bas'rSofu'lorcFlo\rhocodnoot Unit the module is connected to the USART R)(D signal of the Mega16. A 1K resistor is used to provide a small amount ofRF isolation from the microprocessorby reducing RF currents that may be passing ftom the microprocessorback to the receiver-These currents are a result of the capacitance that appears on all the inputs of the microprocessor The resistor works with this caoacitance10 form a simole filter network. Prajett De,uelofm ent X i€ Yd"E =o g AA[ [ gg Fl E :a -' sq E s E d F"lri [-f-r#'t """1_ 1" - 'ü-1" 81" 1l = t,!; 5 Caü tE .ipl o I i H 2< IFE -; tl !t Eqie e69e :3:! E._(,J^c--r-aMÄ----J !-------rrH $3 dd"l"l,l, -t'"'"'l I 4 g o0 tt 289 290 The RSSI output of the receiver providcs a signal süength indication. This output rs processedand lights an LED to indicate when data is being received from the outside unir. (The LED may also indicate interfercncc and can be helpfin when selecting r channel.) This processedRSSI signal is also used to "quali$" the data coming in on the USART indicatethat the datais ralid, notjust noise.Spuriousor atnosphericnoisecould apper to be data. It would bc lcft totally up to the software to discern what is signal and what is noise. By creating an "RF detected" signal, REDEI we can use an intemrpt as a gating signal to cnxblc thc USART and lower the anount of software overhead required to decode the messagcsfrom the outside unit. Power Supply Just as in the outdoor unit, the power suppll'creates two 5 V supplies, one for the radio and one for cver).thing else.This is done to reduce the amount ofdigital noise from the processor to the receiver.The banery is a 6 V pact consisting offour AA alkaline batteries in series. The off the shelf power supply is diode-coupled into the sptem, ,llowing instant switching fron power supply to battery backup in the event ofa power outage. The LCD backlight is driven direcdy from the wall supply.Thc bacHight rcquircs too much current to run fiom the baftery, and it consumesenough curcnt to produce a large amount ofheat in the regulators.Therefore, we opted to drivc the backlight directly and blpass all ofthese issues.In the event ofa powcr failure, the unit will continue to operate (on battery porver), but the display bacldight will be out, making the display harder to see-we can shine a flashlight on it if wc nccd to know what it sa1s. 5.6.7 SOFTWAREDESIGN,INDOOR UNIT The indoor unit has two basic functions: collcct and convert data, and interlace with a human. The collection processis fairly straighdorward in that the indoor unit measuresthe indoor temperature, humidiq., barometric pressure,and battery health on its own ADCs in exäcdy the same manner as the outdoor unit. The outdoor parameters of temperature, humidiq,, rainfall, wind speed, wind direction, and banery health are collected in the same units asthc indoor unit (ADC counts,timer counts,etc.). The toughest part to developing the indoor unit sofiware is defining the human interface. Referring to "Operational Specification" in Section 5.6.2, "Dcfinition Phasc," this wcather monitor uses a four row by twenty column LCD and an xrangcmcnt of thrcc buttons. A 4X20 LCD may seem like a lot of room for information, but it can quickly become limir ing. In this s1'stem,all four lines are used to display parameters.The parameters are displayedin groupsofthree, as shown in Table 5 4. 'ltmpflture Outdoor BarometricPress.(^, v, -) R.infal this (lt, D, xI, Y) -fable 54 Timc (" flslcs PorcneterTtiods to 8€ D,:D,oyed $onds) \lÄnd Chill (Outdoor) wind Dire.tion,' & Head. Dew Pornr(Oüdoor) Date Ptuj..t I 6 B 5 0 3 o Lorv F 5 l I 8 5 5 D 0 4 3 F o 5 }I P H o 5 5 I 4 5 C 0 3 3 4 5 N N E D P I 2 3 F 0 I 0 8 9 c SET Figure 5-f4 o D.!etafhehl F o RX UNITS/+ SEI-ECT/- Exanple lndoot DisployUnitLCD üd Button layout Figure 5-14 shows an example layout for the LCD, LED, and buttons for the indoor unit. The button tunctions are SET. tiNITS/+. and SELECT/-. The SET button allows the user to set the time. The UNITS/+ and SELECT/- bunons increaseor decreasethe tirne or date component, respectively,and the SET button takes the user to the neal component until all have been set. Each time the user pressesthe INITS button, the curent units will switch from imperial to metric, or vice versa.This allows temperature to be viewed in "C or 'F, and wind speedin mph or kph. The SELECT/- bufton ,llows the user to view the rainlall in inches-this-hour, inches-this-day, inches-this-month, or inches-this-year. There are many possible alarm or alert conditions that a weather monitor like this could detect. Temperatures that are too high or too loq extreme wind and rain, high indoor humidity that could damage fruniture or equiprnenq and sudden large swings in barometric pressure that could indicate a storm is on its way. Table 5-5 shows some possible rarning/alert conditions. For the purposesofthis ter1, these warnings go a bit beyond the scopeofwhat we are trying to covet but these messageswould make a geat additional feature ifyou choose to imple mcnt them in your weather monitor. For our weather monitor, we will key in on a couple of basic s)stem erors that can prevent the monitor ftom performing correcdy: . Low bätteryconditions, indoorsor outdoors . No data€ommunications fromtfie outdoorunit An LED indicator is located near the display to sknal a detected low-batt€rT or low-voltage condition on the indoor unit. Whenever a low-voltage condition appears,software will flash the LED until the SET button is pressed-This will inform the user that during a power ourage the bafteries were found to be lorit is time for a change.The user could put in new 291 292 High IrdmrTmp Hish OutdoorTemp High Ind@r Humidirt High wind Alc.r High Rainfal Alcrt Lw Table 5-5 Batt Outd@i / essdges Possibrewsrdng/,qlen batteries and pressthe SET bunon to dear the eror The batteries can be checled at any time, simply by unplugging the power supply ftom thc unit. This low-voltage detection can also be used for an inte\ent shutdown ofthe system,in erther the outdoor or the indoor unit. Ifthe voltage is detected to be below nomal, data such as the accumulated rainfäll can be sar"edto EEPROM, arrd then the unit could simply hold in a loop waiting for the power to disappearcompletely or to return to an acceptablelevel. Handling EEPROM storage in this as needed manner also preservesits life, becausecontinuously writing to EEPROM will evennnlly lead to its fanure- As discussedin Chapter 1, the poteotial for failure is due to the way that EEPROM memory itself is constncted, a function ofelectro-chemistry- In many cases,this memory areawill have a rating of 10,000 or 100,000 write operations, ,nßaim rn. A low-battery condition on the outside unit will eventua[y lead to no data reports from the outside unit. In this case,the low battcry LED indicator on the inside unit will be turned on solid until the outside unit voltage goesback up to normal- When the outside unit voltage goes back to normal, the LED will go back off. When valid data has not be€n rcc€ived from the outdoor unit within 15 seconds, a "No Communications" error exis*. This could be due to the outdoor unitt power going away, or a lengthy period of RF interference. While this condition exists, all outdoor-related parameterswill be replrced with question marks. For example,wind speedwould read: ??? MPH 5.6.8 TEST DEFINITION PHASE The test defnition phase ofthe project oudines specifcally how wc iotend to test both the individual piecesofthe project and the complete project. Some measurementsare very easy _::::::!:::^:: to test, rvh;lc others requne much more vork and creativiqr Somc may also require writing softwarc for the microconrroller The test definitions lor rarious parts of thc projcct are sholvn below: Wind Direction Input: 0 to 5 V DC through a 10K ohm potcntromctcr. ExpectedResults:0to 5 V input to microcontroller Method: Apply different voltages to the input through a potentiometer to simulate a *.eather rane and measurethe \.oltage input to thc microcontroller rvith a rrcltmeter. Wind Speed Input: 30 mph u'ind-might requne a friend, a reliablc method of transportation,md a calm day! ExpectedResults:75Hz signalto the microprocessor Methodr Causethe anemometerto be blorvnat a knorvnratexnd measurethe pulsetnin to or the microcontrolleritself. thc microcontrollerusing a frequencl'counter,an oscilloscope, You might needto unite softlare to count the pulsesand transmit them to the indoor umt for displayifa portablemethod of counting the pulsesis requircd.The selectedanemometer lor this projectis factorycalibratedaad producesa singlepulseper revolution.The output is approximatcly2.515 H'zlrnph. Onl,vninor adjustmentsmay be rcquired. Rain Gauge Input: One cup (8 oz.) ofrvater ExpectedResults:A representative numbü oftransitions presentedto the microcontrollcr input. Method: S/atul1pour the rvater j nto the rain gaugeand, using a counter or thc microcontroller itseld,count the transitions. Thc RG-T transitions every 0.01 inch of rainfall, so a counter shouldindicate722 lorv to hjgh transitions,or 1444changesofstate.You mar nccd to wrire sofnvare to count the transitions and transmit them to the indoor unit for displar: The selectedrain gaugefor this projcct is factorl cdibratedand shouldneedno adjustments. Air Temperature Inputr Ice watet room temperature,rvarm hands. ExpectedResults:A rcprcsentadleloltage presentedto the microcontrollcrinput. Method: Ptacethe NTC deviceon somelongwire leads,24inchesor so.Sealthe deviccrn a smallplasticbag (removeasmuch aira possible).Placethe devicein ice rvater32'F (0'C); after a minute or so,2.39 V DC shouldbc prcsentat the microcontroller'sinput. At room temperature,70'F (21'C) a r.oltageofappronmatclv 3.3 V should be present. 294 Barometric Pressure Input The atmosphere. Expected Results: A rcpresentativevoltage prcsented to the microcontroller input. Method: Using another barometer as a refercncc (or the local weather station if it transmits continuously through the TV), measurethe voltage input to the microcontroller with a voltmeter-O V DC represents28 inHg, and 5 V DC represents32 inHg. Relative Humidity Input: The atmosphere. Expected Results: A representativcvoltage prcsented to the microcontroller input. Method: Using another humidistat as a reference,measurc thc voltage input to the microcontroller with a voltmeter and compare the values { V DC represents0% RH and 5 V DC represents100% RH. The selectedhumidistat for this project is factory calibrated and shouldneedno adiustments. SystemTest for Complete Project The o,:tent ofthc system test definition wiII vary according to the end user ofthe project. If thc weather station project were to be destined for home usc, the test might be no more ertensive than comparing the weather statior readouts to the local weather station to seethe results are "about right." On the other hand, ifthe project is for commercial usageor for a customer, more extensive testing is required- In this case,it would be appropriate to use tcmperature and humidity-controlled chambersto run thc outside and inside units through thc entire range ofweather conditions and record thc rcsults. For instance, it would be appropriate to test the tempemture reading at, say,every 5'F and plot the results to ensurethat the unit meets specifications over the entire range of temperature. Each ofthe weather parameters would be tested in the samethorough maaner and the results graphed for presentation to the customer. Whatever thc extent of the tests imposed for system tes! the intcnt is the same:to give the end user conndence that the unit is performing up to specificxtions as set down during the definition phasc. 5.6.9 BUILDANDTEST PROTOTYPEHARDWARE PHASE The project hardware is completely designed, and the expectedresults ofeach section ofthe hardware are speciEed.It is now time to build the hardware. Aftcr thc hardware is assem bled, the tests from the previous phaseare executed.This section bricflv discussessornereal life methods of crecuting the tists and measulng the results.The qoftwarr requircd to e{ecute the tests is also discussed. Fundamental tests of the hardware are best oerformed with voltmeters and oscilloscooes. When an AVR microcontrolleris completelycrxed. all ofir" pins ue inputs,rrd it hai no tl Dnelo?nüt *Praje , impact on the surrounding circuitry. This allows for some basic checking of the hardr,rare functionality. No matter how good the software is, it can never make up for hardware that just does not work. Listed below are some step by step checls for both the outdoor-unit and the indoor unit hardrvare.This example method ofvalidation applies to many g?es of designs. Knowing for certain that the signals are as expected gready reduces the softlvare development and integrntion time, as well as the amount of time 1'ou rvill spend "chasing your tail" when things do not make sense. Outdoor Unit Checkout At | . Setthe labsupplyfor | 2V DC with a cunent limit of approximately one ampere. this point,no batteryor solarpanelshouldbe connected. 2. Connecta labsupplyto the batteryor solarpanelconn€ction. 3. Makesure thatVccandVcc-| are ar 5 V DC. lf the powersupplyis not correct,nothing will be quiteright" 4. UsinSa voltmeteiverirythat the BATTsignal(pin38 of the M€8a| 5) is approximately 3.8VDC. v€rit thatthe oütputof the hümidistat is a levelthatcorr€sponds 5- Usingä voltmeter, with the humidityof the room thatyou äre in-An ofüc€or classroom is typically20 to 30%RH.Whäteverthe percenEge is,yooshouldmeasure aboutthat percentage of 5V on the HUMIDsignäl(pin39 of the Megal6). 5. Usinga voltmeteiverirythat the outputof the tempemturesensoris a levelthat correspondswith the temperatureof the room that you are in.Theaverageotrice or classroom temperatureis about70'F (21'C),andthat shouldcausea voltageof approximately l6).lf you pinchthe 3.3Vto appearat tneTEMPsignal(pin40 of the l'4egä you shouldseethe voltagerise thermistorir yourfingerswhilewatchingthisvoltage, asyour body heatwarms the sensor 7. Connecttheanemometer andthe windvaneto the appropriate inputs. verit $ät the SPEED signal(pin2 of the Mega| 5) häspulsesof 8. Usingan oscilloscope, level(rTL level,whichis greäterthan1.3V for a "high"andlessthan | .5V adequate for a"low").Thesepulseswill existonlywhileyouspinthe än€mometer, so Siveit a whirll 9. UsinSa voltmeterverifythat thewlND input(pin37 ofthe Megal6)movesuniformly from 0V to 5V DC asyou siowlyrotate the wind vane.As you cross nonh,the voltage will iumpfrom 0V to 5 V,or from 5V to 0 V | 0. Connectthe räingauteto the approp.iäteinpur I l. Usinga voltmeteror an os€illoscope, verirythe MIN sisnal(pin l6 of the Mesal6).As you either tip the seesawassemblyby handor pour water throughthe gäuge,you f.om 0V to 5V DC andbäckagain. shouldseethe voltageofüe RAINsignaltmnsition 12. Usingthe test programlistedbelow programthe MeSa16with the followinSfuse bit settinss.These settings the properoperationofthe oscillatorandbrown-out Suarantee ns 296 detector usedto reset the microcontroller: . CKSEL3:o= | | 00,crystälOscillatoiBOD enabled . SUTI:o= l0 . BODEN= oN . BODLVL= ON . JTAG= OFF . OCD = oFF . EESAVE = OFF ' BOOTRST= OFF OuEdoor unit tesL + include <Mesa16.h> +include <stdio.h> +include <de1ay.h> nain (void) void { PORTC=oXoo; // DDRC=0x40; // USART Transnitter: // ÜsaRT Baud.ate: UCSRA=0x00; UCSRB=0x04, UBRR=0x19; üBRRHI=0x00; while (1) // porl selup C and on TX-POWER.. lurn on 9600, senal rest a Data, slream 1 stop, every No Parltv 1 second t delay ns(100); // pubsf ('uuusresEtQQQ\r' detay ns(500); PORTC_6 = !; alelay ns (500) ; PORTC.6 = 0; // a11ow power up tine ) ; transnit RF powe. // // waiL.. // RF Power nessaere off on l ll. Usinga RFsignal-streneth mete4a spectrumanalFer,or a LinxTechnologi€s beingtransmitted Note TXl4900HPll emluationkit wiü a rc, monitor the messag€s millis€conds.Transgo betw€€n transmissions for 500 thatthe RFenergyshould ofi second aparc missions shouldoccuraboutone Ptaje.t Deaeta?nent Indoor Unit Checkout At | . Setthe labsupplyfor 9 V DC with a currentlimit of approximately one amperethispoint,no batteriesshouldbe connected. 2. Connecta labsupplyto the wäll supplyconn€ction. 3. l4akesurethatvc€andVcc-lareat 5V DC.lfthe powersupplyis not corr€ct,nothing will be quiterighlSoundfamiliar? lt is stilltrue. 4. Mäkesur€th€ backliSht is lit on th€ LCD display. 5. Usinga voltmeteaverifythat d'€ BATTsiSnäl(pin38 of the Mega| 6) is approximateiy 2.8VDCis a levelthat corresponds 6. Usinga voltmeter, verifythatth€ outputof the humidistat you is typically20 to with the humidityofthe roomthat are in.An officeor classroom per€entage is, you measure about thät percentage of 5V 30%RH.Whatever the should (pin on the HUIYIDsisnal 39 ofthe M€sal6). 7. Usinga voltmeteiverjfythat the outputof the temperature sensoris a levelthat corofflceor responds with the temperature of the roomthat youare 'n.Theaverage classroom temperätureis about70"F(21"C),andthat shouldcausea voltageof approximately 3.3Vto appearat theTEI'4P signal(pin40 of the Megal6).lfyou pinchth€ you shouldseethe vokagerise thermistorin your fingerswhilewatchingthisvoltage, asyour bodyheatwarmsthe sensor. 8. Usingä voltmet€rto measure the CAL potentiom€ter wiper,setthe CAL potentiometersuchthat th€ wipervoltägeis 2,06VDC.Oncethisis set,measure the voltageat th€ BAROsi8nal(pln37 of the Megal5)andv€rirythat it is somewhatrepres€ntativ€ ofthe currentbarometricpressure. Remember that 0V DC atthe BARO daxthe signalrepresents 28 inHSandthat 5V DC represents 32 inHg.On an average readingshouldbe somewhere in the middle.This mightbe agoodtime to actuallycalithe bratethe barometer. Get a currentlocalbarometricpressurereadingandcalculäte voltagethispressureshouldproduceatthe BAROsignal. Adiustthe CAL potentiomet€r until you readthat voltaSeat the BAROsignal. 9. With the outdoorunit runningits test progiämasan RFsignalsource,checkthe REDETsitnalby monitoringth€ PxActive LEDTh€ RxActiveLEDshouldgo on for 500milliseconds andthenofr for 500millis€conds, againandagain.Verify that datais gettingto the processorby lookingat th€ RXD input(pin I 4) of the Mega| 6 with an oscilloscope.The waveformshouldlook something liketheTXD output(pin | 5) of the outdo0runit. 10. Usingthe test programlistedbeloq programthe Megal6with the followingfusebit guamntee settings.These settings the properoperationof the oscillätorandbrownreset out detectorusedto th€ microcontrolle.: . CKSEL3:o=l 100,CrystalOscillator,BOD enabled . SUT| :0 = I0 . BODEN= ON 297 798 . BODLVL= ON . JTAG= OFF ' OCD = OFF . EESAVE = OFF . BOOTRST= OFF Indoor unit TesE coale +include <Meqra16.h> +include <ale1ay.h> *define +define +define *defioe unsigned vo'd w! LcD B LcD Rs LcD Rw LCD PORT char tcD PoRTB.o PoRTB.l PoRTB.2 PORTC ADDR; /t LCD CoDrlo1 /T LCD DATA PORT :/ Lines */ *****/ Funcrions aalt(unsiqnao.ndr dälä) { tCD Rw = 0; LCD_E = 1; ICD_DOPTrcD_E - 0; tcD_Rfl // (daL- = 1; delay_ns(3); set wR actlve // raise d 0x0F); // // drop E prr därä oa po, E // disable // a1low I'rR alisptay tine to think ) void wr dlsp(unsisneal char alata) i LcD_Rl.j = 0; LCD_E = 1; LCD_PoRT= (data LcD E = 0; LCD E = 1,. LCD PORT = (data LCD E = 0,. // enable srite.. sErobe upper >> 4); // half of daLa // out to the display & 0x0F); // now, strobe Ehe love! half Ptuject De0eta?nent LcD Rw = 1; delay disable // ms(l); // allow vrire time for LcD to react ) void disp char{unsigned char c) ctlar flash t LCD RS = t; wr disp{c); LCD-ADDR++; J void disp-cstr{ünsignetl *sa) /' stlinq ilisplav t while ( rsa != 0) disp cha! ( *sa++) ; void init display(woid) t LCD_R!! = t; IcD E - 0; LcD Rs = 0; delay wr half sr praser // ns(50); (Ox33J ; half(0x33); wr half(0x33); vr ]narf(0x22) wr disp(0x28); wr disp{0x01); sr disp(0x10), | // This // rot These in // Enable // set cursor to nowe (insEead of alisplaY disp(0x06); // // sr disp{oxoc); // // cormands the nanufacture.'s the idternat dala 5x7 sheets- font shifE). to nowe !i9rht, set Ehe cursor the disptay noE shift off, Turns alisplaY on, cursor blinking off. ctrsor rnni i<0x5F; displav can ltre found // rr for (1=0x40; the sequence enables interface node 4 bj.t // // { sisnals infetlace node.. comaDd // i++) /äm to "00' and and E9 300 alelay ns (10) ; LCD,RS = 0; w! disp(i); alelay,ns(10); alisp-cha!(0); J LCD RS = 1; ] void clear_display(woid) { trCD_RS = 0; wr_disp{0x01) ; delay_ns{10); ICD-RS = 1; // cfeai alisplay and home cursor ] void nain(void) PORTB:0x00; DDRB=0x07; // outputs for LcD signals PORTC=0x00; DDRC=0x0F; // ouEpurs for LcD alata PORTD=0x00; DDRD=0x60; / / beepe. 32K C l o c k // Enable ASSR=0x04; init display( clear_display disp_csti () ; ( 'haloor // LED outputs TOSCI pin source: // ); and ioitialize clear resL"l i LcD displäy // print test nessage. P/ajüt rhile { De{eta?ne"t (1) if (PINA & 0xE0) // if any button P.essed. t P O R T D . 6= 1 ; P O R T D . s= 1 ; detay (s (1) ; P O R T D . s= 0 ; delay ns (1) ; // LOIÎ BATT LED ON PORTD.6 = PORTD.5 = // LOW BATT LED OFF I t t | | . Verit dr€ message "lndoor Teqt"äpp€a.son the LCD| 2. Pressthe UNITS,SELECT, andSETbuttons.The beepershouldsoundat approximately 500 Hz,andthe LOW BATTERY LEDshouldlighta! longasoneof the buttonsis pressed. | 3. Usingan oscilloscope, verifythat the 32 KHz oscillatoris runnin8by probingpins28 and29 of the Megal6. 5.6.I0 SYSTE1.,I INTEGRATIONAND SOFTWARE DEVELOPT4ENT PHASE. OUTDOOR UNIT The 6rst step in putting together the software for the outdoor unit is to define the unit op eration. In this case,a slctem decision can be made as to where the processingofthe actual data is to occur, indoors or outdoors. If the drta were processedoutdoors, then each of the parameterswould have to be calibrated, and common units,like "F or "C for temperaturc, would need to be deflred for the data that is to be transmitted- Rainfall gets a bit messyin that it basically takes forer.er,and the outside unit wodd have to know how long forever is. This thought processleads us to leaving the data collected in the most basic form possibte and letting the indoor unit do the conr,crsions at the end. Besides, the indoor unit has a clock and interfaces with the human anls'ay. So in this system the most basic units would be ADC counts, Timer 1 counts, and the state of the rain gauge and the weather vane. This data can be combined and transmitted as a packet ofvalues on a periodic basis.The transmitted period ofthe packets is not rcally cnt ical. There should be enough data to catch the peaks ofwind and get an accuratereprcsen tation ofrainfall. These are not panicularly fast moving parameten, but humans like to feel like they are being updated fa yfiequendy. For instance, a gical digital voltmeter offers a one second sampling rate. The only citical sampling that is taking place is the wind speed. 301 302 It is the time between readings that is important for calculating the mph of the wind. Even though it will be sampled quickly, an averageofthe readings is all that is necessaryfor an adequatewind speedrepresentation. One consideration is the banery consumption during the transmission ofthe data. It is during the transmission ofthe data to the indoor unit that the highest cunent requirements of the system are achieved.The duty cyde, or ratio of time active to time inactive, ultimately determines the averagecurrent draw on the power supply, whether it is the solar panel, the battery or both. The nart step in getting the software started is to define the inputs and outputs of the microprocessor that are to be used. This is a great way to get started, since another round of sanity checking gets performed on the schematic, and once the deEnitions are made, the need for constantly refeting back to the schematic is reduced. The definitions for the outdoor unit may appear as shovm in Figure 5-15. A reminder: comments following the #defne statements need "/* and "7 as delimiters. Once the pins have been labeled, the actual inputs, ouguts, and peripherals need to be configured. This is usually performed at or called fton t\e top of na;n). \n the initializatroo ' routine "ini r-avR ( ) (seecode in Figure 5-16), note thatTimer 0 is set to create an overflow interrupt. Based on a 4.0 MHz oscillator, the intemrpt will be issued every 4.096 ms. This real-time tick will be used to sample the anemometer as well as determine when it is time to transmit the data to the indoor unit. Timer 1 is configured as a counter to capture the switch transitions in the aflemometer to measurewind speed.INT0 is set to interrupt on "any chanqe", which allows each tipping ofthe seesawin the rain gaugeto be captured. The USART is configured for 9600 baud, 8 data bits, and 1 stop bit for the RF transmissions.The ADC is set up to convert at the slow€st rate, which is generally the best, and to generate an interrupt upon completion ofeach conveßion. PrNc- ? #define I'x cTs +define Tx PowER PoRTc,6 + d E f i N E W I N D S P E E DI N P V T P ] N B . 1 /* /r /* LransniLrer clear to sead */ p ower enable "/ EransniEEer */ anenoneter inpu! (Tinerl) + d e f i n e L A S T _ a D C _ I N P U T3 +def ine ADC_VREF_TYPE0x40 u n s i g n e d i n t a d c _ d a t a I L A S T _ A D C _ I N P U T - F I R S TA D C I I , I P U T + 1 ] ; *dEfiNE +define +define +def ine TEMPERATURE HUMIDfTY BATTERY i,lTND_DIRECTION adc daratol adc-alaEalll adc_alatat2l adc_alata[3] Figure s- | s üonple Defintions,OutdootUnit llo /i /' /* /* analos analos analos analos chan chan chan chan 0, f. 2, 3, int int int int */ ]/ */ */ Plajüt #define #define +define FTRST_ADC_INPUT 0 LAST_ADC_INPUT 3 aDc_vREF TYPE 0x40 /t A/D conwerrer t rnput/ourput /* */ Ports initialization DDRB=0x00; /* Port c */ PORTC=0x00; PÖtL /* D */ PORTD=0x00; DDRD=0x02; */ Tine!/counrer 0 inllializalion Clock soulce: Syslem Clock Clock vatue: 62.500 k$z Mode: OutpuE Conpare o.0 o. pur : Dis.onne.rcd TcCRo=0x03; TCNT0=0x00; /* /* /* /* ' /* /* /* /* /* /* Tiner/counter 1 initialization clock soulce: T1 pin Rising l,Iode: ourput Conpare oClA output: Discon. OClB outpuE: Discon. Noise Cancele.: Off - p.. .dpLurc TCCRlA=0x00; TCCRlB=0x0?; TCNTlH=0x0 0, T C N T l L = 0 x 00 ; OCRlAH=0x00; OCRlAL=0x00; OCRlB$=0x00; OCR1BL=0x00; ' /* /* Tiner/counter cLock source: Figure 5-f5 on Fdllinq '/ Ealge */ '/ Edqc 2 lnltlalization systen clock */ OuttlootUniLIO lnitialization(Continues) Deae/a?meht 303 304 /* Clock value: Tiner 2 sLopped /* Mode: Output Conpare ' oc2 oulpuL: Disconnected T C C R 2= 0 x 0 0 ; '/ TCNT2=0x00; */ (s) initialization /* External Interiupt /* INTo: On /* INTo Mode: any chanse /* INT1: Off /+ rNa2. aff cIcR l=0x40, MCUCSR=0x00; GIFR=0x40; /* Tiner(s)/Counter(s) TIMSK=0x01, InrerrupE(s) inirialization /* uaRT iniciatization /' Comunicacion Parameters: 8 Däta, I Stop, /* UART Receiver: Off On /* UART TransnitEer: 9600 /* üART Baud rate: UCSRA=0x00; UcSRB=0x44; UBRRH=0x00; /* /i AnaloS Conparalo. initiatization AnaloS Conparalo.: Off Conparato. /* Analos ACSR=0x80; SFIOR=0x00; I4put CapEure by /* ADC initializalion frequency: 3I.25O kaz */ /* ADC Clock Reference: Avcc pin */ /* ADc volrase ADMUX=FIRST ADC INPUTIADC VREF TYPE; /* Watchdos Tiner /t Watchdog Tiner WDTCR=0x0F; enable /* clobal +asn("sei') initialization Prescaler: OSC/2048 interruptss ) Figure 5-f6 OutdootUnit,llo In ializotion(Continued) ,/ r/ Projeü Deeelo?ment Temperature, Humidity, Wind Direction, and Battery Health Tempeüture, humidity, wind direction, and battery health can all be measuredin the background using an interfllpt routine servicing the ADC.Thevalues ofthe array"adc daLa" a-re automatically loaded. The def,nitions, "tmreenatunr", "EUMrDrrY", "wrND DrREcrrQN", and "earrsnv" are aliasesto help us remember which channel rcpresentswhich signal.The general-purposeÄDC interflrpt subroutine is listed in Figure 5-17. Rainfall Rainfall is handled by simply keeping track ofthe strte of the I/O Pin. Using an interrupt in this manner is probably a little overdone, but therc are still some questions about the "rcal world" operation ofthe rain gauge,and this is a good way to leave some options open. The INT0 function ofPIND.2 has been setup to generate an intermpt in "anv chanse". This means when the signal at PIND.2 changes fiom high-to low or low-to-high, the isr ( ) " (shown in Figurc 5-18) gets called.In this interupt serviceroutine "ext-int0 "rain the character state" is set to reflect the rain gauge input interrupt routine, asI rei /'AlD.onJe AD. _t\öur o LAST ADC INPUT l +define +dEfiNE ADC VREF TYPE OX4O ADc 'NPUT FIqS- ÄD.-INDUF-ll igr6o 1nr do. de.-lLAschar inpur index=0; 60ö A +define +define #define +define /i analog analog analoq analoq TEMPERATURE HUMIDITY BATTERY WIND DIRECTION aDc interrupt se.vice { aDc convelsion result '/ */ /: Read the /* if t/ SeLecL next ADc input (++input index> (LAST aDC-INPUT-FIRST input index=o; ADC INPUT) ADC INPUT'I ADC VREF_ICYPE; ADMUX=iNPUI iNdEX+FIRST r/ lhe next aDc conversion /* Starl A D C S R A= 0 x 4 0 ; Figure 5-f7 0, 1, 2, 3, routine inPu! s'.nr'-9 IADC INTI woid aalc isr{void) interrupt chan chan chan chan Ercnple FrceRunningADc fntemrplSentceRour,ine int int inL inL */ "/ */ */ 305 306 rdafjnp cha! FA.J\ raln /a Ex!e!na1 .!e r -pt tNPUf staie; PtND.2 cudent /* /'räin staLe of gdug. rain :"p1. gauqe as a char */ */ 0 service routine void exr inf0 isr (void) InterrupL Erl--N-01 { if (RAIN_INPUT) rain_state else rain state = 1; = 0, /t /a /* keep chanqe around in for tater transnission t/ unit... a valiab1e to indoor */ */ ] Fisure 5-f 8 RainGoW lnputlntqftuptHondtel "nAIN rNPur", which is the pon pin itself. Earlier, w€ discussedthe possibilityof s\{itch bounce.In the caseof the rain guge, becausethe seesawmovesso infiequently, and becausewe report to the indoor unit the stateofthe actualinput pin, the chanceof actually havingan enoneousreadingis negligible. Wind Speed In the previoussanitychecks,we decidedto useTimer 1 to count the wind speedpulses. Samplingthe count on Timer 1 is handledwithin the Timer 0 interrupt routrne.As mentioned previously,the Tiner 0 interupt executes €very4.096ms.Ifwe reducethe sampling rateto er.,erysecond,at leastuntil v/e canobtain actualdatafrom th€ anemomet€r,the collectednumberin Timer 1 would effectivelybe five timeslarger To obtain a samplerate of approximatelyone second,we will needto take a Tim€r 1 readingonceevery244 passes through the Timer 0 inteffüpt routine. (1 second: 4.096 ns/pass) = 244.1 The one-second interv'al also provides a method oftirning when the RF telemetry is to take place. Once the samplesare taken, a flag "RF I'x rime", asshowa in Figure 5-19, is set and ts picked ry ia nain) to initiate a transmission. RFThlemetry The RF telemetry is handled in the nainq function. The flag "RF rx rime" is used to signal when data is to be sent to the indoor unit The data is prearranged into packets. Packetsprovide a structure to the data that makes it easierto the receiving device to decode. When the data is organized in this fashion, the receiving device is able to predict what kind ofdata to expect and how much. The format of the data packet to be sent is as follows: UUUSttt. hhh -wv. ddd- ssss - r -xxxxrQQQ where tr is the temperatuteADC reading,bhb is the humidity ADC reading,vtv is the batteryvoltagereadingat the ADC, and //1 is the wind direaion. The datafor the ADC Project Deuta?nent +define LND_SPEED_INPUT .-sigr-d i dind_spccd; FsL päss; in- Ä:rd /* Tiner in-.rrupt */ (Tinerl) inpuc /* anenoneLei /' averdge pdss .ount beao'e wind speed sqmple PINB.1 /r */ 0 overflow intefiupt service routine ( v o i d ) ' o v F l v o i d i m c r 0 o v r _ i s r lTrr40 if (++vind test pass > 243) /* passes befo.e +=TCNT1; reaal(accunutaEe) lhe widd speed sanple { wind_speed TCNT1 = 0; pass {ind test wind speed /= RF_TX_Tine /* /t reset counEer fo. riner next value */ */ sanple. = 0, 2; = 1; /* /i sinple average rime to of Lransmit two.. */ anorher packet */ ] Figure 5- | 9 Timet 0 lntem)pt Seflice Routine readings are each sent as 3-nibble values, becausethe ADC ralues will be between 0x000 and oxFFF. This savestransmissior time by reducing the total number ofcharacters sent. The value ssrsis the Timer 1 reading, / is the rain-gaug€ state, and rrurc is a checksum made up of the sum ofthe data itself The values are all in hexadecimal. The preamble (/{/Uis used to provide a somewhat s}.rnmetdcal bit pattern as the pa&et is starting. The ASCII code for the lener "U" is a hexadecimal 55. This helps the modulation chamcteristics ofthe transmitter and is easyto detect at the indoor unit. The do[ar sign ($) is used to indicate the actual start ofpacket. The dots (.) are used to delimit the values such that they can be easily decodedby r[\e $eß,f0 fitnction in the indoor unit The asterisk (*) is used to indicate the end ofthe packet, and the Qgq is used as a postscript to again provide a somewhat synmetricat bit pattern as the packet is ending. The ASCII code for the lettel "Ql is a hexadecimals1. The checksum is used to check the validity of the information that is receivedby the indoor unit. Checksums come in a mriety offorms, such as the ones complem€nt ofthe sum ofthe data, the twos compl€ment of the sum of the data, CRCs (Edi redundancf clecLs),and so on. In general, a checksum is the surnming or combining of the data withio the message such that by utilizing the values contained within the message,long with the checksum,the receiving device can test the validity ofthe content ofthe message.Iftle checksum does not match the sum ofthe data received,the data can be rejected-It is rot uncommon in a wireless system to have RF interference or amospheric conditions alter the messag€.\tr/hat is important is that we do not calculate the weather readings with bad data. 307 308 So, using a data packet ofthe form UUUSttt,hhh. wv. ddd. ssss. r. xxs*aaA with a temperaturereadingof 70! a humidity readingof50%, a batterylevel of 11.5[ a wind out ofthe westat a speedof5 mph, and no rainfall, the packetof dataviewedwith an ASCII terminal might look like this: . F F -0 0 3 2 .0 - 1 0 9 5 ' Q Q Q u i r u 9 2 7 68. 0 0- 2 E E 2 The actual values were calculated using the conversion factors for each parameter being measured.Since the example temperature is 70"8 its valu€ to be transmitted is calculated as follows: Proportion of ranqe used . ?50 counEs in Entire 1t2 counts the ranse range (to account for the 0-84 v = ADc output offset) which computes to be ?0 - (-40) . 140 - 150 | t12 - 6l0.rro.ouncs \ 216.e ca-4.s (-40) Thereforethe temperaturevaluewithin the packetis Ox276asshownbelow: u u u s 2 7 5. 8 0 0. 2 E E . 2 F F0. 0 3 2. 0 . 1 0 9 5 * Q Q Q As in other examples in this t€xt, interrupts are us€d to actually send the characters out of the USART. As shov,.n^ Fiq'ne 5 2ß, ? tcba4) has been redefined to work with this intemrpt sewice mutine, and the "*define AT,TERNATEpurclrAR " is used to signal to the standard library that this ?uftharq rs to rcplece the built in tunction. TX_BUFFER SIZE 4a +define cha. Tx Buffe. [Tx BUFFER SrZE+1]; char char Tx countef,. Tx Rd rndex; '-ä- Tx wr /* Inoex; UART Tlansmirter /{ /* U A R ' I 'I ' r a n s m i t c e i intellupt inlelfupts tusÄRT_Txcl void i if {Tx counter != 0) selvice UART TransniCle! incarrupr routine selvice '/ uarE_Ex_isr(void) t Figure 5-20 Exomple, lntenpt DtivenUSART Tnnsnission(Continues) Buffer */ -ouL:- e Proj.ct Deutofnent == 1) if(fPrinedIL I = 0; fPrinedIE if(++Tx_Ral /* /* rndex Tx_Rd_Inalex only send a cha! tradsnision, then > TX BUFFER SrZE) /* Lest and wrap = 0,. TX Counter--; /r keep tsrack of if one don'E in */ buffer send Ehe */ the pointer */ lhe counter */ t if (TX-CounEer != 0) { UDR = 'Ix-Buffer if [TX Rd hdex]; /* orhelwise, send char out r/ port (++Tx_Rat_Index > TX_BUFFBR SrzE) /* test and wrap TX Rd Index = 0, Tx_Countser the pointer */ the counter r/ ; /* keep track of ) J J a character to /* Wlite woid putchar(char c) t = 0; char stuffit while (Tx_counter /* if > ITAITl ir {-z_w._r-der Tx_ltr_Index wr (TX_BüFFER SIZE /* hdex++l - UART Transmitter uf fer (Tx_CounEer == 0) = 1; sluffit Tx_Buffe.lTx the if is = cr 1)) qetting L'uffer /+ TX BUeFERsrzE) = 0; fullt empty, jan I */ setsup fo. the char in /r w/äp thc TX-Counler++,. Figure 5-20 */ buffer Exompie,,nterruptDrivenUs4{Tlrans,'.'ission (Contitues) */ inEerrupt Ehe buffer,, po:-.er i */ 309 3t0 /* do we have /. this chd' to "Prime s!cr.s lhe ,, - t!ö pump"? .p... . ] _ALTERNATE_PUTCHAR_ /* SEandard Input/output <stdio.h> +include Figure S-20 */ functions Example,lntempt Diven USANTnTßnirrbn(Connnued) flag and perThe flJnction nain) is\tstedinFgate 5 21. nain, tests the "RF rx-rine' lorms the telemetry operation. This operation includes computing a checksum, formatting the data into a packet, enabling the RF transmiüe! sending tie packet, waiting for the transmission to complete, and powering down the RI transmitter The example shown indicates the intended operation. There may be timing considerations to be taken into ac count when enabling and disabling the RF transmitter Note that the watchdog timer n reset periodically in the mainq totine.The watchdog witl help the outdoor unit to con tinue prcper operations during periods oflow battery power, or any other situation that may lead to an erratic electrical or operational condition. As mentioned previously, the definitions, "TEMPEFATURE",funMrDrry", tdrND_DrREcrrori', and "BATTERy" aft aliasesto help us remember which channel representswhich signal. In Figure 5 21, you can seehow they are treated as vadabl€ names. /* PINC.7 {define lnsign-o +define +define +define +define void Tx PoiiER cna! p-ckeEtTx TEMPE|ÄTURE HUMIDITY BATTERY wrND DrREcTroN transmitEer / B-eFER SrTEl; aalc adc adc adc daLa[0] daLall] alata[2] alara[3] /* /* /* /* rF analos analos analog anatos nain (void) t ini!-aVR( ) ; Figure s-21 clea! !o send PORTC.6 Ptopose,l noin1, fot drc OutdootUnit (Continues) d-.- chan chan chan chan o"'l- 0, 1, 2, 3, */ int t/ int lnE',/ rnE r/ ' */ Plaje.t D.aeto?neit { if { /* /* (RF_Tx_Tine) disable interrupts tso prewents dara fron durlns the formattins of Ehe packet *asn('c1i') checKsun checksün checksun sprintf changing */ = TEI4PERATURE + IIUI{IDITY + BATTERY; += $IIND DIRECTION + winal_speed; += rain state; (packet, . u u u $ * 0 3 x- 3 0 1 x .a 0 3 x ,$ 0 3 x . 8 0 4 x g. u . g 0 4 x * Q Q Q , ' TEI{PERÄTURE, I I I ' M I D I T Y , B A T T E R Y , W I N D _ D I R E C T I O N , w i n sdp e e d , { int) rain_state, checksN) , / * N o l e : d o l s w e r e a a l a l e dt o n a k e s s c a n f + / */ /* vork on indoor unit.. #asm{ sei") /i reenable inrerruprs /r packeE aod conlinue to altow sendins to qather data,- the */ */ +asm{"wdr") */ T X _ P O W E R= 0 i /* turn on transnitter delay_ns(20); /* al1ov 20ns for poser up.. */ while (TX_CTS == 0) */ /* sait until tsraDsnitsler is ready.. t + asn ( 'walr' ) t / purs(packet), /, send pdclc. oul while (Tx Counler) I /' wait unLil data is all gone */ *asn( vdr. ) ) delay_ns {20) ; */ /* hold carrier for 20ns afrer end of tx.. RF Tx_Tine = 0; /r reseE Ehe flaq unrit nexr rine */ */ T x P o W E R= 1 i /* power do@ unEil nex! lime.. t o.t.hc' ('x ); / d u m m yt u n . c i o n to alininälF ) Figure 5-2f Ptoposednok1,fot trc outdoot Unit (Continued) dälnirgs.. 3tl 3r2 5,6.I I SYSTEMINTEGRATIONAND SOFTWARE DEVELOPMENTPHASE, INDOOR UNIT The indoor unit software sharessome common features with the outdoor unit in that the ADCs are used to measurehumidity, temperature, baromeftic pressure,and battery health. In fact, the sameauto-scanning arrd name alias structure is used to provide referencesto the software for later computations. There are some key dift'erences,particularly feature-driven differences, in the indoor unit that we will focus on in this software design and int€ration description. In the indoor unit, there are additional routines for keeping time,lighting an LED, and ac cepting the incoming data from the outdoor unit. Most ofthe software in the indoor unit ; dedicated to formulating and maintaining a display. This is common in systemsthat deäl with humans. Humans are a bit "high maintenance" when it comes to de\€loping software to relate to them. The medrods ofhuman communication that we have allowed ourselvesm this weather monitorure the LCD, a couple of LEDs, some bunons, and a beeper KeepingTime Time is kept through the use of the Timer 2 of the Mega16. There are special teatures within the microcontrollet t\at allow a 32.?67 YJlzwatch crtstal to be used to drive an lnternal oscillator by connecting it to PINC.6 and PINC-7. Tirner 2 is initialized to have a prescaleofTlOSC/128. This allows Timer 2 to count up at 256 Hz An interrupt is gener ated at rollor'.er,or once everv second. // clock soulce: Toscl pin // clock vatue: TccR2=0x05; ASSR=0x04; P C K 2/ 1 2 I A structure is used to unify the tirne variables as a block. This is a good method of tying a set of variables together referentially. struct TIME_DATE { anE int ninute; inL secondt inL month,. int day; When Timer 2 rolls over, an interupt is generated,and the tirne is updated. Note that there is no year and that the nurnber ofdays for each month is tested against a look-up table to establish when a month is complete. This means that the user will have to manually adjust the date on l€ap year on this weather monitor. Figure 5-22lists the interrupt routine. The real-time nature of this rcutine also provides a method of testrng for communications from the outside unit. Whenever an outside unit telemetry messageis success{Lllydecoded, the variable "outdoor_okay' is set to 15. Each second or pass through the interrupt Proje.tDeqelofme"t struct int TIME_DATE { hoür; int int int b seconat; nonth; day j . inqi ed /" /* seconds without walid +define ouTDooR_TIMEoUT char outdoor okay; /r r imF bei ns edited comunications 15 outatoor unir f lds , */ is */ ta1king.. nax day for a given nonEh r/ /* leruln con6t char flash MAx DAY[13] = { 0,31, 28,31, 30, 31, 30, 11,31, 30, 31,3 0, 31 )' bic loqv l.a- or: in! in! in! in! void rain this hour,. rain this day, lain-lhis month,. year; lain-lhis backup rainfatt(void); /. lou /* collecEed /* batcery tlä9.. rainfall prototl@e '/ atara */ EEPROMbackup 2 owerflow interrupE /* Tiner service routine and happens /* This is used to keep "Rea1 Tine" /* every 1 second inlerrupt tiner2_ovf isr(void) ITIM2 oVF] void if (edilins) /* lime if is being */ so alon E updare itt */ ! (outdöor_okay) /* tine outdoor-Okay if(++tine.second { edited.. loutine alo@ for ; > 59) lime.second = 0; /' count */ */ up seconds /" enou€rhfor a minure? if (++rine.ninuEe > 59) t == 1) if (towv_in_error Figure 5-22 */ valid comümicatiöns unit /* fron outsiale ri,li,et 2, ReoLTne Chck h'temrpt Rouüne(Corfinrres) */ */ 313 3t4 runninqr on 1or battery /* if backup rainfall O ; data every hour.. /* backup rainfalt rain this hour = 0; fo. the hou... /* reset lain tine. ninuEe = 0; */ for an hour? /* enoush ninutes if (++tine. hour > 23) */ I () , backup rainfalr e very day to eepron t a c k u p d a t a "/ /* - 0,' rain Ehis-daY raid for rtle day. /* reset = 0; tine.hour a alay? for /* enoush houis if (++tine. alay > üax_DAY I tine. nonth] ) { = 0; rain Ehis-nonth '/ /* reset rain fo! Ehe nonth.. Eine day = 1; monrh? /t enoush days for this > 12) if l++tlne.nonEh { /* /* lain-rhis Year = 0; resel rain for the year.. E'me.monlh - I; year gone by.. anolher */ t t ) J' Figure s-22 Ao.klnte fi|net z,Reot-T-t.lie "pt Rourine(Gntinued) routine, this rariable is decremented, and as long as the ralue is nonzerc, we know we have reasonablycurent weather data. Also note that the flag "ealitins" is used as a method ofholding off the updates of the time structure during the period that the user is editing th€ time md date. Low-Battery Indication The low battery LED and low-battery conditions are monitored and controlled within a timer intetupt. This a1lowsthe test and the handling ofthe LED to be a time-independent process.This code could be performed in the rzaizl'l routine, but the flashing ofthe LED would then be subject to other processesand €t(eptions, like the display update time or a user pushing the buttons. Figure 5 23 lists the code for handling this task. Projüt Derela4nent +define BATTERY +define +define Low INDooR_v Low ouTDooR_v 306 306 {detine !O l BA11 LED PORTD.6 voro bä^k!p adc_datat2l rajn'alllvoid)r analog /* A/D a/D /* /* /' /' chan counts counts 2, tbat that refale refare low bäl Lery /* */ inr Eo 4.7v to 4.7v ird'.d a u F c Li o n p r o L o t y p e . / sdve rdintdlr !o eep!on o ' Tiner 0 overftos inteftupt serwice routine /* lhis happens about every 4.096ns /* inberlupl rinero owf isr(void) ItIMo OVF] void { /' keep coual for btinky light.. */ < LoW_OUTDOOR_V) if (outdoor battery 1o0v oüt effor = 1; Detect errors and 'tatch' then /* if (BATTERY < LOW INDOOR V) */ tshe eüors are cleared elsewhere /* I = = if(1ow in error 0) () ; backup_raiofal1 backup rain sause alaEa., in case */ /* of power failure. /* . Iowv in error 1, J if (1owv,oul-er!or) LOit BATT LED = 1; d:isplay errors on LED /* /* 1ow outdoor.. on soliat.. */ t if(rrc & 0:40) /* low indoor.. LO''I-BATT_LED = 1; LOW BATT LED = 0; J IO9i_BATT_LED = O; +asn("sdf,") /* pet the dog--- +/ ] Figur€ 5-23 Low-BotEry lndi.otot Hondler,Tmer 0 ISR b1ink.. */ */ 315 3r6 Another adiantage to using a timer intemrpt is that the battery health reading is updated by an interupt routine, and the fact that it is tested within an interupt routine lends protection against using a value drat could change in the middle of the test. Normally, the rn terrupts would need to be turned off duing this gpe of computation, but since no inter rupts are allowcd while one is in process,there is no need for disabling them. The Buttons and the Beeper The buttons are simple switches that are brought in on input pins and monitored directly by the software.The definitions for the buttons look something like this: for buttons r/ /* deftnitions #defiDe #define UNITS BUTToN SELECT BÜTToN #define SET BUTTON PINA.s PINA.6 PINA. ? The beepermanagementis alsokept simpleby utilizing the Timer 1 peripheralin P\4M (? lseu;dtb nadulat;on)mode.This allors us to simply setup rhe timer for the output frequencywe want, and then, by placing a duty ryde into the output compareregister (OCRIAL), we get a tone at a volum€relatedto that duty cycle.The PIAM is initialized like this: /* /* Timer/Counte! Clock source: 1 lnitializarion systen clock 500 kHz /t Clock value: /* Mode: 8 bit Putse width /* OC1A output: Non Inw, TCCRlA=0x61; TCCRlB=0x03; üoalulaEion Then to control the beeper,a couple ofmacro functions are used: #define BEEPoNO {TccRlA=0x81;TccRlB=oxoa;ocR1ar,=ox4o;} * d e f i n e B E E Po F F O { T c c R l A = o x o 0 ; T c c R l B = 0 x 0 0 ; o c R l a L - o x o o ; } This is done to make the code a little easier to reäd. The teat "BEEP oN ( ) ; " is replaced with the tex:t " {TccRlA=ox81; TccRlB=oxoA; ocRlAt-=ox4o; } " during compilation. Figure 5 24 lists the button/beeper handler routne. void check_but!ons (void) I if(UNITS BUTToN) i f (1asr { Fisure s-24 units /* toggle units: hperial == 0) units ^= 1; / * t o q r q r l eu n i r s , . Exon4e ButtonlBeeper Handter(6ntinues) */ < > l4etric */ ProjertDeae/a?nent lasl units = 1; B E E P , O N O; delay_ns (25 ) ; /* renenbe! = 0; /* finser that button is */ down., ] J last units off of tütton? ]/ perioal: Il, D, M, Y if(SELECT BUTToN) /* Lossle raiDfall { if (last_selecl == 0) t which_rojnr r; pe' od., /' toggle,äinrdll r/ which_rain &= 3; /* 0-3 te11s which perioil.. = 1; last_select /* renehber that button is down.. BEEP_ON{ ) t delay frs (25) ; I ) last_select = 0; /* fin€rer off of button? i/ r/ if{SET_BUTTON) /* set tine anal date?? t if (lorv_out_error ll lowv,in error) t lowv out er.or = 0; /* clear LED errols and rerurn lowv in error = 0; B E E P , O N (} ; delay_ns{25); ) == 0) /i othesise, if{last-set t s e L _ L i m e _ d aL e o , last set = 1, /i renenler B E E P O N ( ); delay ns (25) ; ) edit tine */ that butlon is ] läsl_se( - O; /\ finger B E E PO F F { ) ; ) Figure 5-24 Elf,'lpb BüanlBeeper Handlet (CütiNed) ol i ol */ buLLoa? '' dosn,, */ */ 3t7 3t8 While nany q.stems rely only on a tactile, or "clicky," bunon to provide feedback to the user, the beeper impror.es the "fed" of the rystem. The beeper provides a confrmation from the software that the button press was acknowledged- In the future, the tunctionality of the beeperin this weather monitor could easily be o<pandedto provide audible weather alarms, or even an alarm dock feature, sirnply by software embellishment. Decoding the RFTdemetry The telemetry from the outside unit is handled very similarly to the way it was constructed for the outdoor unit. The REDET input is used as a pting signal to indicate that an RF signal is on frequency, that there is a good possibility it is from the outside unit, and that there may be data aswell- The INT1 interupt is conligued for rising-edge. This causesan interupt when the RF is f,rst detected. The INT1 interupt routine sirnply enables the USART receiver and intemrpt: r arn,nt ' 'lhis r cprvice routine on RF recepLion.. [EXT_INT1] voial exE_int1_isr {void) occuts interrup! { Rx_Wr_Index = iJDR; Dy_lrrr_Tndex - 0; = Ot Rx_Rd_Index Rx_CounEer = 0; Rx_Buffer_Ove.flow // clear //reseL chars any index ol .exr fron input cl-d' i.alex of next char / /reseE rhe Eotal count of //reseE = Ot // . -aad any errors of -o b- USART p. !o be fetched characters I This methodofgating reducesthc parsingofspuriousnois€asdata.The receivefunction of the USART is handledby intemrpt much in the way the üansmit function ofthe outdoor unit is handled.This automatesthe recq)tion and buffering ofcharactersand ,llows us to utilize the standardI/O finctlons getehar) and seanfl)to patsethe lnformatior packets fiom the outdoorunit. Figure 5-25 showsthe codefor the intenupt serviceroutine. interrupt /* UART Receiver interrupt IUSART_RXC] void rouEine service (voiar) uarr_rx_isr { char c = 0; Rx_Buffe! IRx,lt!-IDalexl - c_ /' put received > RX_BUFFER_SIZE) /t if (++Rx_Wr_Index = 0; RX i'ir Index Figure 5-25 rntefflJptorvenUSqRIRecete(Contnües) wrap char the in pointer buffer */ */ PrajettDe"ela?nent 319 */ > Rx BUFFER srzE) if(++Rx counter count /* keep a character * * / ovelflow check.. / \ - R X _ B L T F F B RS I z E i Ri.'Couj te! if too nany chdls cane ' /' = 1; Rx-Buffer_ove.f1ow lhey could be used */ /r in before r/ could cause ao er!o!!! \ /r lbat ) /' Get a characte! char setchar (void) fron the OART Receiver */ buffer { char c = 0; while(Rx Counter == 0) if (i++ > 2000) reEuln 1; c if Dx_Bur-er'Rx_Rd_Tnderl; - if /* / qet (++Rx_Rd_Index > RX_BUFFER_SIZE) = 0, RX_Rd_Index if (RX_Coun!er) --: Px_-o.nre /' nov, we include */ replacenenrs +include the library wair ore /* wrap functions anal it wilt for tron keep d counL of qetcharO with ours.. /* version the other stdio.h /* That way, all +define _ALTERNATE_GETCHAR_ /* /* enpry, a character... */ Lhe bLtfe,..' the (buff- can */ pointer s use unalerstanal z.) then! our ! r/ */ <srdio. h> Figure 5-25 (Co'Ittn',ed) lnterrupt-DrtenUSARrReceive The main loop, in tuncoot na;n), wztcJrest\e rariable "Rx-counter", which indicates the oumber of characters in the receivebuffer. While there are charactersin the buffer, the tunctron gxchar) rs called and the rctumed characters are checked for a start ofmessage. As defined in the outdoor unit software, the format ofa t€lemeüy packet is as follows: . -L$!Lc.hhh.wv.ddd.ssss. r.xxxx'OO0 320 where at is the temperatue ADC rea?t;lrg,tht is the humidity ADC reading, zzo is the battery voltage reading at the ADC, and l/1 is the wind dnection. The data for the ADC readings are each sent as 3-nibble values, becausethe ADC vatues will be between tu000 and OxFFF.This savestrarsmission time by reducing the total number of characters sent. The value s.r.ris the wind speed (Timer 1) reading, r is the rain gauge state, and x,*r is a checksum made up of the sum ofthe data itself The values are all in hexadecimal. The do ar sign ($) is used to indicate the beginning ofa data packet, and the asterisk (-) is used to signal the end of paclet. The L/r-r{/and QQQ are preamble and postscript data that are used to stabilize the messagefor RF trarsmission and are to be ignored by the receiver ( ) " is called to Once the start of message($) is detected, the mutine "set-outdoor-info (refer retrieve änd decode the data to Figure 5-26) . A tenporary buffer called "packet" is loaded with aI the data between the $ arrd the * markers Once the * is received,the USART receiver is disabled to prevent bogus input until the next transmission fiom the outdoor umt begins. The stardard libtary fincion scarf) is tlten used to parse out the values and place them into the aDproDriateräriables. +deflne chai int int outdoor okay; /* 15 /* outdoor seconals withouL unit p-.\^r get_outdöor void /, [18-: burf-. ror valid comunications in.oming */ variables o-.doo. daLä , / / * u n u s 2 7 6 , 8 0 0 . 2 E 8 . 2 F F . 0 0 3 2 . 0 . 1 0 9 5 * Q Q*Q info (void) char *p = 0; char c = 0; inr chk = 0; whiLe(c l= '*') /' qdLhcr /* Eoo ddld Ja il -rd I if (++chk > 46) Figure 5-26 */ ralking. . */ is r d i r , o u t h , r a i n , c h e c k s u n ; / * renporary lasl rain, rainfall,which rain; . 1_ . { ouTDooR TrMEouT nuch qarbaqe? Telenety PoßingExonple(Cottinues) '/ o F-ssaSF. Praja/ Depe/a?nent break; ) c = seLchar o ; == -t) if(c /* not r/ enousrh characters? break; J 'p /' 0j UCSRB=oXo8; if(c == -1) /' disable /* packet nul1 terminäte leceive. was junk-- lha until L sL.irS.. Dexr Eoss it.. line. - */ r/ */ into va.iables /* parse out the parameters c = (cha!) sscanf (packet.' gx- gx. gx. gx- *x. *u. gx', &out_t, &ou! h,&out batE,&w dir.&s speed, &rain, &cbecksun) ; */ paraneLeis.. the coun! of assiqned /* c now conrains chk chk /* = out t + out h + out_batt += w speed + rain; lest the if((chk + w_dir; nunber of pareelers ad the == checksun) && (c == ?)) OL(doo' .Okay conve.!_ou!doo checksü for a va1ld nessage O U T D O O RT - I M E O U T ; / ' l e s e t c o m L : m e o . /' update ddfa to! oisp.ar, _daLcr); r/ .. ] ) Figure 5-26 TelemetiyPoßineEompte(co inu.d) Once rsra4flJ has pulled the values from the text strean in the buffer "packet", the values are added together and tested against the value "checksum' to make sure that the data is free ftom conuption. (This method of srmming the data mimics that found in the outdoor unit software.) Ifthe data is complete and intact, the \,äiable "outdoor,okay'is set to the timeout value of 15 seconds,resetting the "no outdoor data" condition. The data is pulled into temporary va;iables becauseit all must be scaled into real units at a later point. Collecting and Protecting Rainfall Dat4 Rainfall is collected as transitions of a tipping bu&et or seesawover time. In our weather monitor, we are using the RG T rain guge. Each transition ofthe tipping bucket within the rain gauge is 0.01 inches ofrainfall. The valu€s "rain" and "fast-rain'are flags used to determine when a tansitioo has occurred at the rain guge, and the data is allowed to be collected ooly at the transition. Variables are set up to accumulate hourly, daily, monthly, and yearly.Each time the gaugetransitions,0-01 inches is added to all ofthe accumulations. 321 3n The real time dock ISR (Tirner 2) resetsthe accumulations at the beginning of each hour, day, month, and year, respectively,as those times change. The math for rainfall, as in all ofour measurements,is handled using fixed point numbers. This means that basic integer arithmetic is performed and the decimal point is "mental$' lixed in one place. Floatingloint math is available in the CodevisionÄVR compiler aswell as in others, but in general floatingpoint suppon is big and slow and is not usually necessary for doing simple unit conversions.Using rainfall as an example, each time the gauge state chang€s,0.01 inch€s is added, but as you can seein the example code in Figure 5-27, eachvalue is increment€d by one. This saysthat our decimal point is to the right ofthe 100s place,which means that one inch ("1-00") of rain is rcpresentedb1' the integer number 100. For us to display the rainfall in one-tenth inch units, we simply divide the accumulatedvalue by 10 before displaying it. The rainfall information comes in rery dowly A power outage with a low banery condition woüld causethe loss ofdata that could have been collected for as much as a vearl We couru simpty havedeclaredthe mriables used for rabfall to be located in EEPROM, but the potential ofwearing out the EEPROM from arcessivewrites also exists.In this weather monitor iaE lasl rain, rain, int rain this hour; int rain Ehis day; int rain_Ehis nonth; int rain_this_year; void I qer if(rain iainfall vhlch_rain; (void) l= tast rain)/t rain this hour++; rain rhis day++; rain-lhis month++; rain_this_year++; )dh buckeL (seesaw) has /* Each tip of Ehe b,ucker = 0.01 ' /* These values are all inteqers as if Ehe value is a /* are treated /* with the decimal at Ehe 100s .F_ro /' r ) .onvarr satF.tad */ transitioned vdtLc -ö. */ of rain' / and */ fraction '/ ptd!e. d sp .y { rain_Ehis rain Fisure 5-27 Ehis hour/1o; /' /* /* se s o w e scale doen. monLh/10; RoinfalCo edionExon'pte(Contjnues) the number a/ Plojeet DetetaPnent .dinrd-l räin this 323 yea!/I0. poiEE, 1/10ths of a incb decinal /* dewelop fixed = rainfall raln_nantissa /' ^öw the value is / lot * 10); = raiofall (rain-nantissa rain_frac = !ai!; Last rain */ "mant. frac' */ (Continued) Fisure 5-27 RoinfolColedionEj,€lllple example,we "frIe"the rain datato EEPROM in orderto protectit. This is donein a couple ofways,daily and intelligendy. The daily methodis shou.nin the rsl time ISR (Timer 2). Basically,all the accumrilations are savedto EEPROM at the end of eachda)aThe intelligencecomesin the form of a "smartsave.'At the momenta low-batterycondition is detected(or withio 4 milhseconds ofit), the current accumulationsare savedaway.Ifthe unit is running on batt€ry and this low-battely condition continuesto exist,the real-time ISR will sar.ethe data everyhour, until the systemquits from lossofpo*.er. This f,1ingof the datagreadyreducesthe activity on the EEPROM, making it last longer. though.When the sJstemis povreredup from a There area coupleof other considerations, lrom mustbe pu11ed failedbattery conditionor for the firct tirne, the rah{äll accumulations the 61ebeforewe continueto add to them.The other consideratioois the validity of that data.Here is an exampleof how it is han<lledin our weathermonitor: if(raqbyte != 0x55) I eeproa uninitializeal. /* if / * clear it out before using then 1e,, i/ */ () ; backup-ralnfa1l = 0x55; tasbyte \ !ain_this_hour laiE_lhis_dat !ain_this_nonth rain_Ehisl.ear /* qet hou!,save; values fron eepron., i/ = rain = rain day save; = rain nonlh,sawe; = rain year,save; The ralue "tagbyte" is setinto EEPROM ir orderto determinethat the EEPROM is in a known state.When the monitor is poweredfor the fust time, the EEPROM default,or erasedvalue,is 0xFF.Thercfore,"tagbyte" will readOxFF.We cornparethis valueagainst a knolvn like 0x55.If it is not equalto this knovm, the EEPROM is initialized and the "taglyce" is setto 0x55. 324 CONVERTING FROM COUNTSTO REAL UNITS As stated in "Operational Specif,cation" in Section 5-6-2,"Defnition Phase,"the data for all ofthe weather panmeten are collected in the base measurement units, such as ADC and timer counts. This keepst]rc acturl collecnon processclean and simple. But here we are back at the human interface again- The problem is that most people cannot mentally convert from ADC counts to temperature in "F. In facq most people have a tough enough time 'F 'C. going fiom to So as develop€$, it is oul task to do this fancy thinking and present the information to the human in a nice prepackagedform. Figure 5-28 shows the code used to convert the inside temperature, humidity, and baro metric pressure.Just as in the rrhfrll measurements,füed-point arithmetic is used. Most unit conversionsinvoh.e two parrc, a slope (or gain) and an oIFset.lt dependson the gpe of conversion to de6ne which part is applied when. +dEfiNE IMPERIAL +define METRTC O 1 // curte t K it = 12, scale /* l* 0-12) const int fLash I offset it = 1?1; */ lemperature, hperial const inL flash alisplay units I indoor tenperature, offset /* l-.a4v) lmperial for indoor */ constintsftashKb=26; /, const int consr 'ons lnl int int int - fLash flash fl"sh prF-sure scete tor böromer ric {r/26) = 280; Offset_b _or /. (28.0'Hq)ofrser p ess. bd o-er'ic K ih = 10, offsal in indoor teftp; balon nantissa, indoor_hunidity; void baron convert,indoor-daEa 0; /' // (1/10) offsel scate, indoor hunidit) ' adoo 'u- d , , frac; {void) I int bar = 0; 'aLF'rup-s lo prcvanl ddld d.sdbllhF .äl.uld, vhilar- parforn:n9 "e + a s m( c 1 i ) ' ' indoor_temp Figure 5-28 = ( { T E M P E R A T U R EI _ O f f s e E _ i t Unit Conveßion E onple (Cotlinues) e lrom.'"-9inS { ? ions ) tI_K_it ) / 100 ; */ Ptujed Deae/o?nekt indoor_tsp = ((indoor_tdp 32)+5)/9t bar = BARoMETER / K b + offset_b; - bat / 7Oi baron mantissa = bar - (taron baron frac nantissa indoor hunidity = HUMTDTTY / /, scale to desrees C */ * 10); K oh + offser oh; +asn('sei") l Figur€ s-28 Unit Convetsion Exompte(Cofünued) In the caseof temperatu.e, there is a voltage offset of0.84 V (171 counts ofthe ADC) that should be removed before scaling the number. Once the offset is rcmoved, the temperature in "F is computed by multiplying the counts by 0.24. The arample shows 6xed point adth metic performed by multiplying the ADC counts by 24, which would make the ralue have 'F two plrces after the decimal (that is, 61.44"F), and then scaling the value back into whole by dividing by 100. Once the tempernture is conv€ned to "f; it is simple to re convert it to metric ifneed be. The barometric pressure and humidity are different in that the scaling occurs before the offset. This is becausethe ralues ofthe ADC go rail-to rail (0 to 5 V DC) and the offset applies to the units direcdy instead ofthe counts. For example,with baromeüic pressure,the ADC value will be 0 V when the pressureis 28.0 inHg. The ADC value is divided by a constant (r<-r) to get the proper number of fractional inches of mercury The result is then offset by 280 (or 28.0 inHg) to anive at the proper value rcpresentation, a number between 28.0 and 32.0 inHg. The same processesdescribed hold tme for the temperature, humidity, and wind speed measurementsdelivered by the outdoor unit. Wind chill and dew point are üeated differendy in that they are products ofa look-up-table. In Figue 5-29, you can se€how temperature, humidity, and wind speed are conened and then those converted ralues are used as indices into a table to return wind chill or dew point in "F. Just asbefore, if the system is orsplaying metric values, the conrrted units are rescaledto metric. Routines for Controlling the LCD Figure 5-30 shows the routines for controlling the 4X20 LCD. The display is an Optrercompätible device operating in ,tbit rnode. This means that all of the data going to the device is transferred using four data lines. This method ofinterface savesprecious I/O pms on the microcontroller but still allows the display to be updated quickly There are three control signals E, RD (or R rW), and RS. E is used as a strobe to validate the data (DB4 7) to the display. RD is used to indicate that the operation is to ftad data ftom the display 325 326 +define TMPERIAL +define METRTC char units; 0 1/* current display r/ units int in! in! in! outdoor tenp, wind chi11; wind speed, winal degrees; ouEdoor humidity, dew poinr; ouEdoor battery,. " bit Ä_d'r.oLl_L,r-in,c\ecksun; /' tempordry vdlido-es ' r/ dp va1id, wc va1id, /1 values are valid flaq.. ' Dew Poinr Look-Up-Taole - r m p e ,i d l . / const char flash DEwLUT[13] [11] = { 6, 4, !3, 20, 24, 36, 44, 52, 6t, 69, 77, 2, A, 16, 23, 3!, 40, 4A, 51, 69, 14, A3, 1, 11, 18, 26, 35, 43, 52, 6I, 69, 74, 47, 4, 13,21,29, 13, A2,9!, 11,41,56,64, 6, 1-5, 23, 31, 40, 50, 59, 67, 11,86,94, 9, l1 , 25, 34, 43, 53, 61, 70, 80, 89, 98, !7, 19, 27, 36, 45, 55, 64, 73, 43, 95, 101, !2, 20, 29, 34, 41, 5t, 66, 76, 45, 93, 103, t3, 22, 31, 40, 50, 60, 68, 78, 84, 96, 105, 'L5, 24, 33, 42, 52, 62. 71. 80, 91. 100, 104, 16, 25, 34, 44, 54. 63. 73, A2,93,702, 11A, 11, 26, 36, 45, 55, 65. 75, A4,95, tO4, 113, 74, 24, 31, 47, 51, 61, 11, A1, 97, !O7. !!7 )r t/ - Inperial /* l.Jind chi11 Look-up-Tab1e const cha! flash wc LUTIg] [8] = { 36,34, 32. 30, 29, 24, 24, 27, 25,21, 19, 11, 16, 15, 1-4, 13, -1, 13, 9, 6, 4, 3, I, O, r, 4, 7, 9, tt, 12, 14, -I5, ,lI, 16, 19, 22, 24, 26, 21, 29. -22, -24, -32, 15, 4a, 43, 11, 39, -34, -4L, -45, -44, ,51, 53, 55, 51, -46, --53, -58, -61-, -64, 67, 69, 71, ..51, -66, -7L, -74, -74, 80, 82, 84 cons! int ' /r consr consr int int Fisure 5-29 flash I K ot = 12; (' 0,I2) s.dte oufdoor (-.8.v) flash flash or-scr I I ror LempFrärure, outdoo' K ws = 25; offset ws = 0; (Cornkues) Morc Unit Conveßions mper idl tempercrute, /* /* scale offset ' tnpe!idl */ winil speed, Imperial winil speed, tmperiaL*/ PrajectDe,ela?netut consts in! consE in! -onsl const void . int flash flash K wd = 35; offser wd = 0; /* /* fldsl flash K_oh - 10; = 0; offseE_oh srale, ouLdoor l-u- d /r(l/l0l */ ouraloor hunidiry /* offser. */ (* 0.15) scale winal direclion */ offset winal directiön ! (voiaI) convert_outdoor_datä t intdt=0,db=0,dr-0; long lemp = 0; = outdoor_tenp wind_speed ({ouE_E r = w_speed * offser I_K_vs tenp = (1ong)w_dirt /+ temp *: K vd; lenp /= 100; /* = remp + offset wind_deqrees = ouE_h outdoor_hunidity ouLdooJ_b-lLery - if((outdoor_tenp (outdoor >= 20) huiidity / ot)*r + I use K ot)/100; Offset 1o4g ws; desrees /* MPH /* so we don ! K ih ouL_bdLt; + Offset /. jusE ih; /* .ounts i/ */ '/ <= 90)) t = 1; dp-valid ) el se t de$-point = 0, dp valid = 0; ] /* iEEerpolaEion scale could */ ! g RE <= 120) && && {oltdloor_tenp >= 30) && (outdoo._hunidlty dt = (ourdoor,Eenp 20) / Lor /* dh= (outdoor,humidi ty - 30) /s; index */ be added herel ! ! */ for */ */ overflowl after this, int is safe-. sal; /* degrees fron North F table if ( (outdoo!-Eemp >= 40) && {outaloor tenp <= 40) && (wind speed >= 5) && (rind speed <= 40)) { dt = (outdoor_tenp 40) / 70t /* scale for Lable index */ dw = (wind_speed 5\ / 5i = l . t C _ t U Tl d l I t a t q l ; vind_chi1l wc valid = 1,. coulal be added here Eoo! I I */ /* interpotation ] eLse t = 0; vinil_chill Figure 5-29 Mote Unit Conveßions(O)ntinues) 327 328 = 1; wc_välid ) == UETRIC) (units if - 32)+5)/9; = ((wind chill wind chitl /j scale to desre€s C - 32)+51/9) = ( {dewjoint dev-poinE /+ scä1e to desrees c ouEdoor lemp = { (outdoor tenp - 321*5)/9. ro degrees c /* scale = ((wind_speed)1881/55; vind_speed !o KPH /* scale ] ) Figure 5-29 +define +define +define +define (Coninued) Morc Unit Conveßiorß LCD_E LcD_Rs LcD R9l LcD PoRT pORTB.o /" LcD cont.ol PORTB.l PORTB.2 PoRTc /t LCD DATA pORT (loresE Lines */ 4 b:irs)i/ */ positions lhis Look up lable cranslates LcD line/cursor /i */ inro lhe displays internal nenory addresses /i const unsiqned char flash addLUT[4] = {0x80,0xc0,0x94,0xD41; void I sr half(unsigned LCD Rld = 0; LCD_E = 1; LCD_PORT = LCD_E = 0; char /* {data data) set */ E /* raise p u L & 0x0F); data /* /* drop E LcD Rl,i = 1; /* disable de-ay /r dllow msr ), t/ irR actiwe liR disprdy on port */ */ time Lo lhink J vo:id wr disp(unsiqned LCD_RW = 0; LCDE=1; r,cD PoRT= (dara LCD E = 0; Figure 5-30 char alata) /* enable write., >> 4); /* strot'e upper LCDCo'nrctRoutines(contitues) */ half of daEa a/ */ */ */ 3n Projeü De!.lofn. LcD E = 1; LCD,PORT = LCD-E = 0, {dara */ /* out Eo the alisplay & 0x0F); the loter half /* now. strobe LCD-Rit = 1; /* disabte delay /* atlo{ ns(3); write tiRe for r/ */ LCD to react */ J void I init_display{void) ehar i = 0; L C D - R W= 1 ; LCD_E = 0; ircD-Rs = 0; delay_ns(s0); /* /* preset interface signals-. comand node-- */ d- ha-t{0x13); wr half(0x33), w! halt(0x33); w!-ha1f(0x22); / /* /* /* This sequence enables the displä} rot 4-biL inlerface node */ these comands can be founal */ data sheets in the nanufaclurei's */ 5xl font' +/ vr-disp(0x28); /* EDable the lnternal wr_disp(0x01); */ sr_disp(oxlo); cursor to mowe {instead of alisplay shif!) /'6et sr_disp(0x06); */ the displav and not shift /* ser rhe cursor to nowe riqhl, v! disp(0x0c), */ off änd cursor t'linkins off, /* turns display for(i=0x40; i<0x5F; i++) { delay ms(10); LCD RS = 0; {! disp(i); delay_ns (10) ; disp-char{0); ICD-RS = 1; /i /* init data node characEer font ran to "00' */ J void { line (char which-1ine) tCD RS = 0; ; trcD_aDDR = addruT Ishlch_1ine-11 wr_disp(LcD ADDR); /* nove to wtlich-1ine tCD RS = 1; Figure 5J0 LA Contnt Ro/'nnes(Conünues) line */ '/ 330 LCD_ADDR = 0; votd cLear display(void) 'JCD-RS = 0; w. disp(0x01); delay_ns{10); LCD_RS = 1; line(1); clear /* display a.d hone */ cursor J ro id set_I CD_cur (char .har LCDlow, LcDcol ) { LCD_RS = 0; LCD ADDR = addLUT[LCDTow] vr-di sp ( LCD-ADDR ) ; + LCDcol; nowe /t Eo row and */ column LCD RS = 1; LCD LINE = LCDlow; ) wöid disp_char (unsisneal char c) t LCD RS = 1, wr disp (c) ; LCD ADDR++; if (LCD-ADDR == 20) line(2); if (LCD_aDDR == 40) line(3); if (rcD_aDDR == 60) line(4); if {LcD ADDR == 80) tine(1); void { disp_sir(unsiqroed /* auto@ticatly ctlar 'sa) char flasb /* srap display text as srring +/ required fion RAM */ while ( *sa != 0) disp cha.(*sa++); ) void t disp_cstr (unsiqned while { *sa l= 0) disp char(*sa++); I Figure 5-30 (Codinued) LCDCo'tttolRounnes *sa) /* disptay strinq f.on RoM */ Praje.t D.seta?nent (RD=1) or write data to the display (RD=O). The RS signal is used to indicate to the display that the data being transfeffed is a command (RS=O)affecting the displayt mode of operation or data (RS=1) that is to be displal,ed. The function "init display ( ) " configures the LCD for the appropriate operation for the weather monitor. The internal character set is used. the cursor is turned off. and the graphic charactersare deared. The manufactuer's datasheeton the LCD display describes each ofthe command and register seftings for the display, aswell as any time requirements. Some of the commands take a while for the display to execute,so delays wete inserted between these commands to gir"e the display time to complete the operations before the next command is issued.The functions "wr-ha1f { ) " and "wr. disp ( ) " are used to send only the lower halfof a blte or both halves, respatively. The remaining commands perform the text display operations that will make it easyfor for matting and displaying the weather information. The "set LcD-cur ( ) " function sets the invisible cursor to a specified row and column. The "line ( ) " tunctron setsthe invisible cursor to the beginning of the specifiedline. The "clear display ( ) " tunction wipes the display completely clean and sets the invisible cursor to the upper left corner (row=0, column=0). 'disp char ( ) " is th€ l utchar1 for t\e LCD-Its funaion is to place a character on the dßplay The invisible cursor is automaticälly moved, within the display, to the next position. Some tests have to be performed to check for the end ofthe display 1ine.The cursor does not nutomatically " wrap" to the ne'rt line; therefore, the cursor addressis checked,and, based on the addresssize, the appropriate "line ( ) " function call is made. The "disp_str ( ) and "disp_cstr ( ) " functionscall "disp_char ( ) " in order to place formatted "C" strings to the displal "disp_str { ) " is used to display strings located in ( ) " is used to display strings located in FLASH. SRAM and "aisp-cstr Keeping the Display Up to Date The display is maintained as a low-level task. This n,ens th^t nain) eirhcr worla on the display or calls display related functions when therc is time to do so.The display items are common in form, so a simple way ofupdating the display is to treat each item ofthe display in the sameway A structure is used to indicate all the properties ofa display item. slruct DISP_ITEM { row; char flash char flash col t char fLash *fntstr, *vaLue; int *units char flash iunits char flash cha! ftash soulce; I; M; */ /* röw position /* /* /* /' /t */ sprintf fo.nar pointer co variable eo disptay */ */ unics nark imperial uniEs nark neEric */ i4side or ouEsiale neasurenent */ of texL 331 332 Each display item has a position, "row" and "cot", a format, a value, a units indicator, and an indication as to whether the data came from the indoor unit or the outdoor unit- By creating an ,iray of these items we can almost completely describe the display contents: st!uc! DISP 0,0, I1'EM nain alisplay IS3d', &indoor = lMAx-ITEr,rl temp,"F ','C ,INSIDE, 0, ?, og3d',&outdöor_temp,'F',"C ", OUTSIDE, ', C ",OUTSIDE, 0,14, !ic*2d', &winal chi1l,'F 1,0, 8S02u" , &baron nantissa,'.",". ,INSIDE, 1,4, "t1u ,&b.a!on frac, ", ",INSIDE, 1, t, *3u" , &wind speed, "üPH" , 'KpE" , OUTSIDE, 1, 14, " $03u", &wind alegrees, . " , ouTsrDE, 2, 0, " I$3u", &indoor hunidity, " "*", '9",INSIDE, 2, 7, "O*3u, &outdoor hufridity,'t ", " g", OUTSIDE, 'F. , 'c' , OUTSIDE, 2, 14, "DPS3d", &dekjoint, 3,0,"302u,&rain nantissa,'.','.',oUTSIDE, 3,3,'B1u,FiraiE frac, "\" ", '\i r,oUTSIDE, 3,?,'902u.,&Eine.hour, " :, :",rNsrDE, 3, 10,'*02u",&Eine.ninule, " ", "', rNsrDE, 3, 15, "902u",&Eine.nonrh, "/", "/', rNsrDE, 3, 18,'t02u",&Eine.day, " ", "', rNsrDE Jt ( ) " formats and displays the In Figure 5-31, the function "update_dispfay_itm requested item. The cursor is placed, the value is formatted into a display string using s?r;nll1, ^nd 1t is p\tt to the display using "disp_s tr ( ) ". lf the vrlues are outdoor measüements,basedon'main displaytiteml -source", and the data has not been refreshed in the last 15 seconds("oubdoor okay"), then the digits are replacedwith question marls. Also note that if wind chill or dew point values ,re out of range, their digits are replaced with dashes.Finally, the appropriateunit tert, "main displaytiteml .units I" or 'main display i ite,nl . units_M", is sentto the displaybasedon which units havebeen requestedby the user, +define rr4PERrAL *define r4ETRrc o 1 cha! cha! units; text bufferl24l; /* current display unils chär Ourdoo! /* outdoor unit talkinq-. /* display +define #define +define Akay i iten rNsrDE OUTSIDE MAx ITEM Figure s-'3 | table descripEion is for the nain 'i 16 Toble.DivenDisW RoutineExonpte(Cofünues) */ '/ display Ptujed Derelo?neht char whlch_lten; struct DISP T1'EM I .har r-asn touj char flash co1; .ha! f-ash 'fntstr; *vaLue; inr cha! char struct flesh flash DISP 'uniL6_vi source; ITEM main display posjtjon / o. texL /'low r/ of lext /* co1 position spr'r, I ro'ndL /' to wariable ro display /* poinrer */ /r /* i/ uniLs inside mä.1 dFrri. o. outside IUAX_ITEM] measuremenE = ',INSIDE, 0,0, I43d , &indoo!_tenp, 'F ','C 0,7, 083d", &ouldoor_tenp, "F ', 'c ',ouTsIDE, 0,14,"WC82d',&wind_chi11,'F','c',ouTsIDE, 1, 0, "B802u", &baron_nantissa,' -','.', INSIDE, 1, 4, "91u", &baron f.ac, ". ", INSIDE, 1, ?, 's3u', &wind speed, "r{PH",'KPli",ooTsIDE, 1, 14, " t03u', &winddearrees, ", ",OUTSIDE, g', rNsrDE, 2, 0, " r$3u, &indoo.-huidity,'3",' 'g', ouTsrDE, 2,7, og3u", &outdoor_hunidity, " * ", 'F', O 2,14, DP83d' , &dewjoint, "C", UTSIDE, ouTslDE, 3, 0, "902u", &raln_nantlssa,'.',',', i\i i, i\i i,oüItsIDE, 3, 3, "g1u',&rain_frac, :',' :',INSIDE. 3, 7, "902u',&tine-hour,' 3, 10,'902u',&tine.ninuLe,' ". ", rNsrDE, 3, 15,'902u', &rime.nonlh,'/", "/", rNsrDE, 3, 18,'902u", &Eime,day, ,',' ",rNsrDE woid upda!e_display_iten(char iten) { set the LcD culsor ro Ehe iten s position /* firsL, set LcD cur(nain displaytilenl .lov,nain displaylitenl r/ .col) t . pla-e -he va!iab]e inLo its proper fo'.dL -s d sl ':19 ' sprinrf (text buf fer, nain display t iEol . fnEsEr, *Gin_alisplay t itenl . value) ; _ if inside datd.. then dlhdys displdy r/ -source != rNsrDE) if (maln-displaytitenl r/ if it is, qreall { /; outside data nay not t'e up to date., if (outdoor okay > 0) */ /* if wind chitl or dew poiD! out of rane'e... | == NIND-CHILL-ITEM) && {wc-vä1id == O)) if(((iEen = = D E W - P O I N T - I T B M )& & i d p v a l i d = = 0 ) ) ) ((iten Figure 5-'3 | TobEDtiven Di9'/f|/ Rdttine E onple (Cotuinues) 333 334 t s = text buffer,. /while(rs) | /\ reptace iflisdiqiE{'s) ) poinE Eo the nunibers fornatted wilh */ text.. dashes.. */ - J j /* otherwise all is we11, just print /* the ouEside info is not current so, .. s = text_buffer; to the fornarred /* point while(*s) /, rcpldce nunbars wi h quesl | (ts) ) if (isdislt { ir-. r/ */ rexr_. ) j / i dlwqys ) disp (text_buffer) sti if (units disp pla.a unirs srrinq ; == II'PERIAL) .scr (nä a displdylitemt.unirs disp_cslr (nain ' lds-.. alisplaylitenl t); .unirs M); J Figure 5-3 | TobleDiven Dßploy Rourjne Exol7lrple(Gntinued) The entire display is up dateÄftonl' nainQ t:y dnply catling the upda re_di sp tay_itan function from a for loop: t/ enEire disptay ilen=o,. which_iten< üax ITEM; updaEe display iten(which i!en),. /* update for(which se!-LCD cur{3,5); /t indicate which (RAIN TYPE Iwhich_rainl disp-cha! ) ; rhich item++) rainfall period seE_LCD-cur{1,1?),. /* indicate wind headins if {outdoor_Okay) disp_cs!r { w r N D H E A D T N GI w i n d _ d e q r e e s / 2 2 ] ) ; disp-cstr(' set LcD cur(3,12); "l; /* - -if /* flash possible.. star vith */ t/ seconds.. */ */ () Ptoje.t Deoeto?me"t if(tine.second & 1) /* to indicaEe lifett */ disp-char('*'); disp-char(''); Additional information, such as rainfall period, wind heading,and a flashing asteriskto indicate seconds,is simply addedon at the end ofthe update.Look-up-tablesaJeusedto provide the appropriatestrings for the display,eliminating the need for giant if-else or switch-casestatementsloadedwith "disp cstr ( ) " calls: const char ftash RAIN TYPE[4] *WIND HEADINGIIT] = {'H','D , M , Y }; = { Editing the Time and Date The editing of time and date are also handled using a table driven method. This allows a simple procedure to deal with all the ralues in the samevray, even with the same code. An editing structure was designed that contains all the necessaryelements, th€ position of the itern on the LCD, the tide or name of the item (teling the user what is being edited), a pointer to the value that carr be changed, and some lirnits to prwent the user from taking the value "out-of-bourds." SIIUCI ); EDIT' I'IEM { cha! flash row; char flash col; char flash title[10]; *value; int inL flash Minvalüe; int flash Maxvalüe; /* low position of text */ /* col pösition of text */ */ /* iren tirle pointer to wariable ro display /* l{ininun value */ /* üaalnun value */ i/ 335 336 struct = { EDIT_ITEü ealiE display14l 0,5, "Month: ", &tine.nonrh,1,12, 1,5, "Day: &time.day,1,31. ", &time.hour,0,23, 2,5, "Ilonr: 3, 5, "üinute:',&tine.ninuLe, 0, 59 The display is clearedand rebuilt to form the €dit sqeen, asshov,n in Figure 5 33 (page 338). A greater than slgn (, is us€d to indicate the cunendy select€d item. The bunons arc processeddiecdy aJIdare üsed to change the selecteditem, selectthe next item to be edited, or exit. The flag'eaitinq" is used to signal the real-time ISR (Timer 2) that editing is in processand the valuesare not to be updated while the user is making changes. Figure 5 33 shows the LCD during an editing process. +define uNrTs BUTToN prNÄ.s +define +dEfiNE PINA.6 PINA. ? SELECf_BUTTON SET_BUTTON SIIUCI EDIT ITEM { char flash row, char flash col; cha! flash ritle[10], iaE *value; int flash Minvalue,. int fläsh Maxvalue; /* /* /t /t /* /* for burrons */ /r defiDirions t/ row positioo of text */ co1 positioo of text */ iEen !ir1e poiDrer ro varialrle to alisplay Mininun Value */ i/ Maxinun value +/ = { slruct EDIT ITEM edit_display[4] ,,rLimc.nonLh,I,12, 0. .. Monrh: 1,5, "Day: ", &tine -day,1,I1, ', &tine -hour,0,2:, 2,5, Hou!: 3, 5, "Minure:',&tine-ninute, 0, 59 Jt /* void set int iten /' /* cleai displayo; /* build iten=0; cur_iten<a; Figu.e sJ2 ealited flaq */ = 0; = li editinq cur_iEen = 0; for(cur beins () tine_date cur tine siqnal inreüupt start sith firsr roütine iren., the entire cur iren++) TobEDtiven E{tjng Exd,npte(Crntint'es) edit tö skip screen.. */ updaEe '/ Praj.t'D.retaPn.nt s e ! l h e I J C Dc u r s o r t o t h e i a e n s p o s t t i o n /+ fitst, .row,edit-displaylcur set_LcD cur(ediE di splay l cur-itenl I 337 */ itenl col); .. pIa-e Ehe v"' idb e inlo its ploper to'odL ds ä strinq g02u',edil-displaylcur ibenl.tirle, sprintf (rext-buffer,'*s 'ed i | _d' sp lay lcur ireml ,value); Äf Ä sEr BLrToA, while(1) { set_LCD_cur(edit disp_char{'>'); /' wäil lor tinqer /* now work each iten-. disptaylcur-iEenl /" dhiLe(SET BUTTON) /* fiaser ota the burlon. +/-, ' and SET to nove . */ -row,edit displayIcur-iEen].co1-1) r/ point to the iten,. off? '/ d e t a y m s( 2 5 ) ; vhile ; ( ( I S E T _ B U T T o N ) & & ( ! T J N I T S - B U T T o I { }& & ( ! S E L E C T B U T T O N)) */ /* wait for a button I'ress.. if (uNrTs BUTToN) /* increnent lbe current iren. . */ /* and do limlE cbecks-- */ I B E E P O N( ) ; time,second = 0; /* reset Ehe seconds to 0 when rine edited */ *edi!-display Icui icen].walue += 1; ilenl .Maxvalue) iteml ,va1ue > ealit-dlsplaylcur if (*edit-dispraytcur *edit-dlsplaylcur i r e n l . v a l u e = e a l it - d i s p t a y I c u r i t e n ] . M i n v a l u e ; */ if(SELECT BUTTON) /* decrenenr Ehe current iten., a n a l a l o l i n i t c h e c k s / * I B E E P O N0 ; time.second = 0; /1 reset the seconals Eo 0 whed tine edited i/ *edit dispLaylcur_itenl = 1; ,value < edit-display I cür itenl Minvalue) ( * e d i t d i s p l a y l c u . i t e n l v a l u e if *ediE-displaylcur ilenl .value - edit-disptay t cür iteml Maxvalue; ) */ /' upilate the iten on lhe screen. .col); c u r i t e n ] . r o r , e d i t d i s p l a y l c u r i t e n l set LcD cu! { edi ldisplay I sprintf(rext-buffer, "gs 902ü',edit display l cur-itenl .title, 'ed'!_displäylcur i teml .vd]ue); Figure 5-32 Tohli$D|,jvenEdiüry E o,rl,ple(Continues) ; 338 disp str (text_buffer) d-_ey_ s'25)i B E E P _ O F F( ) ; whiLe if ( (UNITS ; d /" BUTToN) lirtre Lime lor swir.r se.rlinq.. (SELECT-BUTTON) ) | | (SET BUTTON) BEEP ONO ; delay ms(25); BEEP.OFF () ; set_LCD cur(edit disp_char(' cur iten++; if (cur iren /' a 1ith1e tine for swiEch serrling. displayIcur iten] -row, ealit disptäylcur irenl .cot-1); ); /* erase Ehe current cursor... - */ > 3) ) vhile clea! l (SET_BÜTTON) display0; Figur€ 5-32 /* finttet /t back Lo business o N T D Y H o U R M I U N 2 H 2 5 5 T E 0 3 a) o \_-/ SET Figure 5-33 */ as usuat,, TobleDüvenUinng Exontple(Contjnued) M o */ off? TimelDokUitwindow RX UNITS/+ SELECT/ */ Ptajett Dete/aP"]ent The function "set rime dare { ) " is caled ftom the "check-buttons ( ) " procedure, which is slled lrom zaralJ. As mentioned previously,the display maintenance and user in terlace re all happcning at the lowest level. The normal operation of device is not disturbed by the time spent converting and displaying information, but during editing, the real time clock does not update and other data collection processes?re ignored until the user exits the editing process. 5.6.I2 SYSTEMTEST PHASE At this point in the project, the tests specifiedfor systemtest during the Test Definition Phase of the project are carried out to give the user confidence that the unit performs as deAnedby the specificätions.As stated earlicr, thc tests may be asetensive as neededto convince a cus tomer, or they may be as simple as comparing the results to the local weäther station. For thc purposesofthis targ extensivetesting is aboveand be1'ondthe scopcofthe requirements and would contribute litde to expanding your knowledge ofproject development However, one important topic to be addressedhcrc is what to do if the project does not meet specifcations, that is, it fails a systcm tcst. Problerns such asincorrect calibration ofthe temperature results, lack of lineariry in the humidistat, and mismeasurement of the ra.n gaugewill all be spotted during q.stem test. The important issueis what to do about it, and there are really only two choices:fx it, or change the specification. Changing the specificrtion is only a very last resort and should zorbe required if thc Definition Phasewas carried out properly. So iring it is the only zaalchorceAs an axnmple, consider the wind speedindicator- Its intended calibration was basedon an empnically derived number from the manufacturer (2.515 }Iertz./mph), znd the design allows for some mriation in the actual results, allowing for lossesdue to ftiction, method of mounting, and so on, so that the wind speedcould be properly calibrated. For example,supposethat when we measuredthe output ofthe anemomcter in a wind tunnel at a local university, we noticed an eror of4%. We just did not get quite as many pulses per second out of the system as we erpected at a wind speedof 100 mph. So when we plot the output frequency (Hz) versus the wind speed (mph), our gaph looks something like "Measured A' showa in Figure 5 34. In this case,even though there is sone error, the result is linear, so a simple adjustment of the scaling would be in order This could be accompJishedby changing the scaling constant in the software from consr int flash r K ws = 25; /* scate wind speed, hperiaL r/ const int flash I K ws = 24; /' scale wind speed, Imperial */ This easyadjustment shows the value ofputting conversion constants and calibration frc tors in as constant rariables stored in FLASH memory You can adjust these easily if neces sary without looking through the program to find where the constants or calibration factors 339 340 - 200 ------- Theoreti@l - M.asßdA -------- Maasu€da !E r50 E 100 Wind Speed in PH. Figure 5-']4 Exoi'r,ph, Measüf:d Anen?o,m..{et Output afe used,and perhepsmissingone or two, ifthey arc usedin muftiple pleces.Examination of th€ programwill showthat theseareinsertedin the programend really do not increase or decrease codesizeby their rxe, so they area no-costconvenience. Ifthe resultwerenonlinear,likethe "MeasuredB" datain Figure 5-34, a more seriousg,'pe of conection might be in order,requiring a complexalgebraicexpressionor perhapsthe sirnplerapproachofusing e look-up-tableand somcinterpolation.The choiceof method, ilr this case,greadydependsor the expcted accuracy, the precisionofthe result,and availablecomputingtime. Overafl a bok-up-table (LUT) is a tough approachto beat no matter how great someoneis with "that äncy math." In real systemslike the one we ate describing,it is not uncornmonat all to cromeacrosssomer€ally strenge-lookingcuffes and bendsin the data that are collected&om a device.As lorg as there is curveto the earth, gravitypulling us do*'n" and the sunrising everydayto causea constantchangein temperature,the datathat is collected;s going ha!'ea shape,and it is probablynot going to be a straightJine. So we can convertthe "MeasuredB" data to mph usiag a LUT and linear-interpolation approach.One ofthe bestpartsofthe LUT epproachis that J,oucanusethe data},ouactually collected.Table5-6 showsmeasurcdfrequencies. Ptujett Deae/a?nent (Hetu) 2.5 (nph) Tabf€ 5-l l0 u.6 20 l0 40 50 60 70 80 90 100 48.3 ö8.7 92.6 11.1.3 132.9 169.2 185.8 201.5 /Veosu.edFregue(ies tonwndTunnelTen If the data is more straight thän it is cuflred or S-shaped,fewer points can be used in the.actual table, and the lineir interPolation can fill in the values in between as they are needed' With ten frequency measurementsliom our virld tunnel testing, arr array is formed to create the LUT= 246 */ const int flash \'Jf.eqsl11l= /* fles x 10 i'e' 24 6 a 6 9 2 . ! a 5 A ' 2 A!51' 1 2 5 , 2 4 6 4, a 3 ,6 A 1 , 9 2 6 , r r 3 1 ,l - 3 2 9 ' 1 5 a 5 The following function shows how the frequency detected b{ the-counter and.placed in,the variable'w öeea" is checked against the valucs of the LUT If the speed is lower than the LUT, it i;bss than one mph and nothing canbe computed lf rhe speedis higher than wind the LU! nothing can be coÄputed either, so an error is displaved using a bogus speedof"888 MPH " Once two values are selectedfrom the table, one above"w-speed arrd one below, the delta ("t l") is calculated for the two table values to determine the slope ofwhat is effectively a short linear segment within the long, cuftrd data. The delta fron the measuredvalte '1" is uscd to compute at what point (in percentagc) "" to thä low.t selectedvalue "p""c.' the measureddata would fall on the short line scgment.The basemPh is fhen comPured ftom the indcx "x", and the ftactionalponion of rhe mph basedon the rario ofthe dcltasn added back to yield the actual mPh. void calc int lonq sind speed(voiat) /* t, b, x; vl, v2, v3; if (w-speed <= lrfreqs[0] ) conpute qloba1 var dind speed */ 341 3A = 0; vind-speed /* too s1öw tö /* /* too high "888' is < 1MPH */ neasure, ] if (v_speed > wfreqstl0l ) { = 88a; vi4d,speed return; > 100MPH r/ tö neasure, an effor nessagel I */ ) for{x=0;x<9;x++) t if (w speed > ldfreqs [x] ) fiad /' | L WfJeqsIx{l], b - Wfreqslxl, b'!eak,. rhere rhe counrs falt */ / * in /' rop dnd botto, v-lues x will be our base M!H/10 /t lhe rab'le ) ) v1 v1 v2 v3 = (lonq)w speed - (tons)t'; /* (note the 'casts ).. i= 100L; /* now calculate the percentase between */ = (long)E (tonq)b; /* the two walues '/ * 10 */ = lvl/!2); of I,IPH diff /* percentaqe ' v1 = (long)x v1 += v3 /t wind_speed = 100L; /* nake x into now add in percentaqe (in!) (w1 / !OL); noo /* i/ UPE * 100 (fractionl) */ of difference seale to whole */ MPH */ Therefore, if'w speea.'w-as measuredin this example at 1200 counts, the values as a result ofthe for loop for the index "x" and the top and bottom values ofthe linear segment, "t" and "u", would be t = r , i f r e q s [ 5 + 1 ]= 1 3 2 9 b = r,rfreqs[5] = 1133 Stepping through the program, the computations would go like this: v 1 = ( 1 o n s ) w - s p e e a l( 1 o n 9 ) L ' ; / * ( n o t e t h e ' c a s t s ' ) - result:v1 = 1200- 1133 = 67 vt'- I00Li /' now.alrulaLe lhp per.cnrdq- result:v1 = 67' 100= 6700 v2 = (1ods)t - (tons)b; /' the Ewo walues */ be.,een */ P r a j P . LD ? u ? t a ? t l , n t = 1329- 1133= 196 result:v2 13 = /* ln1/!2); percentase of * l4PHdiff 10 */ = 34,rvhichis 34%of10mph,or 3.4mph resuliv3 = (6700./196) v1 = (1onq)x r IOOL; /r nake x lnto MPH * 100 (fractionl) */ result:v1 = 5 * 100 = 500,which is fxed point for 50.0mph v1 += v3r /+ now add in percentsase of 'Iifference "/ result:v1 = 500 + 34 = 534,agin, which is 6xedpoint for 53 4 mph Find speed = (inL) (v1 / = wind speed finaLlY: 1aL\ i 534 / to /* now scate = 53 nph 10 vrhole MPH */ As you may recallfrorn the indoor unit specification,only whole mph is displaycdOtherit i" aif6."tt to seethe levelofaccuracythat canbe achievedusinga method ofth;s *| "'ot.umple, we .implv th-rowthe fradional ponlon arvayln thi( :'r\rance r 'rm twe. ln rhi. Jt'. lUf una tl".* i"t.rpolaiion can be applied effectively to lincarize a nonlinear result so ihat the project will meei its specilicationsd* As shown in the example above,the purpose ofthe system test is to ensure,to whatever and are comolered Alter the rcs(q qreencce..ar),Lharrhe 'y"re'n pcrlorm" ro speci-fications for usewirh a h'g\ degreeo'corfip'oj..i is ready ."ä., rh. ;." "di,"r'nent" "...rr,.; results. dencem the 5 . 6 . I 3 C H A N G I N GI T U P The Wind Vanes R-Us Company thinls that our weather station is the best thing to come of along since indoor plumbi"g, .ä no- *" fac. th" task of improving the profit margin the product by linding some Placesto reducc cost. Now thät the weather station product is designed arrd proven stable and reliable, whr are the areasthat costs could be re<tuced?In your career,you may be faced with this quesrion time and time again. There are manv arcasin our weather station project where cost could be reduced. It€; such as the humidity senso! tipping rain bu&et, and anemometer are all pretty e{pensive-but their performance is known and therefore may not be the fust pl"e to starting cutting away at the cost. When we started the development process,u"e chose a processorthat would give us ample jncrease or de room to design and debug thi software but we left ounelves the option to creasememoiy and featuies as rcquired, without involving a large redesign effort Let's look at changing thc CPU as a cost rcduction maneuver. Picking a PaIt for a Better Fit The outdoor unit CPU hasvery little software on board.In fact, with the code as it a stands' only about 11% of the total flash memory is used. Looking at other members ofthe AVR fariilv, we need to select a component with v€ry similar features, but perhaps onc with a There are very few extemal connections, so even a smaler pin-count ,Inull'e. -"-ory "pu." oarnvould be acciptable. 344 The requiredfeatruesthat we rced to include area USARI ADCs, and a timer to count our wind speedpulses.The AIMega4S hasthesefeatures,comei in a 32-pin TQFP package,which is a surface-mountpackage,so no socketis required(andit canbe easilyassembledby a rcbot, savinglabor costsaswell), and hasa 4K memoryspace,so it is more closely matchedto our actualapplicationsize.At the time ofthe *riting ofthis text, anAIMegl6 hasa uait costof about86.00.The AIMega48 costsabout$2.00-That carrbe signiEcant. If the Wind VanesR Us Companysells10Q000units, tlut is a S400,000costsavings(and you will be a hero for making the changefrom anATMegal6 to an AIMega4S!). Changesto the Schematic Figure 5-35 showsthe outdoor unit schematicmodfied to work with the ATMe948. Signalswere simply movedaroundto the appropriatepins, picking up the requiredfunctionality of the USART, ADCs, and timer. Changesto VO Mapping Becausewr thought aheÄ ardused #defneto assignfirnctionalnamesto speciic VO pins, it is easyto look at the softwareand knowwhat few changeshaveto be madeto supportthe designchange.The VO specifc changesareasfollows: +define +define +define +define RAIN_INPUT' IiTIND_SPEED_INPUT TX_CTS Tx_PowER PrND.2 PIND.5 PINB.o PoRTB.l /* /* /* /* qauqe rain anenonerer transnitter rransnirrer input inpur clear power */ */ to send */ */ enable There areother changesthat go witi these,induding the DDRB and DDRD settings,as well asthe defaultstatesofPORTB andPORTD. Thesechane€scanall be madein the initialization fuoction. void iniL_AVRlvoid) /r ciystal Oscillator division facto!: 1 */ *piagna optsizecLKPR:ox8o; /t these iasEructions musr be */ cLKPR=oxoo; /* withiD a few CPU cycles, so optinization disableal */ /r is tenporarity +ifdef _OPTIMIZE_SIzE_ fpiagia /* optslze+ Inpur/output PORfB=0x00,' DDRB=0X02; Ports /* initializario4 enable radio powe. r/ control */ */ Proj?.tDeeeloPtxent 345 o o ! J> 3 o : En o ü v> *, o d 0, ?i 3 t u =t I t & B :6 at = * f, € e e ggüäE ? rrt E .go II 346 DDRC=0x00; DDRD=0x02; e n a b l e U S A R Tt r a n s m i t t e r /* /r Tiner/Counrer 0 iniLialization /* Clock source: Syslen /* walue: /r Clock Mode: /* OCo output 62,50O output */ */ Clock kllz OutpuE Coupare r Disconnected TCCR0B=0x03; TCNT0=0x00; ocR0B-0x00; /* Tine./counter /* ctock ' source: 1 initialization T1 pin Risinq I'lode: Oulpul Co-pdr- /* ocla output: Discon- /* oclB output: Discon- /* Noise cancete.: capture /* hpur TCcRIA=0x00; TCCRlB=0x0?; TCNTlH=0x00; TCNT1L=0x00; ICRlH=0x00; ICRIt=0x00; Edqe */ '/ off on Fallins Edge OCR1Ai,=0x00; OCRIBg=0x00; OCRLBI=0x00; /* /* External hler.upt INTo: On (s) ' / initialization lNT0 Mode: Any change INT1: Off on any chanqe /* Tnter.upE /* fnterrupt on any change on any cha4se /* Idterrupt EICRA=0x01; /* /r on pins on pins oD pins PCINTo-7: off PcINTa-14: off PcINTl6-23: off */ Ptoj?tt D"u?tapnP 1t EIMSK=0x01; EIFR=0x01; IlterrupE{s) /* Tine!(s) /CounEer(s) TIMSK0=0x01; TIMSKl=0x00; TIMSK2=0x00; iliEialization '/ UART idltialization /* /* comunication /* UART Receiwer: Paraneters: /* uaRT T'ransnitter: 8 Data, 9600 /* AnaLogr Conparatsor initialization A o_oq Compdrctor: Off Input Analos Conparator Capture /* ADc initializatiod /* ADc clock ' frequency: 31.250 Reference: /* aDc voltage ADMUX.FIRST ADC INPUTIADC avcc by Tiner/Counter */ VREF TYPE; watchdos Tine! inirializarion /* I'ratchdos Tine! Prescaler: osc/1024k interlupc: off /* watchdog Tine! +praqna oplsize + ifdef +pragna /* OPTIMIzE optsize+ G1öba1 enable /* /* these a few /* is SIzE instructioDs cPu cycles, temporarily interrupts 1: */ kIIz pin /* WDTCSR=oX39; wDTcsR=ox29; */ No PariLy on /* uaRT Baud rare: UCSR0A=0x00,. UCSR0B=0i48,. UBRR0L=0x19,. UBRR0H=0x00,. /; 1 stop, off nust be wichin so optinizalion */ disattled */ */ Off */ 347 3,1t| Sincethe A\rR processors areall very similar in capability,it is simpleto moveor "port" the code from one A\aR to another.To move the AIMegal6 code to the AIMega48, we automaticallyg"in the functionality of the USART and ADCs with virtually no changes whatsoever. Th€re is a smallditrerencein howTIMERl is handled. On the AIMega48, TIMER1 is in an upperaddress within the registermemoryspace. This m€ansthat the Code\tsionAvR compiler doesnot provide for a direct 16-bit accessto TCNT1. Performingtwo 8-bit accesses and combiningthem for the 16-bit resultcan easily overcomethis. To accomplishthis, the intem4t routine that readsthe wind speed counteris modfied asfollows: /i liner inlerrupl T static 0 owelfloq interrupt service routine ovf isr{voial) tTIMo OvFl void linero unsigrned inr */ TcN'r1 = 0; TCCR1B=oXoo;/* sEop counter ho prewent rollover TCNT1 = ( (unsisned ioE)TCNTIH) << 8; TCNT1 l= ((lun6isned int)tCNTlL) & OXFF); TccRlB=0x0?; /t sEart counEer aqaln */ if (++vind_tes!l)ass > 244) durins read "/ /r pass /r /' reset counter for next sanple.. reseE pass counler */ /* tine count tefore wind */ speed seple t TCNT1 = 0; wind test pass = 0, wind speed /= 2; RF TX Tine = 1; Eo EransniEl ! */ */ J A local variable TCNT1 is createdto hold the 16 bit counter value. The TMER1 counter is stopped during the read to prevent the counter from changing while it is being read,yielding a bogus result. Once the two 8-bit reads are performed, the TIMER1 counter is reenabled and everything continues on as usual. Other Considerations There are a few other differences fiom the ATMegal6 and the ATMega48. It is these differences that reinforce (the fact) that reading dre datasheet is a critical step in the development and support of software. As Atmd f,nds better ways to do things with AVRs, those features will be incorporated into their parts. Atmel made a few changes to the clock-oscillator circuits on the ATMep48 that are not currently in the AIMega16. So you may have noticed a couple ofunique items in the initialtation process. aliwision factor: 1 r/ /* Crysral oscillator +pragna optsize- Prbjert Deu/a?nent CiRPR=o:So; /* these CLKPR=0Xoo; /* wiLhln +ifdef _OPTIMIZE +pra9rna op.saze+ /* is SIZE lnstructions nusE a few CPü cycles, benpolarily alisabled be t/ so optinization t/ */ The AIMep48 has many clo& con6gurations to support a wide vari€ty of oscillator options as well as low power modes ofoperation. One of the features is a clock pr€scaler that allows the s)ßtem clock to be divided down to reduce the power consumption of the processor by tunning it slower In order to guarantee a glitch free change in the system dock whiJe changing the prcscale, it is rcquired that the CLKPR register be enabled and modified within four s;stem clock cydes- To guarantee this gpe of timing within the CodeVisionAVR compiler, the optirnizer must be disabled. This causesthe compiler to generate the assignment instructions in-line änd to reduce the potential of the optimizer inserting a call or jump insüuction between the ässignments. The samegpe of assignment rule applies to the watchdog timer aswell: l'iarchdos /* . ,crc\dos Tiner initialization 6 mcr p.es.ale.: osc/1024k Tiner inteftupt: off /* ifalchdoq *pragma optsaze*asn ( wdr" ) nust be wilhin WDTCSR=oX39; /" these instrucLions so opt in:ze. ior xD,CSp_or2o; /, ä taw cpu .y.tes, */ disabled /* is Lemporarily +ifdef +prasna _OPTIMIZE optsize+ */ , SIZE In order to guarantee that the watchdog timer was not simply disabled by errant code running wildly through memory the "two assignments within four cycles" rule applies here as well. You can seethat it is realistic iri many casesto move from one processorto another in order to add or reduce features, imprcve unit cost, improve performance, or reduce power con sumption. In many cases,a move like this can be performed in a few houß with very üttle impact to the entire desgn. 5.7 CHALLENGES Listed below are various features that could be added to or changed in the software to eniance the weather monitor operation and performance: . Add year and leapyeär träcking. . Add weatheralarms,asdiscussedin S€ction5.6.7,"SoftwäreDesign,Indoor UniC' 349 350 Add äverägint to the wind speed and rainfall measurements to make them more stable Add linear interpolationto improve the wind chill and dew point calculätions. Rainfall tracking: instead of todat this month, this Fa|! make the system tra€k rainfall in terms of the läst 24 hours, the lasr 30 days,and the last year to date. Track and indicate barometric pressure chänge rising, fälling, änd steädy. Add softwär€ to send the display information to a PC using the serial port and Enhancethe software to accept commands from a rc using a softwäre USART r€c€iv€ on the lNTo pin. Add logglngcapabilityto trlck peakwind, räin,temperature,and pressureconditions änd when they occurred.Allowthe user to view them on the displayor download Makethe m€a5uringfunctionsof the monitor a state machine,suchthat time/date editingand alarm set poim adjustmentsdo not imp€dethe normal operation ofthe 5.9 CHAPTER SUMMARY In this chapter, project development has been approached as ap,.rda$,an orderly set ofsteps that, when followed, wi11virnrally alwals lead to successfulproject. The processhas beeü demonstrated by the development ofa weather station based on the Atmel Mega16 microcontroller. 5.9 EXERCISES I . List eachof the stepsof the processof proi€ct d€velopmentandgiv€ an exampleof the activitiesthat would take placedurinSthat st€p (S€ction5.4). 2. In whichstepof the proi€ctdevelopment prccesswouldeachof the followingoccur (sections.4)l A. Prototypinga sensoränd iti conditioningcircuitry B. SimulatinS a circuit! op€ration C. Creatingdetailedspecmcatjons for a project D DrawinSa project schematic E. Testingindividualsoftwärefunctjons E Wrif ng softwarenowchans G. Testingthe final proi€ct to its specifications H. Doing proof-of-concepttening on a questionablecircuit Ptuje.t D.Lelofne,t 3 . UsinSthe table databelow write a proSrämto perfrcrma look-up-tableand linearinterpolationoperationto return a compensatedtemperaturefrom the ADC read;ng fsection 5.6.| 2): ADCVoluq, t0 Bt'|s(o-t023) 723 344 57a 765 492 1002 5.I O LABORATORY 20 0 20 40 60 80 ACTTVITY The only laboratory activity that is really appmpriate to this chapter is to demonstrate the processofproject development by developing ä projecl Some suggestedprojects are shom below. Any ofthese ideas could be modifred or expandedtluough tie use ofdisplays and,ror additional sensorsor inDut devices. | . A robotic"mouse"that canfollowblackelecüicaltaDeon a whitishvinvlflooiThis proj€ctwill requirecontrollingthe sp€€dandsteeringaswellassensing the blackline. 2. A devicecomposed of t]|e microcontroller anda videocämerathat cand€tectsimple shapes suchäsä square, a triände,or a circleof blackpaperon a white surhc€. 3. A deviceusingmotors,sensors,and a cardboardarrow to point to and follow a heat sourceas it movesabout the room.Thisdevicewould makeexcellentuseof steDDer 4. A replacementfor a fumac€tl€rmostac 5. A securit/ systemfor an automobilewitn sensoß to deted doors beingopen€d (includinS the gastankcoveithe trunhändt]|e hood)ändthät wouldd€tectwhen the vehicleis beinsmoYed. 351 Library Functions Reference I NTRODUCTION Much ofthe programming porver and convenienceofthe C languageJiesin its builtin, or library, tunctions. These are routines that accompJish many of the more common tasks that face a C programmer. As with all C functions, you call the librarv functions from your code by using thc function namc and cithcr passing values to the function or receiving the values re turned by the function. In ordcr to makc use ofthe tunctions, the programmer needs to know what parameters the tunction is expecting to be passedto it and the nature of any r':rlues returned from it. This information is made dear by the protogpe for the tunction. The tunction protogpes are contained in a set ofheader fles that the programmer"includes"in the code. There aremany library functionsa\,äilablein most C compilers,gatheredinto groups by tunction.This groupingavoidshaving to ;ncludca whole host ofunncedcd tunc tion prototypes in every program. For examplc, thc function protoq?es lor thc group ofroutines concerned with the standard input and ougut routincs arc contxincd in a header filc called stdio.h. If programmers wish to use some ofthese tunctions, they would put thc follow;ng stxtcmentinto the beginningoftheir code: +i n c l u d e <stdio.h> With the headerfile included. the tunctions concernedwith standard I/O such asthe pr;zffunction (refened to in earlier chapters) rre made available to the programmer This reference section describes each of the librar.v tunctions available in CodeVisionAVR. A comprehensive Jist, grouped by then header lile names, is followed by a detailed description and example of each funcrion, in alphabeticll order. 353 354 FUNCTIONS LISTED BY LTBRARY FILE bcd.h unsigned unsigned cha! bcd2bin(unsigneal char n) cha! bir2bcal {uns iqned char n) crype.h unsisned unsisned unsigned unsigned unslgned ünsigned unsigned unsigned unsiqned unsigned unsisned char char char char char char char char char char char i6alnun{char c); isatpha{char c); isascii{char c); iscntrl{cha. c); isaliqit {char c); islower { cha. c), ispiint{chär c), ispunct i char c), isspace (char c); isupper (char c); isxdigir (char c); char rolower{char c}; cha! roupper{cha! c}; char roascii {cha! c} ; delayh void void delay_us (unsisrneal inE n); delay ns (unsisneal int n); Srayh unsiqned char qlay2binc (unsiqneat char n); unsisned inE sray2bin (unsisned int n); unsisned lonq qray2binl (unsiqneal tonq n) unsiqned char bin2qrayc (unsisneal char n) unsiqned int bin2sray (unsiqned inr n) ; uns.iqned ]onq bin2qr-y](unsignecl lonq n) j math.h !nsignad .har .abs(signFd chdr x), unsigned lons labs (1ons x); float fabs (f1oat x) ; signed cha. cnax{signed char a,sisned int nax{int a, int b); long lnax (1ong a, long b) ; fLoat fnax (floac a,float b),. sierned char cmin(sigrned cha. a,signed int min(inr a, int b); lonq lnin(lonq a,1onq b); floar fmin(f1oat a, floaL b); char char .lppe signed char csigrn(siqned signed char fsisn(float char x); x); char isqrt{unsiqned int lsqrt(unsigned unsigned x), floal sqrt(f1oat inl x); lonq x) ; unsigned float float fLoat float x) ; floor l float i) ; ceil (ftöat fnod(f1oat x, ftoal nodf (f1oat x, floaE float float ldexp(f1oat frexp(f1oar floal exp(f1oat floa! float float flöaL float 1og(ftoar x); 1o910 (f1oat x) ; po0 { float x.floaE sin { ftoaE x); cos (ftoaE x) ; x); lan (ftoat ftoar sinh ( floar x); float cosh(f1oat x); f1öat Lanh(floaE asin (ftoaE acos (f1oaE atan (float atan2 (float x); floaL float float fLoar fLoar x,inl x, int ix A-Library y); *iparE) ; expon) ; *e).pon); x); y); x) ; x) , x); y, float x) , mem.h pokeb (unsigned inE aalall,unsigned p o k e w ( u n s i g n e d i nt adldr, unsigned woid p e e k b ( u D s i q n ed int äddr) cbar unsisned void unsisned int peekw(unsiqned int adalr); sleep.h void void void woid void void sleep disable (woid) ; idle (void) ; powerdovn (void) ; powersave (void) , srandby(void); ev t e rdcd_ sl d nctby (voiol , spi.h unsigned cbar spi (unsisrned char data); Ftnction! Referen.e 355 356 stdio.h void void geEchar (woid) ; puEchar (char c); purs (char rsEr) ; void char puts f (char *seEs(char void void printf char spri4tf signed char siqned char void void *str); flash rsE!,unsiqned (char flash (char 'sLr, scanf(char sscanf(char vprinEf{char ftash *srr, vsprinEf(char *fntsr!) char flash *str, idr ten); ; ifmrsrr); flash 'fnrsrr); cha. flash *fnEsEr, va_1isr chär ftash *fnrsEr); argprr); rfnrsrr, va1 tist arspr!); stdlib.h atoi {char tsE!) ; lons arol (char *sr!) , floar atof (char rsrr), lnt itoa(int n, char *srr); istr); ltoa{lonq int n,char asrr) ; ftoa(float n,unsiqned char decinals,char ftoe(f1oat n,unsigned char alecinals, char *str); void srand(inr seed) ; lnt rand (void) , *nal1oc (unsis.eal void inr size) * ca]1oc (unsisned void inr nun, unsisneal inr size) *realloc(void rprr, void unsiqneal int size) woid free (woid *ptr) void void void void string.h char *sErcat (char *str1, char *srr2 ) ; *strl,char char ,srrcatf(cha! flash *srr2); char rstlchr {cha. *srr,char c), signed char strcnp (char rsLi1, char *srr2 ) ; signed char strcnpt (char 'sr.1,char flash rsrr2); char *strcpy (char *alesr,char *src); char *strcpyf(char idesr,char flash rsrc); *srr,char *ser); unsigned char st.cspnichar unsigned chai strcspnf(cha. *srr,char flash 'ser), unsigned int strlen (char rsrr); unsigned inr srrlent (char flash *sEr); char *strncat (char *sLr1, char *srr2, unsisned char n) ; char *strncaEf(char rsrrl,char flash *srr2,unsiqned char a) ; *srrl,char rsEr2,unsisned siqned char scrncnp(char char n) ; sisned char sErncnpf(char *srrl,char flash *srr2,unsiqned char n) i rdesr,char *sxc,unsiqned char lstrncpy(char char n); char *strncpyf (char rdesr,cha. ftash rsrc,unsisned char n); Atlcnd;. A-Lib rt F|n.tiant R.f.rcrre cnar'sLrpbrk(chdr'sLr,chd!'set, ; llash'set): char'sLrpbrkflch"' sLr,chdr char -Llpos'chdr'str,cha' c): 'scrrch!(cha! 'sL r, chd ! c'; cn.r _4ar'sLr!pb!k{cher'sL!,cldr'set) cnar 'sLrrpb!kt{chd' str,chdr ; llasl_ set); siqned cha! sL!rpos(chdr'str,chd c); .ha!'sElst!(cher'strl,chdr'sL12l; 'strl,char ftash *srr2); char *stlsErf(char _ ' s p r ' s L t /seL); ( . h d q dt sr -rs ed ,.hdr rsF ) r 'slr,cl-dr fläsh -r s q,ed cler sl spnf(chdr ' s t r t o k ( c h a r ' s t r l , c h a r * s t r 2 ) ; flash char 'sr.,.hdr 'dcsl ,void ne-ccpy(!o'd c,ulsigned n): ,o d t n e n c h . ( w o i d t b u f , u n s i s n e d char c,unsigneal n); void *bufl,void *buf2,unsigned n) ; sigraed char nencnp(void * b u f l , w o i d *buf2,unsigned ( w o i d flash siqned cha. nencnpf *nencpy(void *alest, voial *src,unsigned void n),. * n e n c p y f ( v o i a l *dest,volal *src,unsiqned vold flash n); *nemove(voial *dest,rold *src,unsiqned void n) ; *nenset{voial *buf.unsigned void char c,unsigned n); n); abs #include <math.h> unsigned int ab(int x); unsigned char cab(signed char x); unsigned long labs(long x); float fabs(float x); The atu functioo returns the absolute mlue ofthe integet *.The eabs,labs, aÄfabs trnc tions return the absolute value of the signed char, long, and float rariable r: as an unsigned char.unsigaedlong. and float value,respectrvely. Returns: Absolute value of;r sized according to the function called + inctude <malh.h> void nain ( ) unsiqFed u s iqned // intjos 'n! lonq intl)os_v"l ; lonq_pos_väl; vatue of seL absolute va1 = abs (-19574) ; an inteqer 3s7 358 // qet absolute vatue of a lonq long pos va1 = labs{-125000); vhi re (1) I J ] Results: inljos vat = 195?4 long pos va1 = 125000 acos #include <math.h> foat acos(float x); The arasfunction calculatesthe arc cosine ofthe floating point number r. The result is in the rmge of -n/2 to n/2. The variable r must be in the range of-1 to 1. Returns: acos(x) in the range of 42 + include to nl2 where x is in the range of-1 to 1 <nath. h> floaL new va1; naw val - a.os (0.8?5) , whi le (1) i ) Results:new_val= 0.505 asin #include <math.h> float asin(float x); The arä function calculatesthe arc sine ofthe foating point number;r. The result is in the rzrge of -tJ2 to tr/2.The variable x must be in the range of 1to 1. Returns: asin(x) in the raoge of -tt/2 to n/2 where x is in the range of-1 to 1 +include <nath-h> A??e"d;r,4-Litrurr floaE Funct;ons Referen.e new wal; new val - dsin(0.8?5); whl te ( 1) { J ] Results: new_r*l = 1.065 atan #include <math.h> float atan(float x); The araa function calculatesthe arc tar:gent ofthe floaring point number * The result is rn the range of -r/2 to ztl2. Retums: atan(x) in the range of 42 +include void to nl2 <nath.h> nain ( ) { float new vat,. new val - äran( l.l4s); whi 1e ( 1) ] ) Results:new-r.a1= 0.852 al,an2 #include<math.h> float atan2(floaty, float x); The atan2finctton calc'.latesthe arc tangentof the floating point numbenl. is in the rangeof n to n. Retruns:atan(y/x)in the rangeof--zrto n +include void <@th-h> nain{ ) The result 359 160 tloat new va1; new va1 = atan2(2.14, 5-121 , Fhi 1e (1) { j ) Results:new val = 0.428 atof, atoi, atol #include <stdlib.h> float ato(char *str); int atoi(char*str); long atol(char *str); The aro/function converts the ASCII character stdng pointed ro by rft to its floating pornt equivalent. The aroi and arolfunctions convert the string to an integer or long integer, re spectively. A11three functions skip leading white spacecharacters. Numbers may also be precededby + and - signs.Valid numeric characters,re the digits , through 9. The tunction arorfalsoacceptsthe decimal point as a valid numeric character. Once a non white spacecharacter is encouotercd, the conversion to a numeric equivalent starts.The conversion stops when the first non numeric character is encountered.If no numeric charactersare found, the functions rctum zero. All three funaions return signedvalucs. Returns: . atol atoi, andatol return zero if no num€ricdatais found r atof - floating point equivalentof the ASCIIsüing pointed to by stt . atoi signedinteg€requivälentof the ASCIIsrring point€d to by srr . atol- sEnedlon8integerequivälent ofrheASCllstringpoinr€dto by str + include <nega16.h> +include +include <stdio.h> <std1ib.h> // this Lo include ' qu"r tz ^!/sl äl t c q u P r . Y ' H z| ' / +define xrat ?372000L /* Baud rare '/ #define baud 9600 putchar and prinrft Ftn.tia zryPendir r{-L;b4rJ MAX_ENTRY_LENGTS +define void Referen.e 10 nain(void) { nyslr char /* I MÄX_ETiITRYLEliIGl'g+l],' the USART's baudt rate initialize */ U B R R L = x r a l/ 1 6 / b a u d 1 ; reqisrer t s h e U S A R Tc o n t r o l /* initialize n o i n t e r r u p t s , I data birs RX & TX enableal, UCSRA=0x00; UcsRB=0xD8; ücsRC=0x85; while i/ (1) putsf('Ente! a signed inEeqer nunber followed by l\n\r"); (c < l{Ax ENTRY LENGT11) while { = qeEcharo; nystllc++l // qaiL fot a character rhen quitl // it \a is our te.ninaEinq' character, = = ( n y s t r l c if 1l ! ) break; ) myst!tcr - myinE = atoi(nystr); printf ("Your // integer fha lpminälF null // \0; value sElirq converl is: 8d\n\r',nyinL) ; Results: The following is transmittedby the USARL Enrer Once '!' a siqned inteser duntler fotlowed by I is received,the string is converted änd the result is transmitted to the USART. bcd2bin #include<bcd.h> unsignedcharbcd2bin(unsignedcharn); T\e bul2bin tuncl:on convertsa binary codeddecimal(bcd)ralue to a binary value.In br nary codeddecimalrepresentation, the uppernibble ofthe wlue representsthe 10sdigit of 361 362 a decimal 1"1ue.The lower nibble of the value represerts the 1s digit of a decimal value. z must be a value betlve€n 0d and 99dReturns: Bina:y value ofz <bcd-h> +include void nain ( ) unsigned char t'cd ra1ue, bin value; bcd value = 0x15; /* bcal representation bin value = bcd2bin(tcal value); of decimar 15 */ {hi 1e { 1) t t ) Results:bin_value= 15(=ü,roF) bin2bcd #include <bcd.h> unsisned char bin2bcd(rnsisned char n); 'fhe bin2bcd tunctjor' anverts a binary value to a binary coded decirnal (bcd) ulue. In bi nary coded decimal represertation, the upper nibble ofthe value representsthe 10s digit of a decimal value.The lower nibble ofthe value reprcsents the ls digit ofa decimal value. z must be a l'alue between 0d alld 99d. Retums: Binary coded decimal value of z <bcd.h> +include void nain( ) { .nsisnpd bin_walue bcd_value while (1) t I ) Results: bcd-mlue = &15 .här bin välup, b.d value; = 0x0Fr /* 15 decinal = bin2bcd(bin value); a/ ,4?fe"dir'4 Libralt F r.tia Refer."rc bin2srayc, bin2gray, bln2grayl <gray.h> #include unsignedcharbin2sayc(unsignedchar n); unsignedint bin2gralunsigned int n); long n); unsignedlong bin2grayl(unsigned 'lhe tin2gra! functionsconverttlrc binary lalue z to a Gray-codedvalue.Gray codeswere developedto prevent noise in systemsu.here analog-to-digital conversionswere being performed.Gny codeshavethe advantageoverbinary numbersin that only one bit in the code changesbenveensuccessivenumbers.The bin2gray frncions bin2gm1t,bin2gm1, md bin2graylarc tailored for unsignedchar,unsignedin! and unsignedlong variables, respecnvely. Table A-1 lists the Gray codesarrd then binary and decirnal equivalentsfor ralues 0 throush15. 0 1 2 3 5 4444o 0000 0001 0010 0011 0100 0101 0ll0 G.oy Code Equivolent 44480 0000 0001 0011 0010 0110 0111 0101 0100 1100 7 0lll 8 10 1000 1001 1010 11 1011 1110 12 13 1100 1010 1101 1011 74 1110 15 1111 1001 1000 9 Table h-l 1101 1111 GtsyCodeEquivole,l/F of De.inal ondAnsryuolues 363 3U Returns:Binary r,ralueofz +include <gray. h> I unsigned char qray char, bin_char; bin char = 0x0?; erray char = bin2qray(bin char); while (1) l Results:gray_char= 4 calloc #include <stdlib.h> void .caloc(unsigned int num, unsigned int size); The ra1lacfunction allocates a mernory block in the ieap for an aray of num elements, each element having the length ofsizz b1tes. On retum, the function returns a pointer to the start ofthe rnemory block which is filled with zeros.The atlocatedmemory block occupiesrrc+4 bltes in the heap. This must be taken into account when specif,ing the heap size in the ProjecrlCon figurelC CompilerlCode Generation menuReturns: Ifsuccessful in finding contiguous frec memory ofthe appropriare size, retums a pointer to the mernory block- Ifunsuccesstul, rctums a null pointer +incLude <nega16.h> the standa.d /* include +include <stdio.h> ' fhF vä :dble clud+include #define +define input/outpur lensfh */ libraly dfsu-c-. l isrs md.ros <stdLib.h> xral 6000000[ baud 9600 // declarinq a pointer, bu! not struct lwo d *two dj; struct two-d *start Lwo_d_p; int nenory_size; reservins nenory for rhe arrayl ,4?fendi' I-L;brorJ Ftn.ti.^ Referente t J; void I main (woid) / / U S A R Ti n i t i a l i z a t i o n Paramelers: // Comunicatioo R e c e i v e r : on U S A R T // T r a n s n i t t e r : On U S A R T // M o d e : A s y n c h r o nous U S A R T // B a u d . a t e : 9 6 0 0 U s a R T // UCSrÄ=0x00; UcsRB=0xD8; UCSRC=0x86; UBRRH=0x00; UBRRL=xral/ 16lbaud 1; a Data, 1 Stop, shile {1) t pursf (' \n\rHow nuch menorl. shoulal r (scanf ( " td' , &nenory size) != -1) if if t ({nenory_size}sizeof(struct p' .! f('\n\rThänls, l'11 f itt? rwo d}) No PariLy ( E N " E R )\ n \ r " ) ; < ( _ H E A P _ S I Z E _- 4 ) ) tryl\n\!"); / / t.y Lo seL enoügh renory = starE-two-aL) twö_d) ) ; ca1loc {nenory size, sizeof (struct = start too dj; lso_dJ ( two_au) != NULL) if I printf ( " \n\rhitiat values!\n\t"); for (i=0; i<nenory size;i++) { printf ( '*04x g04x\n\r", rao-d-p >index, >watue); tro dj two d p -inclex >value - i + 1000; tro dj // change the value two dj++; // nowe the poinLer forwaldl ) 36s 366 printf ('\n\rModified values!\n\r') ; cwo all) = start_Ewo-alj; the ner walues! // prlnt for (i=0; i<nenory-size; i++) I prinLl ('904x t04x\n\!",tko d p-. .d.r. two_dL) >value),. forwarall // nove the pöinter I // free the catloc üenory free(slart two aL)) ; for next rimet ] prinEf{ "Failed to calloc collecrly.\n\rii); I t plintf('\n\rHeap size 1lnit is gd\n\r", HEApSrzE 4); J Results:The USARI transmits,xt 9600baud, How much nenory stlou1d I filt?(ENTER) Then it waits until a number is entererl followed by a nevline character Once this is re ceived (5 for crample), it transmits Thanks, I' 11 tryl Inirial values ! 0000 0000 0000 0000 0000 0000 0000 0000 00 0 0 0 0 0 0 Modlfied vatües ! 0000 0388 0 0 0 1 0 3E 9 0002 03EA 0003 03EB 0004 03Ec /1?fend;E)t-L;bu/r F n.tian' R.ferc"rc cabs #include <math.h> unsigned char cabs(signedchar x); Returns: Absolute value of* Seeabs. ."it #include <math.h> float ceil(float x); The ceuT function returns the smallest integer ralue that is not less thar the floating point number x. In other words, the reilfunction rounds r up to the next integer value and returns that value. Returns: Smallest integer value that is not less lhan the floating point nunber r <nath.h> +include void nain ( ) t float new vat; nes vdl - ceil (2,5lI), 0hi1e (1) t ) ] Results: new val = 3 cmax #include <math.h> signed char cmax(signed char a, signed char b); Returns: Maximum ralue of a or D cmtn #include <math.h> signed char cmin(signed char a, signed char b); 367 368 Returns: Minimum value ofa or / See nin. cos #indude <math.h> float cos(float x); The ras function calculates the msine of the floating point number a The angle x is expressedin radians. Returns: cos(x) *include <naEh.h> void () nain t float new_va1; new-wal = cos{s-121); whire ( 1) t t ] Results:new val = 0.397 cosh #indude <rnath.h> float cosh(floatx); The car,ifunction calculatesthe hlperbolic cosineofthe floating point number* The angle ,. is eYpr€ssed in radians. Returns:cosh(x) +idcluile void t <nath.h> nain( ) float new val; new wat = cosb(5.121); while(1) { l t Results:new val = 83.754 Af?erdir A L;trarr F"n.tiah' Refeftnrc csign #indude <math.h> siped char csign(signed char x); Renuns: -1, 0, or 1 ifa is negative, zero, or positive, respectivü Sees;Sn. delay_ms <delayh> #include void delay_ms(unsignedint n); The delal ns furcool' generatesa delay of rl millis€conds before retuming. The interrupts must be turned offärou rd tlrc callto the delal ns function or the delay will be much longer than intended. The actual delay depends on the dock cry*tal frequenry. Therefore, it is important to speci! the correct clock frequenry. This can be done either in the Projectl ConfigurelC Compiler menu or with the statement #def.nextal xI. where xL is the clock frequency in Hertz. Returns:None +include <delay.h> +incLude <nega16.h> +include <stdio,h> /* qüartz #define frequency crysEal ?372000t xral /a Baud rate baud +define vold [Hz] t/ i/ 9600 nain(void) { the UsaRT's baual laEe r/ /* inirialize UBRRH=0x00; UBRRL=xra1/16lbaud-1; t h c U S A R Tc o n t l o l t e q i s l - ' /- iniri-Ii7e I data birs Rx & '!x enableal, no intelluptss, */ 369 370 { putsf{"How nany mitliseconals s h o u l d I p a u s e ? ( E N T E R )\ n \ r " (scanf("*u\n',&pause if tine) != 1) t ( "Thanks ! I'11 prin!f pause for $u n i l l i s e c o n d s - \ n \ r " , pause crnej; // disable *asn("cti'); delay )t intellupts ns (pause rime); enabLe intserruprs // *asn( "sei'); Results: The microprocessor transmits How nany milliseconals should I pause? (ENT'ER) Then it waits untd a number is entered followed by ä newline character. Once this is received (2000, for example), it transmits Thanks! I'11 pause for 2000 nilliseconds. Then after an appropriate pause (2 seconds in our example), the 6rst prompt is again üansmitted. det"y "" #include <delay.h> void delay us(unsigned int n); The tlelay_usfnctton generatesa delay of z microseconds before returning. tl must be ä constant exprcssion.The interupts must be tumed offaround the call to the delal as fmction or the delay will be much longer than intended. The actual delay depends on the clock crystal frequency.Therefore, it is important to speci& th€ conect ctock frequency.This can be done either in the PrcjectlContrgurelC Compiler menu or with the sr^rement #deJ6ne xtal ttL, wherc xL is the clock ftequency in Hertz-. Returns:None +include <detay.h> +include <nesa16.h> +include <stdio-h> 4?end;, frequenct /* qualEz c.ystal ? 3 7 2 0 00L +define x!a1 * / /* Baud rate +define baud 9600 void main (woid) t unsiqned int A-Library F!"t,io's Refel.nce [Hz] */ pause_time; the USART's baud rate */ /* initiatize UBRRH=0x00; UBRRL=xtal/16lbaual-1 ; t h e U S A R Tc o n e r o l l e q r i s t e r /' initialize RX & TX enabled, no inrerrupEs, I dlata birs UCSRA=0x00; UCSRB=0xDa; UCSRC=0x46; */ t p u t s f ( ' H o w m n y E b o u s a 4 a l so f u s e c o n d s s h o u l a l I p a u s e ? \ r " ) ; püasf('Ente! a Durtrer between 1änal 5- Press ENTER.\n\I'); if (scanf {'8u\a". &pause_tine) != -1) { if t { (pause_tine prinEf{'I'11 pause_tine); > 0) && (pause tine < 6)) pause *1u000 nicroseconds. \n\r " , +asn('c1i'); { case 1: detay_us (1000) ; break, case 2. (Ielay-Ds (2000) ; break; case 3: delay us(3000); break,. delay us(4000); break; 171 372 delay break; defaulE: us (s000) ; break,. ) *asi{ "sei'); pursf{'Huh?\n\r"); Results: The microprocessor transmits Hov nany thousands of useconds should Enter a nunbe! between 1 anal 5, press r pause? ENTER. Then it waits until a number is entered followed by a newline character Once this is received (2, for enample),it transmits 1' 11 pause 2000nicroseconds. Then after an appropriate pause (2 milliseconds in our exanple), the tust prompt is again transmitted. exp #include <math.h> float e<p(float x); The ar2 function calculatesthe naural (basea), erqonential ofthe rriable Jt. Returns:I +include <nath.h> i floar ner wa1; n e w _ v a 1= e x p ( s ) ; { I tf?ed;, ,4-L;b/art Functian! Refele,.e e5 = 148.413 Results: new-l"I= extended_standby #include <sleep.h' void axtended standbl'ftoid); The exten.ledstantlb! firlrction puts the AVR microcontroller irto e{tended standby mode. This is a sleep mode and similar to t\e potondotaz function. Seepouedownin thtszppendixlor the funcrion rrse Seethe Atmel datasheetsfor the complete description ofthis sleep mode as it aPPliesto n particular A\rR device. E*ended standby sleep mode is not available on all A\tR devices. >fab9 #indude <math.h> float fabs(float x); Returns: Absolute value ofr Seeabs. floor #include <math.h> float floor(float x); The/aar function returns integer value ofthe floating point number:r. This is the largest whole number that is less than or €qual to t Returns: lnteger portion ofr <nath -h> +include float new val; new val vhile(1) t t ) Results: new-wl = 2 = floor(2.531); 373 374 f rnax #include .math.h> float fmar(float a, float b); Returns: Maximum ralue ofa or / fmin #include <math.h> float fmin(float a, float b); Returns: Minimum value ofa or / fmod #include <math.h> float frnod(float x, float y); The./zol tunction retums the remainder ofr divided byn This is a modulo function specif ically designed for float gpe Iariables. The modulo operator (%) is used to perform the modulo operation on integer wriable gpes. Retruns: Remainder of;r divided byy <nath- h> *include void nain( ) I ttoah renains; renains vhi te (1) t t ) Results:remains= 1.6 tree #include.stdlib.h> void free(void -ptr); = fnod (25.6, 8); '4??.,dir 2t Librarr Funrt;aa\ R.fercr.e They'aa tunction fteesrnemoryallocatedin the hezp by nalloc, callot,or real/r' tunctions and pointed to byy'h After being freed,the memoryblock is arrailablefor new allocation. Ifp;z is null, then it is ignored. Returns:None frexp #include <math.h> float frevp(float x, int *expon); They'af function returns the mantissa of tlle Oo3ting point number r., or 0 if r is 0. The power of2 exponent ofa is stored at the location poioted toby expon.lfr is 0, the value stored at r,.Pm is also 0. In other words, if the followiag call is made, y = frexp (x, expon),' the relationshpbetweenerc?or,x, ^nd the rcfurnvaluel canbe erpressedas Returns:Mantissaof;r in the ange 0.5 to 1.0 or 0 if:r is 0 +incLude <meqa15.h> +include <aath.h> void maia (void) I float x, z; float a, c; float d, f; y , = 3 . 1 4 1 5 9j a = 0 .14159; d = .?07000; 375 376 I J Results: I .141590 2 0.?85398 0 .141590 -2 d= 0.566360 0.?0?000 0 0,70?000 fsign #include <math.h> signed char fsign(float x); Returns: 1, 0, or 1 if ;ris negatir,€,zero, or posidve, respectivdy SeevS?. ftoa #include <stdlib.h> void ftoa(float n, unsigned char decimats, char *str); Thelaa function converts the floating point value z to its ASCII character string equi Ient. The value is represented with tlre specitred number of decimal places.The string ß stored at the location specified by *srr Take care to ensure that the memory allocated for rl,. is large enough to hold the entir€ lulue plus a null-temimting chrracter. Returns: None *tnclude <nesa16.h> +inctude <stdio.h> +include <std1ib.h> // crystal /' quartz frequency +define xral ?372000L /* Baud .are +define baud */ 9600 this [Hz] to include putchar and prinrfl ,4!2."dix A Librurt F"n,tiont Rel.renrc nain (woid) void char nystr[11]; */ the USART'S baud rate /t inltialize UBRRH=0x00; UBRRL=XLa1/16lb.aud 1; registei initiali.ze the USARt control /' no intetupts. I daEa bils RX & I'X enabled, */ UCSRÄ=0x00; UcsRB=0xD8; UCSRC=0x86; ftoa (12470 .547031, 2,nystr) point putsf('The floating ; value is: "); purs (nysrr) ; while (1) t J Results:The USART transmits,at 9600baud, -hF I oä ing poinE is vdlue 12410.55 ftoe #include <stdlib.h> void ftoe(float n, uflsigned char decirnals, char'str); Thefae function converts the floating point ralue z to its ASCII character string equiva lent. The valu€ is regesented as a mantissa with the specif,ed number ofdecimal places and an integ€r power of 10 exponent. The string is stored at the location specified by trl: Take careto ensurethat the memory allocated for rt is large enough to hold the entire rdue plus a null terminatins character. Returns:None +include <nega16.h> + include + include <stdio.h> // Elris to <std1ib.h> frequency /* quartz crystal 7 3 7 2 0 00L x r a l #define [Hz] include putcbar and printf! 377 378 /* Baud rate +define baud void */ 9600 nain (woid) /* initialize the USART'S taud rate '/ UBRRL=XIä1 /16/baüd-1 ; /* iditiatize che USART conrlo1 register RX & TX enableal, no inlerruprs, I data f Eoe(0,001247,2,nystr) ; puEsf("The poinr ftoatinq puts (nystr) , ,hi1e walue is: birs */ "); {1) { ) ) Results:The USART transmits, ar 9600 baud, "-c flodrjng poi.r vdLup js: I.25e a getchar #include <stdio.h> char getchar(void); The griclar function is a standard C languägeVO tunction, but it has been adapted to work on embeddedmicrocontrollers with limited resources.The garrlar fimctioo rcturns a character receivedby the USART This function usespolli ng to gei the characrerfrom the USART. As a result, the firnction wais indefinitely for a characterto be receivedbefore retuming. Prior to this function being used, the USART must be initialized and the USART receiver must be enabled. Ifanother peripheral is to be used for receiving, the gexbar tuncior. czn be modi6ed accordingly. The source for this firnction is in the srdio.h fle. Ifyou want to replace the standrrdlibrary gexbarwith your own venion, you must do three things. First, you must phce the new gethar fitnction in rhe .r 6le before including the ,1|?fendix [-L;t@rr F,n.tion: Refeftnte standard library. Second,you must follow the new geftlrar Ä]J'clion v'itll n defnition statement telling the compilet to ignorc ^r'y othet getetal frmctions that it 6nds. Finally, include the standud library Put togethet the code might appear as char setcbar (void) I // you. getchar routine statenentss here ] ALTERNATE GETCHAR <stdio.h> +dEfiNE +include the // rest of file! Lhe source The standatd gexbar| rcturns: char received by the USART +include <nesa16.h> +!nclude <stdio.h> ' qud'. z cJlsral fraquen.y ?3?2000L +define atal /* void '/ */ Baud rate baud #define tHzl 9600 nain(void) { ,/* initialize UBRRE=0x00; /* inirialize USART's baud the register USART control no interrupts, a data Rx & Tx enabled, rate */ the bits */ UCSRA=0x00; UCSRB=0xD8; U C S R C = 0 x 86 ; while (1) t the /* .eceive k=qeEcharO; /* and echo it putchar (k) ; charäcter back */ t/ ] Results:Charactersreceivedby the USART areechoedbackout ofthe USART until power is removedfrom the processor. 379 380 *gets #include.stdio.h> char *gets(char *str, unsigned int len); The .gerrfunction reads charactersftom the USART usingthe getcharfaac:jonuntil a new line chancter is encountered and places them in the string pointed to by Jlx The newl.ine character is replaced by \0'and a pointer to srr is retumed. If&z charactersare read before the newline characteris read, then the fnction terminates the string strwith '\0' and retums. Prior to this fünction being used,the USART must be initialized and the USART receiver must be enabled. Returns: Pointer to the string rrr #include <neqa16.h> +inctude <stdio.h> c.ystal frequency /* quartz +define xral ?3?2000L /* Baud rate +define baud tHzl '/ toon lor */ 9600 nain (void) void 1 cha! you! nämetlll, // l0.h- s plus r/ the usaRT's baud rate /* initiatize UBRRH=0x00; UBRRL=xrat/16/baud-1 ; the USART control resistser /* initiatize Rx & Tx enabled, no interrupts, 8 dala UCSRA=0x00; üCSRB=0xD8; UCSRC=0x86; puLsI("P]ease anrer your nee dnd p ess pursf (.(onty 10 characters are allowed)\r,,); geEs(your nane,10); // up to 10 chars! p!inE f {" Hi gs ! \n \ r', you r_nde } . { ) biEs te.ain"(ior r/ A?f edi, ,4- Librrlr F"n ians Refere"te Results: The USART transmits the prompt for a name: Please enler your nane anal press return(OnLy 10 characters are alrowed- ) Then the microprocessorraaits for either a newline chäracter or 10 chamct€rsto be received by the USARL Assume the sting lane Doe" is received followed by the newline charactcr The following is transmitted: Hi Doe ! Jane gr^y2binc, gr^Y2bin' SraY2binl #include <gray.h> unsigned char gray2binc(unsigned ch,r n); unsigned int gray2bin(unsigned int n); unsigned long gray2binl(unsigned long n); The gray2bin functions convert the Gny-coded decimal value z to a binary coded mlue' Gray coäeswere developed to prevent noise in slstems where analogto-digital-conversions *"re being p.tformed. Gray codeshave the advantageover binary numbers in that only one bit in the iode changes between successivenumbers The gmy2bin functrons gral2bne' gray2bin, and,gral2bint are tailored for unsigned char, unsigned int, and unsigned long var ables,respectively. Table A-7 ir,the bin2gray function description lists the Gray codesand their binary equivalents for values 0 through 15. Returns: Binary r"alueof z + iEclude <erray.h> i unslgned char glay-cha! oi _.här I ] ) bin char= Results: idte #include <sleep.h> void idle(void); - qlay-cha!, bin-cha!; = OxO4, /r sray representation .hd!) i ordy2bin(otdy of decinal 7 */ 381 382 The //e function puts the AVR mrcrocontroller into idle mode. The 6mcnor. nee?_enabk must be cälled prior to this function being used.In idle mode, the CPU is stopped, but the timervcounters, watchdog timer, and t]rc interrupt s'stem continue to run. As such, the microcontroller can wake up ftom either idtemal or er.temal interupts. Upon raking up from an interrupt, the MCU executesthe intemrpt and then continues executing at the instruction following the sleep command (called by the idlz lhnction). Returns: None Seeslee, erurblefot a code example. isalnum #include<cqpe.h> unsigned char isälnum(char c); The ialnum funcircntests r to seeif it is an alphanumeric character. Returns: 1 ifr is alphanumeric +include <c!tpe-h> { -,s'o cd .h-. c_a1nun_flaq d_alnun_flaq ._dlnum_._aq, = isalnu( 1 ); = isalnun(1); d.dlrun I]dqr // lesl rhe ASCII // lesr rhe value { ) J Results: c alnun flag d-alnun-flas = 1 = 0 isalpha #include<cgpe.h> unsignedcharisalpha(charc); 'fhe isalphafuiclton testsr to seeif it is an alphabeticcharacter. Returns:1 ifc is alphabetic +include <ctype.h> value 1 of 1 (0x31) Äfiend;. A-Lib4rt F"sctian' R.fereace nain () void I . ,iq pd.hd c_a1pha_fLas d_alpha_flas whi 1e (1 ) ._dlp\d_rldq, = isalpha('a'); = isalpha('1'); d_alpha_r_ds: // // Eest rest the the aSCII character 'a ascrr character 1 { ) ) Results: c atpha d atpha flag flaq = 1 = 0 rsascrl #include<cqpe.h> unsigned charisascii(char c); The e,a,riitunction testsr to seeif it is an ASCII character.ASCII charactersrangefiom 0d to 127d. Returns:1 ifc is ASCII <ctype.h> main ( ) +include void { unsrqn-o chq! c dsci i lldq, d ds.ii c ascii flaq = isascii( a ); // = isascii(151); d_ascii,fLaq // Llcs; test the tesE ASCII Ehe walue charactser a 153 whiLe(1) Results: c ascii d ascii flag flaq = 1 = 0 tsc'ntrt #include <cqpe.h> unsigned char iscntrl (char c); The is,zal function tests r to se€if it is a contol character.Contml characters range fiom 0d to 31d and 127d. 353 384 Returns: 1 if r is a control character +include <ctype.h> { unsigned char c-iscnrrl flas, d_iscnrrl flag; c iscntrl_flas = iscDLrl('\t'); // resr rhe control = iscntrl('a'); d iscnt.t_flas whi 1e (1) { // // cbaracLet, horizonlaL tab test the AscII chalacrer a j Results: = 1 = 0 c_iscntrl_flag d_iscnt!1-f1aq isdlglt #indude<cqpe.h> unsignedcharisdigidcharc); The isligr'rfunction testsr to seeif it is anASCII representationofa decimaldigit. Retums:1 if r is a decimaldigit #include <clype.h> t unsisned char c isdigit_flaq, d isdigit_flas; c_isdisiE_f1ag = isdisit('1 // test the ASCIr characrer 1 ); = isdiSit('a'); d isdisit-f1ag // test the ASCrr chaxacLer a t ) Results: c digit d digit flas ftas = 1 = 0 islower #include <cqpe.h> unsigned char islower(char c); The ü/oaer function tests , to seeifit is a lowercasealphabetic chrracter App.ndi',4 L ' b r a t r F u n , t i a n t R e J ? . ? 1p Returns: 1 if r is a lowercasealphabetic character +include <ctype.b> { unsiqned char c istower flag, d_islower flag; = istower( c-islower_flaq A'); // Eesr rhe ASCrr characler r. d islower_flaq = islowe!( a')r // Eesr rhe ASCrr character. whl1e (1) I ) J Results: c isloFer d isLower flaq fLag = 0 = 1 isprint #include<cgpe.h> unsiped char isprint(charc); The lrynzr function tests , to seeif it is a pintable character-Printable chuacters are be tween32d and 127d. Returns: 1 if r is a printable character +include <clype.h> unsiqaed c_isprint d_isprint char flas flas c_isplinr_ftaq, d isprinE flag; = isplint('a // tesE rhe ); = isprint{0x03); // tesE rhe // characler, { ] l Results: c isprint_flaq d isprln!_flaq = 1 = 0 ispqnct <cgpe.h' #include unsigned char ispunct(char c); ascrl characrer control backspace a 3A5 386 The ispunx nc6on tests r to seeif it is a punctuation character-All chrracters that aie not control characters and not alphanumeric characters are considered to be punctuation Returns: 1 if r is a punctuation character +include <ct}.pe.h> I unsigned char c ispunct flag, aI ispunct_f1as; c ispuncr flaq = ispüct ( ,'); // test the ascrr character, coma d ispuncr flag = ispunct( tab \c ),. // test rhe horizontal chataeter // whi re (1) I ) Results: c ispunct d ispunct flag flag = 1 = 0 isqrt #include<math.h' unsignedcharisqrt(ünsignedint x); Returns:The squareroot ofthe unsignedintegervariable* Seer4. rsspace #include<ctype.h> unsignedcharisspace(char c); The irTacefunction testsrto seeif it is a white spacechancter.Characterssuchasspace, line feed,and horizontaltab areconsideredwhite spacechascters. Returns:1 if r is a white spacecharacter + include <crype.h> unsisned char c_isspace_flas, c isspace Elag = isspace('Ä') ''""'); j dl_isspace_f1as; // LesL rhe ascrr character /t rcsl Lha l-o- /olLa oo / | aliät ärt ä' A 4 ?2.n.ti. .4-Lib/art F nrtions Refel.üe { ) ) Results: c isspace ffas = 0 d isspace_f1as = 1 rsupper #include<cgpe.h> unsiged charisupper(charc); 'fhe isupperfunction testsr to s€eifit is an uppercasealphabeticcharacter. Returns:1 if r is ar uppercase alphabeticcharacter +include <ctype.h> t .hu_s gn-d ' '..ooe'_fl"q d c_ - -.oo-'_-l-o suppe! isuppp!{ 'suppe!{ tlag, d isuppe._' _dqi A'l' // les. rhe ASCLr (hd!d^rp! A d // lcsl tha ASC,r chq!a^cer a l; { ) J Results: c-isupper d_isupper flag ftag = 1 = 0 isxdlglt #include<cq.pe.h> unsignedcharis{digit(charc); The i*/ig:r tunction testsr to seeif it is ar ASCII representationof a ha'radecimaldigit. Returns:1 ifr is a hexadecimaldigit +include <clype.h> unsigned char c_isxdiqit ftaq. d c isxdigit ftaq = isxdiqir( a ). = isxdisir{ d isxdigit_flaq z ); isxdisit_f1as; // test the the // test ascll ascll characrer charactser a z 387 388 { ) Results: c isxdiqiE d isxdiqic = 1 flaq = flagr 0 itoa #include <stdlib.h> void itoa(int n, char *str); The r'raafunction converts the signed integer value z to its ASCII character string equivalent. The string is stored at the location specified by *rt Take care to ensuretlat tle memory allocated for rlr is large enough to hold the entirc ralue plus a termination character. Retuns: None +include <neqra16.h> +lnc1ude <stdio.h> +include <sEdlib.h> // Ehis freqoency clysta1 /* quartz +define xEal 7372000L /* Baud rate baud +define woid to include lEzl putchar and printf! '/ +/ 9600 nain{void) t cbar nyst. [10] , */ the UsART's baud rate /" iditialize üBRRE=0x00; üBRRL=xtal/16lbaüal-1 ; the usÄRT control register /* initlalize Rx & Tx edableal, no lnteüupts, a data UCSRB=0xD8, UCSRC=0x86, itoa(-1231,nystr); putsf ('Tbe vatue is: \r" ) ; bits */ ,4Lf.ndi' 4 0hi1e I ] Libr'lt Fti.tianr R+r.4ü (1) ) Results: The USART trarsmits,at 9600baud, The walue -123L is: labs #include<math.h> unsignedlong labs(1ong x); Returns:Absolut€valueof* Seeabs. ldexp #iadude <math.h> float lderp(floatx, int expon); The /1ex2functior calculatesthe valueof* multiplied by the resultof2 raisedto the power RetuJns:,' * 2*P'" +inctude <narh.h> t new va1 = lalexp (5,3) ; whi 1e ( 1) { I ) Results: aew-val = 5 *23 = 40 lmax #include <math.h> long lrnax(long a long b); 389 390 Returns: Maximum value ofa or , #indude <math.h> long lmin(long a, long b); Returns: Minimum value ofa or ä Seemin. t"s #indude <math.h> float log(float x); The /ag tunction calculates the base a or nanral logarithm of the Ooating point value r. ;r must be a positive, nonzerc value. Returns: log(x) +inctude <maEh.h> t new_val = 1oer15) ; whi le ( 1) { ) J Results:new val = 1.609 loglO #include <math.h> float log10(floatx); The /ag70 function calculatesthe base 10 logarithm ofthe foating point value r. r'rmust be a positive, nonzero value. Returns: loglO(x) +incLude <ftach. h> Atuendtr A Liblatr Functian! Ref.ren.e float nev va1; new va1 = 10910 (5) ; whi 1e (1) I ) ) Results:new val = 0.699 lsign #include <math.h> signed char lsign(1ongx); Returns: -1, 0, or 1 if .r is negatirc, zero, or positive, respectively Sees/3a. lsqrt #include <math.h> unsigned int lsqrt(unsigned long x); Returns: The squareroot ofthe unsigned long variable * Seesgrt. Itoa #include .stdlib.h' void ltoa(long n, char *str); The äaa function converts the long signed integer value z to its ASCII character string equivalent.The string is stored at the location specified by ta Take care to ensurethat the memory allocated for srr is large enough to hold the entire value plus a null-terminating character. Returns:None +incLude <nega16.h> +incLude +include <stdio.h> <stdlib-h> // frequency crystal /* quarrz +define xEaL 73?2oool- Ehis to [Hz] include */ putchar and printfl 391 392 /* Baud rare */ +define baud 9500 void I main {void) char mysErtlll; Ehe USART's baudl rate */ /* initialize UBRRH=0x00; UBRRL=xtal/16lbaud-1 ; the gsART cont.ol register /' initialize Rx & Tx enableal, no intedupts, I dara bits UCSRÄ=0x00; UCSRB=0xD8; UCSRc=0x86; ltoa(120031,nystr); puLsl {"rhe lonq signed inrege! Puts (nystr) ; while t J value is: */ _ )i (1) ) Results:The USART transmits,at 9600baud, The _o-9 sisned inleset vdluers: t2aa11 malloc #indude<stdlib.h> void *malloc(unsignedint size); The nallor fu;;,cnor'dlocatesa memoryblock in th€ heapwith the length oflize bytes.On retufn, the fünction retums a pointer to the start of the memorybloclq which is filled with zercs.The allocatedmernoryblock occupiesrizr+4 bytesin the heap.This must be taken into accountwhen specifyingthe heap size in the ProjectlConf,grrelC Compiler Code Generationmenu. Returns:If successfirl in finding contiguousfree memorywith sr'zeb1tes,returnsa pointer to the memoryblock.Ifunsuccesstu!returnsa null pointer. +include <nega16. h> /* include the standard #include <stdio.h> input/ourput library */ L;ttult 4?e"dir.4 rhe variable /* include <std1ib.h> +include +define +define // xral baud lists nacros */ a pointer, but noE reserwiag memory for ihe arrayl cptr; s 1ze; nain (void) woid Refeftnte 6000000L 9600 declaring chax *start lnr nemory 1enstsh argunent Fu"ctian! t // // Comunication Parmete.s: USART Recetve.: On // USART TlansniEter: // USART tqode: Asynchronous // usaRT Baud raEe: UCSRA=0x00; UCSRB=0xD8; UCSRC=0x86; UBRRH=0x00; 8 Data, 1 Stop, No Parity On 9600 t putsf(i\n\rHow nuch nemory shoutd I iJ (s.-nr ("$d',!me-o!y size) l- -I) fill?(ENTER)\n\r'); t if (nenory_size < ( HEAP SIZE - 4)) { ('\n\rThanks, printf I' tt tly!\n\r"); / / Lry Eo .teE enough menoly = matloc (neno.y star!_cptsr size); .pl r - stdrt cpl !; (cptr if != NITLL) { printf for Values! \n\!" { " \n\rlnitial ( i=0, i<nenory_size; i++ ) t / /ptinL Printf the initial value ('902x ", *cprr) ; ); 393 394 'cpl r - (.harl i ! l; // .hange the J-lue ro 4ä-dl .pLr++; // nove the po a.e = = ( ( 0) if {i+1)810) printf ( '\n\r') ; ] printf { '\n\rl{odifleal values ! \n\r" cpt. = starf cptr; Llle neo valuesl // print for {i=0; i<nenory size; i++) t n n . ri r i c . r v , t u e ! prinrf( "902x ', *cprr++) ; if ( ( (i+1)*10) =- 0) printf("\D\r"); J // flee the nalloc'd free(srart_cpEr); nenory for ); next tine! J prinEf ('Faited to nalloc co.rectty.\n\r"); J I prinEf1 \n\rlteap size linit is gal\n\r', I{EAP_srzE_-4)' t Results:The USART transmits,at 9600baud, How nuch nenory should I fill?{ENTER) Then it waits until a number is entered followed by a newline character. Once this is received (15 for example), it transmits ehanks, I'11 try! Initial Values I 00 00 00 00 00 00 Modified 01 02 03 00 00 00 00 00 00 00 00 00 values ! 04 05 06 07 08 09 0a OB OC OD OE OF tnax #include <math.h> int max(int a, int b); '+?endi " .1-Librar! Fu"etians Refercnre signed char cma-r(signedchar a, signed char b); long lma;r(long a, long b); The zar tunction returns the maximum ofthe two integer values a arrd / as an integer. The tnatt, lnax, ndfnax trnctions return the maximum ofthe two signed char, long, and float values as a sigaed char, long, and float value, respectively Returns: Ma-rimum r-alue ofa and / sized according to the funaion called <nath.h> main ( ) +include void t int big inL,. signed char biq int = a char = b char = biq char a char, t' char, big max(1200, 3210),. //ger 23; 0x7A; = cmax(a char,b charl; char,. the naximM of the values vhiLe (1) t 1 Results: big big i n r = 32 1 0 cha! = 0x7A *mernccPy #include<string.h> For the TINY menory rnodel void *nenccpy(woial +dest, woid *src, char c, unsisned char woid *src, char c, unsiqned int n) ; For the SMALL memorymodel: void *nenccpyivoid *dest, n) ; The fnuton nenccpl copiesat most z bytes ftom the memory location pointed to by rr to the memory location lr until the character r is copied-The Är and sn memory blocks must not werlap. memcEyretrns a null pointer ifthe last charactercopied was e If r is not copied within the z bytes,then a pointer to the next location in l* (which is calculated asdst + n + 1) is retumed. 39s 396 Returns: Null pointer if r is copied to /s4 otherwise rctums l'l+z+1 +include <string-h> cha! inputstr [ ] ='S11.2+"; char ouEputstrl [6] ; char ouEputstr2 [6] ,' void I nain (void) a = nenccpy(oulputstr1,inputstr, b = nenccpy ( outputstr2 , inputstr, while .,3) ; . ,4); (1) { ) ) Results: o u t p u E s t r l = ' S1 1 ' a = outputstrl + 3 + 1 = &(outputstrll4]) ou!pu!6tr2 = "S11.' *memchr #include<string.h> For the TINY memory model: woid *nenchr(woid *buf, unsie'ned char c, unsiqned char unsigned char c, unsigned inl n); For the SMALL memorymodel void tt'uf, *nench!(voial n); Tl,e foactior' nemcltr searchesmemory starting at the location Pointed to by dfor the first occunence ofthe character r or until z bytes har.ebeen searched.Ifr is fouÄ Ä buf with\n z bytes, a pointer to r is returned. Ifr is not found, a null pointer is retr-rned. Returns: Pointer to the chancter cÄ tuf tf tis fotnd; otherwise NULL is rcturned +inctude <sLrinq.h> char lnpuLstr[ void nain{void) t ] = "$11.2#'; .1fie"dir )4 L;brzlt Fun.ria a = nenchr {lnpulstr, b = nenchr{inpuEsE!, vhile Ref.ftnr. '.',3); .,5),. (1) I ] ) Results: a = NuI,L b = &(inpurstr[3]) = ".2+' memcmP,memcmPl #include<string.h> For theTINY memorymodel: sisned sisned char char *tuf1, *buf1, woid *buf2, woial ftash unsisned char n); *buf2, unslgned char n) t *b,uf1, mencnp(void nencmpf (woid *bufl, woid *buf2, woid ftash unsisned int n); *buf2, unslsned int n); nencmp{void nencnpf(void For the SMALL memorymodel: sisned sisned char char The functions nenmp ^nd nerrlcn?fcompare the contents of the memory pointed to by ba|l to the memory polnted to by b P orcbyte at a time. The functions return aftff comparing two unequal bltes or after z bltes are compared,whichever comes 6rst. Returns: . siSnedchar < 0 if +buF,< *brrf2 . signedchar = 0 if *buf, = *buf2 . siSnedchar > 0 if *bufl > *buf2 +include <Etrinq.h> char inpulstr1[ cha! inputsEr2tl void nain (woid) ] = "nane b'; t sisned signed signed char char char a; b; c, 397 398 a = m e n c m p( i n p u t s L r l , i n p u t s r ! 2 , 5 ) ; b = nencnp ( inpulstr1, inputsEr2,6 ) ; c e m c m p la i r p u L s t ' l , a a m e I " , 6 ) : while (1) ) Results: c = 0x30 *memcpy, *memcpyf #include <string.h> For the TINY memory nodel .o d ,m-mcpy(void ,des., void rsr.i uns qacd trä. -), For the SMALL memorymodd: .o'd ,m-m.py{void 'dpsL, void.sr., unsigneo i-r n,j For eithermodelwhensrcis in FLASH: void 'mem.pyrrvoid *desL, void 's.., unsiqned in- nr j 'fhe fwctions nenEl and nenqyfcopy n bytes ftom the memory location pointed to by ,/. to th€ memory location point€d to by Äi For the funaion nenE , the .lst znd sn memory blocks must not overlap- This is not a concen \nrn\ nenE : becausethe sz. in flzerncfufmustbelocated in FI-ASH. Ifthe memory blocks do overlap, userzenmare irctezd of nemefu. Returns: Pointer to larr char outputstr[6]; char outputstrf[6]; void nain (woid) { a = nencpy(oucpursLr, inpuLsLr+l,4 ) ,. ourputsL![4] = \0 ; // nu11 Lerninate our new stlins Aff.,dix A-Libut! Furt,,a4, R./"4n b = nencpyf (outputstrf,'He11o worlal!',5) ; = '\o'r outputstrf[5] // nü11 terniDare our new stsrinsl ) ] Results: outputslr outpulst.f = 11.2 " = "He110' *memmove #include <stringh> For the TINY memory model: vo'o 'D-movF(voicl 'oesL, void +dest, woid src, unsiqned .l-d unsigned int ): For the SMALL memoryrnodel void hemowe(voial *src, n); The nenmose ttnctior copiesz bltes from the memorypointed to by srr to the memory pointed to by /eri Unlike nenry t}:'e're a d da$ nay overlapwhen callt'].gmemmove. Returns:/rst +incLude <strinq-h> char inputstrl void nain (woid) [] = "abc1'; one place to the right // nove the strinq a = nemowe {& (inputstrl [1] ) , inputstrl,3 ),. whire (1) { ) Results: 399 400 *memset #include<string.h> For the TINY memorymodel void *nenser(voial *buf, unsiqned char c, unsigned char n) ; unsiqned char inE For the SMALL rnemorymodd: woid *nenseE{void *buf, c, unsiqned n) ; The nensettutcnon Hls z bltes ofthe memorypointed to by r?rfwith the characterc Returns:,{,f +include <scring-h> char inputscrl void { [ ] ='abc1"; nain{voiaI) ,/ lill in vi-h so e 2's sLdrLinq dfte'd, 2,1) ; a = nenseE(&(iDpursErltll), while {1) t ] J Results: a = "222" inpütst.1 = 'a222' mtn #include <math.h' int min(int a, intb); signed char cmin(sisned char a, signed char b); long lmin(long a, long b); float fmin(float a, float b); The miz function returns the minimum ofthe two integer ralues a and / as an integer The fitnctions retorn the minimum ofthe two signed char, long, and float enin, lnin, adfnin values as a signed char,long, and float lalue, respectively. Äfie"dir.4 Libralr F"nctia"s Referen.e Returns: Minimum value ofa and / sized according to the function called <nath.h> +include woid nain{) { int littte sisned int; char a char, b char, littte_chart lirtte lnr = nin(1200, 3210); //c'et the niniftun of the values a char = 23; b char = 0x7a; iccle h-r c- a(--c'dr.b.här); while(1) { ] Results: inL = 1200 char = 23 Lirrle litrLe modt #indude <math.h> float modf(float x, foat \art); The zr4tunction splits the foating point numberu into its integer and fractional compo nents. The fiactional part of r is returned as a signed floating point number. The integer part is storcd as a floating point number at {azf Notice that the xddtess of the varinble to hold the integer portioo, not the variable itselq is passedto zouf Both the integer and the floating point results har"ethe sane sign as r Returns: . Fractional portionof the ffoadngpointnumberx asa siSned floatingpointnumber . Setsthe välueat the addresspointedto by *,psrato tie integer part of x #include <naLh,h> t !-oqt 'r!eqe -'-c'-poJlion jor. ion, lrä.1 moclr{ 45,7, porfionj !irtFoc,-po'rto )r &l 402 { J ' Results: integer_portsion = 45 peekb, peekw #include <mem.h> unsigned char pee!,b(unsignedint addr); unsigned int peekw(unsigned int addr); The peekn nctlon readsthe value ofSRÄM at the addtessadnr'lhe peeAu tunction reads an unsigned integer value from the SRAM at the addre:saddrThe peeAu tunction readsthe LSB 6rst fiom addressadlr arrd then reads the MSB of data kom addr+1. Values can be direcdy written to the SRAM by using the 7otuD rnd pokezof]ur'ctßI's. Returns:None Seepakeb,paAea for t\e code example. pokeb, pokew #include <mem.h> void pokeb(unsigned int addr, unsigned char data); void pokew(unsigned int addr, unsigned int data); ^llrLe The 2o,{e/ tunction writes the value of &rtl to the SRAM at the addressaddr. poke"n tunction writes the integer ralue oflrra to the SRAM ^tthe ^ddrcss addr.^ttß poAeu tunction writes the LSB of data frrst, to zd&ess addr and then writes the MSB of /ara to a1lr+7. Values can be read from the SRAM by uingrJrc peeAbandpeeAu ftnctionl Returns: None +include <nesa16.h> +include <nen- h> /* the strucEure alfa' unsiqned char b; unsigned int w, a l f a G0x260; ] is stored in s R A r i la t aalakess 260h */ A?fead;, A-L;b@rJ void F|ict;aß Refeteflce nain (woid) { unsiqneal int McUcR = 0xc0; read_w2; // enable = 0x11; = 0x2233; atfa.b alfa.w // // external ini.Lialize initiatize read b = (unsiqneal int) read w = peekw(0x261); pokeb(0x260.0xa4); pokew(0x261,0xBBcc); = {unsiqned = alfa.w; read_b2 read_w2 while // // // iDt) a1fa.b; J reaar_b = oxoo11 read_w = 0x2233 .ead-b2 = 0x00AA !ead_w2 = oxBBcc Pow <math.h> #include float pow(float x, foat y); TheTaa function calculatesx raised to the power ofy. *include { <nath.h> state the value at 0x260 the value at 0x261 place oxÄa at address 0x260 place oxcc ar addtess 0x261 and oxBB aL address 0x2662 (1) Returns: a./ l wai! peekl'{0x260); { 1 Results: SRÄM with 403 4u4 float new wa1; new vat = por(2,5); whi 1e(1) { ) ) new_val = 31.9 Results: POwerdown <sleep.h> #include void powerdown(voiQ; The 2ouerdownfonc:tronputs the AVR microcontrollerinto power-downmode.The funcnor., nee?-enable, must be calledprior to this function being used.In power-downmode, intemrptsandthe watchdog(ifenablea) the e*ernal oscillatoris stopped,while the ercternal continueoperating.Only an externalre.set, a rratchdogreset(ifenabled),or an externallevel interrupt canwakeup the MCU. Upon waking up from a;r intemrpt, the MCU executes the internrpt and then continuesexecutingat the instructionfolloraingthe sleepcommand Qanedbypozoerdown). Returns:None + inctude <meqra16.h> + include <sEdio.h> + include + include <s1eep-h> <delay-h> frequency /r quartsz crystal x t a l +define 6000000L /r Baud rate baud +define interrupl putsf void [Hz] */ t/ 9600 woid IEXT_INT1] ("I vas intl_isr (void) inEerrupted!\r"); nain (void) t POR|D - oxFFj DDRD = 0x00; // // pul- up on p. ) lurn on infernal p make rNTl {PoRTD ln 3) an inpuE Libturv F"n,t'oat R.Lp1 AP!.,dix 1 // Loü 1eve1 on INT1 inlerrupts // tuf,n on rNTl cIcR | =0x80 ' t iDterrupts MCUCR=0x00; MCUCSR=0x00; GIFR=0x80; /* initialize UBRRH=0x00; /* inirialize the IrSAR'I's the USART control no RX & TX enabled, */ rate baud reqisLer inter.upts, I dara bits */ UCSRC=0x86; +asn( 'sei"); sleep_enable( vhire ); / / eâble // enabte interruprs qro tso sleep us !o when {e are readv! (1) putsf ( "cood putsf('I Niqht ! \r" ) ; an qoinq co steep delay ns(100); poweidowno; // unlil you bus nel\r"); to be transmilEed! for strins // vai! until INT1 wakes us up enEer powerdom j Results: The microprccessor transmits Rese! Occuded Good Night ! I an going to sleep until you bus me! up only wher an INT1 interrupt occurs Theo it enterspowerdownsleepmodeand w-akes by PORTD pin 3 being held 1owor an extemalresetoccüs. Upon waldngup, it continues executingat the instructionfotlowing the powerdown.Upon wakingup, it will transmit the following continuouslywhile PORTD pin 3 is low: r was interrupted! The microprocessor continues to run the wh.ile loop until power is removed. POWerSave #include.sleep.h> &5 446 r.oidpowersave(-oid); The paarr.razafunction puts the A\.R m;crocontrollcrinto porversar.e mode.This is a sleep mode and very slm;lar to the pauenlau fonctron. Se. pa*dat t t t\is apuendlrfor rhe fur, rion us.. Seethc Atmcl datashcctsfor the completedescriptionofthis sleepmode rs it rpplies to a particular AVR device. Pol.ersave sleep mode is not available on all AVR devices. Prf i tttf #include <stdio.h> void print(char flash*fmtstr l, arg1,arg2,...l); Thepriailtunction transmits formatted text according to the lormat specitiets in theJntstr string. Thc transmittal is pcrlormed using the pzrr,4arfuncrion. The sta ,ald,putrhar lunc tjon delaultsto transmitting using thc USART. Horvever,it is possibleto usean alternate ?ut.har lnnction to red;rect thc data,.Scc?utüar for details. The nnplementationof2r;lls a reducedversionofthe standardC tunction.This las necessarydueto the specilicneedsofan embeddedsystemandbecausethe full implementation rvould requirer läJgeamount ofmemorl space.In ordcr to rcducecodc size,the usercan specif,vwhat options the Iri,rtis requircdto support lor their spccificapplication.Thcsc options can be acccsscdundcr thc ProjectlConfigurelC CompilerlCode Generatior (s)prindFeaturesoption. The format speci6erstringrr.,rrsrr is a constantand must be locatedin FLASH nemory and has the lollowing formrt: l tflaqsl tridthl t.precisio:l l1l Lype cha. The optionalr4agscharrcters are: Left justifiesthe result,padd'ngon the right with spaces.lfthisflag is not present,the result is right-iustified,paddedon the lefr with zeroes or sPaces. + Forcesa plus or minüssiSnto precededthe numericalvalue. (spacecharacter) A spacecharacterforces a spaceto precedea positivenumber lf the välueto be printed is negative,a minussign precedesthe value. The optional z,rZ,4 specifier sets the minimal uidth of an output value. If the result of the conversion is wider than the 6eld lvidth, the freld is erpanded to accommodate the result. Thc lollowing tr.dr.l specifiers are supported: n Forcesat leastn charact€rsto be outPut.Itthe result has lessthan n charäcters,thenits teld is paddedwith spaces.lfth€ flag is used, the resultfleld is paddedon the right,otherwiseit is paddedon the left. ,4f?.ndix 0n Ä Liblarr FLhLt;ah' Refefth.e Forcesat leastn charactersto be outDuclf the result hasfewer than fl chaiäcters.it is Daddedon tne bft witj' zeroes. The opircnal2recisian specifier sets the maximal number ofcharacters or minimal number 'f\e of integer digits that may be ouputted. pmision spedÄet alwaysbegins with a '.' in order to separateit fiom the oi4r9 specifer- The followingprecision speafiers are supported: .0 Setsthe precisionto I for üe 'i ,'d ,'u','x. and'X' rypechäracters. .n Forcesn (haractersor n decimalplac€sto be outFr. Specificallyfor the'i','d','u',Y,andX conversion typecharacters, if the valuehas fewer than n diSits,tien it is paddedon the leit with zeros.lf th€ value hasmore tnan n digits,then it will not be truncat€d.For th€ 's' and'p conversiontyp€ chamcters,no more than r charäctersfrom the string are out?utThe'e','E,andf' conversion typecharäcters areoutputwith n diSiBto the riglt oftne decimalpoinrThe precisionspecifierhasno efrecton tie'C conversiontype character. 1l no preÄ;an specrfiet is entered, the precision is set to 1 for the 'i', 'd', 'u, x', ard X' con'p' version qpe characters. For the t' and converstior type chrracteß, the char string is output up to the f,rst null chamcterThe optional'1' (lower case'I-) input siz,emodifer specifi€r thnt the tunction argument must be trexted as a long integer for the'i', d, u, x', and )C conversion gpe characters. The following conversion type chatacters,t5pecba,tare supported: c Outputs fie next argumemas anASCIIcharac€r d Outputs the next argumentas a decimalinteger i Outputs the next argumentas a decimalinteger u Outputs the next argumemas an ünsignedd€cimalinteger x Outputs the next argumentas an unsignedho<adecimalint€gerusing low€rca$ lefters X Out?utsthe nextargumentasan unsigned hexadecimal integerusing uDDercäse Etters e Outputs tie next argumentas a float formatt€d in scientificnotatior [-]d.ddddde[-]dd Outputs the nqt argumentas a float formatted in s€ientificnotation, [-]d.dddddE[-]dd Outputs the next arSumentas a float formatt€d as l-]ddd.ddddd OutpuB the next argumentas a null t€r"minatedcharacterstrin8 locatedin SRAM Outputs th€ next argumentasä null terminatedcharäcterstring, locat€din FTASH Outputstte%character 407 408 Returns:None +include <meqa16.h> +i n c l u d e < s E d i o . h > '| qud!Lz +define crysLat tlequency x!a1 ?3?2oooL /i Baud rate *define baud IHzl r/ */ 9500 nain (woid) void { unsisned cha. c; int j; */ /* initialize tshe USART's baud rare UBRRH=0x00; UBRRL=xral/16lbaud-1 ; .r iniLiai ze rl-e usaRT corrrol eqis!er Px & T'X anälrlFd, no inLerrupr s, I d-r- b ts UCSRÄ=0:00, UCSRB=0xD8, UCSRC=0x86, (j =0; j <=s00; j +=250) for Lhe cuftent walue of j // plinc printf ( Deciodl : gu\LHcxäde. imdl : g\\ n\'', j. j ) : printt("zFro P a d d e d D F ci m d | : g o u \ n \ r ' , j , ' plinlf ( "Four Digit Lower case Eexadecinal: *04x\r\n\n" ] while (1) { l/ Leceive Ehe chaldeter /' c=qeEchar O ; /* and echo it back */ printf character {"The leceiwed was $c\n\r",c) I ) Results: The following is ouput by the microprocessor to the USART at startup. Decinal: Hexialecinal: 0 0 zero Padded Decinal: 00000 Four Diqit Lowe. Case Hexadecinat: 0000 ; ,j I ; A?fddir Hexide.:m"l: Decimal: 250 P a d d e d D e c i n a l: 00250 zero Fou! Disit Decinal: zero Four tower sexidecinät: Libtzrt Ft"ttian' R FA Case Hexaalecinal: 500 I 00fa 1F4 00500 Padded Decinal: Diqit Loser Case HexaaleciGl: 01f4 Then any characterreceivedby the USART is rransmittedbackprecededby the specified süing. For exanple,if the charactert is received,this terctis sentto the transmitter. The received character vas z. putchaf #include <stdio.h> void putchar(char); The ?axtar Ä\ncrior' ß a standard C languageVO firnction, but it has been adapted to work on embedded microcontrollen with limited resources.The Tutchar fr,rlcttoa t^nsmits ^ character using the USARI This function usespolling to tmnsmit the character using the USART. As a result, the function waits indefnitely for a character to be transmitted before renrlnmg. Prior to this function being used, the USART must be initializcd, and the USART transmitter must be enabled. If another peripheral is to be used for transmitting, t\e puxbar firnctron cm be modified accordingl)r The soürcefor tiis function is in the stdio.h 6leIfyou want to replace the st lÄardlÄrlry ?uxharwith your own version, you must do three things. Fifst, you must place t\e new?ut Iff fnrction in the .r file before including the standard 1ibrary.Second,you must folow the newprralar function with a definition statement telling the compiler to ignore zlry oü,er patrtar fincrtons that it 6nds. Finally, include the standard library. Put together, the code might appear as (void) putchar void \our putcrdr rouLine ] , dEfiNE A-IERNATE +include <stdio.h> // Ehe rest of the PJTCHAR- source The st^ndaÄ?ut.har) rcturns:None + include <nega16.h> +include <srdio.h> file! släle-e^Ls he.- 4r0 /t quartsz crystsal frequency +define xlal 7l?2000L lHzl */ /* Baud rate */ +define baud 9600 void nain(void) { */ the UsART's baud rate /* initialize UBRRH=0x00; UBRRL=xral/16lbaud-1 ; the USART contsrol resistser /* initialize RX & Tx eadbl^d, ro inl-' rupts, I dd." UCSRA=0x00; UCSRB=0xD8; UCSRC=0x86; 0hi1e bi s (1) I the /* receiwe k=qerchar o ; /* and echo it putchar (k) ; character back */ */ t Results: Characters receir.edby the USART are echoed back ftom the USART until power is removed from the processor- Puts #include <stdio.h> void puts(char \tr); The 2zr function transmits the string srr using the stndaÄ puxhar function, or an alter nate?utchar tur'cnon tf one has been defned. The string must be nul1-terminated. A newline character is appended to the end ofthe string when it is trnsmitted. Finally, the string must be located in SRAM. (Seepz4ffor strings 1ocätedin FI-ASH.) The ?utehar ncnon defaults to transmiaing characten using the USART. Returns:None +include +include <neqa16. h> <6Edio.h> A?!."dix frequeocy crysla1 /* quarlz ?3?2000L +define atal Baud rate /* baud #define [Hz] Ä-Littat! Fnnt,iaa' R.I" "n,c */ */ 9600 char helto_str[] vöid nain (voiat) = "He110 World'; t the UsART's /* initialize UBRRH=0x00; UBRRL=ata1 /16lbaud-1, baud rate */ in: iälize Lhe USAPTconLrol reqiste' PX & Tx pnabled, no inlerrup.s, 8 dd!" UCSRA=0x00; UcsRB=0xD8; UCSRC=0x86; " puts ihetto vhile (1) I J Results: "Helo World", birs' str) ,. with line feed but not cafüage retrrrn, is transmitted using the USART. putsf #include<stdio.h> void puts(char flash ttr); The 2zrsrffunction transmits the contant stdng rf/ using the standardT*riar function, or an aTternateputchar frncaon if one has been defrred. The string must be null-terminated. A newline character is appended to the end ofthe stinA when it is transmitted. Finally, the 'lhe string must be located in FLASH. (See7* for strings located in RAM.) paxltar flnction defaults to transmitting charactersusing the USART. Returns:None +include <neqal6,h> +include <sldio.h> 'q-+define rz.rysrdl xtal Irequency 7372000L lHzl , 4tl 4t2 /'Baud #define race baud */ 9600 char flash hel1o void main (void) = str[] 'Eello the USART's /* lnitiatize UBRRH=0x00; r_tBRRL=xra1/16lL'aud-1; wo!1d"; baud rate */ /* initialize the USART conrrol leqisrei RX & TX enabled, no intserrupls, a daLa UCSRA=0x00; UCSRB=0xDa; UCSRC=0x86; bits */ pursf (he11o sL.) ; while (1) { ] J Results: "Hello World', with line feed but not carriag€ rctum, is transmitted USARII. rand #include<stdlib.h> int rand(void); The razl function retuns a pseudo-randomnumb€rbetween0 and 32767. Returns:None +include <neqa16.h> +include +include <stdio.h> <stdlib. h> 'oreriz #define this clysEa1 flequFn.y x!a1 73?2000L /* Baud rate +define baud void // */ 9600 main (void) to IPz] include '/ puEchar and printfl using the 4ffendi"4 */ /* initiatize the USART's Iraud rate UBRRH=OXO O; UBRRL=xra1/ 16/baud 1; /* initialize the USART control resisrer Rx & Tx enabled, no inlefuupts, a dara putsf("EnLer a seed value scanf("8d\n'.&seed); srand(seed); // seed the putsf("\n\rsedd while anythi4s to followed by L;b,ary F "ttiant Refere e '/ bits ENTER. "); seneraror get a pseualo-rddon Nrnbe!!\n\r'), (1) { qetcharO; // this will return rand nun = rand o ; .r( td\' \t ,ränd "-m), Pr w h e n S O M E T H I N Gi s received ) Results:The USART aansmits,at 9600baud, Enter a seed value folloveal by ENTER. Once a value is entered, the followiag is printed: Send anythinq to qeb a pseudo randon nunber! Upon the receipt of any character by the USAR], the next random number is transmitted. Notice that ifyou start with the same seed,you get the same number sequencecach time. reatloc #indude<stdlib.h> void *realloc(void .ptr, unsigned int size); 'fhe reallactunctiol changesthe size ofa memory bto& previously allocated in the heap by nalloc or olloc The size argument specfies the new size ofthe memory block. On succe"", the function retuns a pointer to the start ofthe newly allocated memory b1ock,the contents of which are a copy of the previously allocated block of memory. If the newly atlocated memory block is larger in size than the old one, the size difference is not fllled with zeros. The allocated memory block occupies size+4 bytes h the heap. This must be taken into äccount when specifying the heap size in the Project IConf,gure lC Compilerl Code Gener- 4t3 Retums:If successfirlin finding contiguous&eememorywith rize blres, returnsa pointer to the memoryblock- Ifrnsuccessfrrl retur-nsa null pointer. void main(vold) { : NULL; cpt. // = NULL; starE cptr initla),ize // // USART initiatization parmerers: cormunication // // // // USAR'I USART USART USART poinrers 8 Datä, Eo nutl! 1 srop, No pariry Receiver: On Transnitter: oD Moale: Asynch.onous Baud rate: 9600 UBRRL=xtal /16lt'aud-1 whire the ; (1) { putsf (' \n\rlrow nuctl nenory sttoutal r f ill ? (Er,rTER) \n\r " ) ; if (scanf("sd.,&nenory size) != -1) { if (nenory size < ( FtEAp_StzE - 4)) t printf ("\n\rl,hanks, t,11 try!\n\r,,); // if t.y Eo geL enough nenory (sEart cptr == NULL) 6ta!t cptr = maltoc(nenory size); slarl cptr = realloc (sEarr cprr,nenory cptr = sta.t_cptr; (cplr != NUIL) if { prinEf (.\n\rr4iria1 values: \n\., ) ; for (i=0, i<nenory size;i++) { printf *cptr size) ; ("S02x ",icpar);//prinr the inirial = (char)i + 1t // chanse the vaLue cptr++; // nove ( { {i+1) s10 ) == o) if Ehe pointe! vatue forwardl .4?fe"dir'1 L;brrry F ".tian' Referente pliocf('\o\r'); J prinrf ('\n\rModifieal values!\n\r") cptr = stari cptr; the new values! // print for (i=0; i<menory size; i++) { rhe nodifieal value! // print prinEf ( "*02x ". *cpE!++); if ( ( (i+1)810) -= 0) printf('\n\r'); ) ; ) ) t printf('\n\rHeap size 1i(it is gd\n\r", H E A Ps r z E - 4 ) ; ) l // if ve were going nenory here! // free{start cptr); on to alo other things we woü1d 'free' the ) Results:The USART transmits,at 9600baud, Then it waits until a number is enteredfollow€d by a newline characterOnce this is receir,ed(15, for example),it transmits Thanks, Initial I'11 tryl values I Modified vatues ! 01 02 03 04 05 06 0? 08 09 0a OB OC OD OE OF Note that the :r/s above represent the fact that these values are dependent upon what was preuously in the memory locationsallocatedusirg rcal/ae scanf <stdio.h> #include signed char scan(char flash 'fmtstr); 4ts 4t6 The srazlfunction inputs r,aluesfrom a text string according to the format speciiers in the ,4zrvr string and placesthe valuesin memory locations also specified by,4zfr: The fomat ting section ofther8rtrt string is enclosedin quotes and usesformat specifers, listed below, to tell rcd?twhat kinds ofvalues are to be read.Th e secoid p:ut of fmß/r Lsts the addresscs ofwhere the read values are to be stored. ATTENTION! It is imporrant to alwaysspeci8/ aI'o;nter .o thevarj^bte to receivethe value in thefutstr of the s nf tunction, zarthc variable itself. Failing to passpointers to the rca4f function causeserratic results, becausevalues are beine stored in the mimorv locations ,c lated to the r,alue of the variable passedinstead of bein! stored at the addrc* äftbe var;aore. The receiving of characten is performed using th e gexhar tuncioa.-lhe g,:tbal tunction defanlts to receiving using the USART Arr alternate sexbarfancion czibe deEnedto receive rh< darafron an alrernare Seegrrr,6arfor ditaiJ". "ource. The format specifier stringirzßrl is a constant and must be located in FLASH memorl The implementation ofsra4fis a reduced venion ofthe standard C thnction. This wäs necessarydue to the specifc needsofan embeddedsystem and becausethe firll implementation would require a large amount of memory The fo lowing formar specifersare avaiiable: %c Inputsthe next argumentas anASCll character %d Inputsthe nexr argumentas a decimalinteger %i Inpüts the nexr argument a5 a d€cimal integer %u hputr the noc argument as an unsigned decimal integer "/"x lnputs the next arSum€ntas än unsignedh€xädecimalinteg€r Inputsthe next argumenras a nullterminared charactersring Returns: Number of succcssirl entries or a -1 if an error occured +include <neqa16,h> +inc tude <stdio.h> /1 qua!tz crysiaL f.equency #define xraL 7372000L /r Baud rare a/ #define baud 9600 void main (void) { char your ini tial; you! nunber; int IHz] r/ t4?ô* t-"to,o,t the UsaRT's baud rate */ /* inltialize UBRRH=0x00; üBRRL=xta1/16lbauaI-1; the USARTcontrot register /* initialize T x I dara bits Rx & enableal, no inteffupts, üCSRA=0x00; UCSRB=0xD8; üCSRC=0x86; ,"n,rro"' .. r/ { Putsf('\n\t'); putsf('Ptease enLe. your firsE iDitial fö11osed by \r"); putsf('a coma then your faworite nunber.\r"); prtsf (.Pfess Ente. to finish, \r') ; // te1l scanf what to look for of the wariables are senr ro scanf! // NoTIcE the ADDRESSES ( s c a n f ( nunber) == 2) if Cc,3d\n',&your_initiä1,&yoür t _\". plintf("9c, co.qrdls! wou 9ol ä gdgg on you! exar your-initia1, Your-nuniber ) ; J pucsf('I didn'L undersldnd. Pleäse try aqain.\n r r: ] Results:The USART transmitsthc prompt for an initial and a number please initiat followed enter your first nunber. a coma then your faro.ite Press Enter to finish- by The $azlfunction waits for the initial" comma, number, änd newline character befor€ continuing. Ifthe user enters the following is printed: \n vour exd! If the user enters something Jike s, ac Then an enor occursand this is printed: I didn't unde.stand- Please try agrain. 418 srgn #include <math.h' signed char sign(int x); signed char aign(signed char x); signed char lsign (longx); signed char fsign (floatx); The r,g, function returns the sign ofrhe integer r. It retums -1 if the sign ofr is negative, 0 ifr is zero, or 1 if* is a positive value-The crzgz,/:ign, ar'dfsign fnlrctlons retuJn the sjgn of the signed char, long, and float variable r, respectir,.ebr Returns: . -l ifx is a negative value ' 0 ifx is zero . I if x is a positivevalu€ <nath- h> +include woid nain ( ) t - siqn{ neq siqn 195/41; pos sign lsiqr{1250001; zero sign - csiqn{0,j while (1) t J ) Results: --stn finclude <math.h> float sin(float x); t / /l // o. inEege! sqr Lh- s q "r _ons get t\sign o_ a or a c aL spr -hc siq A??.adix A-LibturJ F n.t;a,r Rertreße The ruz function calculatesthe sineofthe floating point number*. The anglerdis e{pressed in radians. Returns:sin(x) <nath -h> *include woid naino t ftoat.es new val wal, = sin{s-121); shlle { 1) { J I R€sults:new \d = {.918 s i nh #indude <math.h> float sinh(floatx); The siz,l Ärnctioncalculatesthe h)?erbolicsineofthe foating point number*. The angle;r is expressed in radians. Returns:sinh(x) +inctude void <nath-h> main( ) t float new wal, whi 1e ( 1) t I ] Results: new-val = 83.748 sleep_di$able #include <deep.h> void sle€p disable(void); 4t9 4m The slee?-dbable fnrlction clearsthe SE bit in the MCUCR register.This preventsth€ microcontrollerfiom accidentallyenteringsleepmode. Returns:None +incLude +ioclude +include +anclude /* quartz +define <neqa16.h> <6tdio-h> <61eep.h> <de1ay.h> crystat xral */ IHzl 6000000L */ /* Baud .ate baud +define inter.upt f.equency 9600 IExT INT1] void intl isr(woid) t putsf ( "I {as inEerrupEed!\r'); t nain (void) void PORTD = oxFF; DDRD - 0x00; // // pu11-up on pin3 EDrn oi internal nake IN1'1 (PORTD pin 3) an input MCUCR = 0x00; GIMSK = 0x80; // 1ow levet // tDra intefupt on INT1 ön ILIT1 inteüupts */ the USART'S baud rate /t initiatize UBRRII=0x00; UBRRL=xtä1/16lbaud-1, the USÄRT controt .eqister /t inltiatize Rx & Tx enableal, no lnteftupts, a dala bits */ UCSRB=0xD8; UCSRc=0x86; +asn{"sei"), // sleep_enäb1e0; // putsf vhile ( "Reser (1) enable enable occurred\r' inte.rupts go to us to sleep when we are ); t pursf { "Good NiqhE ! \r' ) ; puEsf('I an qoinq to sleep until you bus ne!\r"); readyl ,4??."dir,4 delay ns(100); idle(); // sreep disabteO; // ente. // LibturJ FLadioii ReJereh* sai-L for strins to be transnitted! idle until INT1 wakes us up stop future sleeps ) Results: The microprocessor transmits Reset Occurred cood Night I I you ouq nal Then it enters idle sleep mode and wakes up only when an tNTl interupt occurs by PORTD pin 3 being held low or an external reset occurs. Upon waling up, it continues executing at the instmction following the ir'la function. It transmits the following continu ously while PORTD pin 3 is held low: r qas intellupted! The next line disablesentering sleepmode- So, although the microprocessortries to call i//, to go to sleep,it does not. The microprocessor continuously prints the abovelines without a pauseuntil power is removed. sleep_enable #include <sleep.h> void sleep-enable(void); 'lhe neep_enabhtuncnon sets the SE bit in the MCUCR register. This bit must be set to allow the microcontr-oller to enter sleep mode when the SLEEP instruction is executed. When in sleep mode, some features ofthe microcontroller are stopped, allowing it to consume less power Depending on the t1pe ofsleep, the nicrocontroller can be awakenedby internal or external interupts. The particular deep nodes available depend upon the microcontroller being used. Refer to Aünel AVIR datasheetsfor the q.pes of sleep modes and their availabiliqr Returns:None *include <neqa16.h> +include <stdio. +include h> <sleep-h> +include <delay.h> +define /* xral 73?2000L Baud rate'/ +define baud 9600 421 4n nain (void) void { PoPTD - 0x04j DDRD = oxFB,. McucR = 0x00,. GIFR = 0x40,. /* iniliallze UBRRH=0x00; /* // turn // nake // 1os // turn pull on inLerndl uo o- p 12 ( P O R T D p i n rNTo 2) an inpul on INl'o 1ewe1 inEelrup! on INTo Ehe USART'S baud inEerrupts rate */ resister USART control n o i n t e r r u p t s , a data R* & Tx enabled, ioilialize the bits */ UCSRA=0x00; UCSRB=0xD8; UCSRC=0x86; +asn("sei"); // eiable sleep_enable(); // enable vhile interruprs us to qo to sleep when we are readyl (1) t pursf(.Good NighE ! " ); an going lo sleep putsf('I uotil rNTo wakes unEil // enEer idle was inLerruotedl ") : oisable(); // sLoo tuture sleeos idleo, pucst('I s-aap you bugr ne!")t us up ) Results: The microprocessor transmits Resei Occurred Good Nisht ! I an soins to steep untl1 you bug ne! Then it entersidle sleepmode and wakesup only when arr 1NT0 interupt occursby PORTD pin 2 being held low or an externalresetoccun. Upon waking up, it continu€s enecutingat the instructronfollowing the ile function. Upon waking up, it will transmir r was inEerrupted! The microprocessor continues to run the while loop until pover is removed. Ä.?endi. A-L;b,at! F,httiont ReJ'reift spi #include <spi.h' unsigned char spi(unsisned char data); Serial Peripheral Intcrface (SPI) allows high speed synchronous data transfer between de vices. Many ofthe Atmel A\.R dwices har.ehardware SPI ports. SPI ports allow data to be simultaneously transmitted and received orrr three connections: clock, master in slnve out (MISO), and master out slave in (MOSI). The master genentes the clock sipal and placesdata on the MOSI pin synchronized to the dock signal. The slaveplacesdata on the MISO Jjne, also slnchronized with the doclc In this way, data is transmitted and receil.ed bv both the master and the slaveat the same time. Once the SPI port is initialized, data transfer begins by placing data on the SPI data regi'ter ifthe microcontroller is the master Otherwise, thc microcontroller must wait for the clock from the master to transfer the data. A-lier the data transfer is complete, the SPI data register contains the value read f;om the other device. See the Atmel AVR datasheetsfor the requirements for initializing the SPI ponThe SPI tunctions are intended for easyinterfacing between C programs and rarious pe ripherals using the SPI bus. The tunction gi loads the SPI data register with thet'yte data, and then waits for the hardware to complete docking the data out and reading the data from the peripheral device. Once the transfer is complete, the gi firnction retums the data from the SPI data register Polling is used by gi to determine when the trarsfer is complete, so the SPI interrupts do not need to be enabled before this tunction is called. Returns: Character read from the SPI data register after the completion ofthe transfer +include <negal6. h> <de1ay.h> +include +include <spi.h> +include <stdlo.h> // This example reads +define xral votd ? 37 2 0 0 0 L main (void) { PORTA = PORTB = P0RTC = PORTD = oxFF; 0100; 0x00; 0x10; the shatus froh an Arnel 4T45D081 Ftash 423 424 DDRA = 0x03; DDRB = oxBF; DDRC = 0x03; DDRD = oxFF; // all // // all all inputs, except the lightsl outputs, except MrSO pinl inputs except for bit 0 and // all outputs '' Se id_ Pe iphctdl SPCR = 0x5E; SREG = 0x00; cll'4sx - 0x00; /* {/ serup intellupEs //Disat'te inlerrup //no extern"l s USART */ /* initialize UBRRH=0x00; /* irlerfä.F 1 iniEialize the register Ehe USART control no intetüpts. a dara RX & TX enabled, UCSR-4=0x00; UCSRB=0xDa; UCSRC=0x86, d-lä!_Fs{20001; PoRTD.4 = 0; delay-ns (s) ; ' ro seL slär // // wair püll the to! Ehings chlp .s send .omancl is returneat rhite // status senc // being spi (0x57) , = (int) stals spi (0x00) ; PoP D.4 - 1; printf ('scatus: */ USART'S baual rate rhe oe. to line sefeci r/ biEs srdb a low 0x57 0x00 second byte / /byLe the comand is r / /byt-e the chip // lelease sx\n\r',sEaEs) ; of serPc. 2 r in' whi le (1) I ] ] Results:The microprocessor transmits at 57600 baud on power-up Status: A0 sprintf #include<stdio-h> void sprintf(char*str,charflash.fmtstr [ , arg1,arg2,. . -]); The gn zffunction copiesthe formattedtext accordingto the format specifreß1nthefmßtr string to the string rti A null terminationis appendedto the end of rrr after the formafted .4p.adi,A L:::_::!:y:::::. texl is copied to it. The memory for rrr should be larg€ €nough to accommodatethe copied tex1 and the null termination. The format specifier string/r?trt is a constänt and must be located in FLASH memory. sP;n{ intetprets fntstr in the er<actsame manner ^s ?intfinterprcts fnßtr Seeprintffor more information on format specif,en. sqrt #include <math.h> float sqrt(float x); unsigned char isqrt(unsigned int x); unsigned int lsqrt (unsigned long x); The rqrr function returns, as a floating point variable, the squareroot ofthe positive floating point variable *. The isgrr and /.rgrufunctions retum the squareroot ofunsigned integer and unsigned long vaiables a respectively Notice the reduction in size from unsigned integer to unsigned char and from unsigned long to unsign€d integer in the irqrt and Ägd functions. Returns: r?/ - the squareroot ofthe positive floating point variable r ,rg,'r - the squareroot ofthe unsigned integer väriable :r as an unsigned char Ä4l- the square root of the unsigned long variable * as ar unsigaed integer +inctude <math-h> ftoat ny f sqrt; - _-_so t sq!tlb.4)j /t set t\p squä e 'oo! ot d f-oac my_l_sqrt = 1sq!t(250000),. // set the square roor of a lonq vatue = isqrr{41); ny_i_sqr! // get L}le square roor of an inr vatue I l ) Results: my_f_sqr! - 2.530 426 srand #include <stdlib.h> void srand(intseed); Thc srazl function setsthe seedr.alueusedby the pseudo random number generatorrazl Returns:None Scc mzlfor a codeexample. sscant #indude <stdio.h> signed char sscanf(cha;*str, char flash .fmtstr); The srary'function inputs r.aluesfrom the text string rrr located in SRA,\4, according to the format specifers in the1fizrsir string and placcs the values into memory locrtions also sp€c i6ed b,v.,r,zrs*The lormatting scction ofthej6,6t string is enclosedin quotes and usesformat speci6ers, listedbelorv,to tell srazlwhat kinds ofvaluesareto be read.The secondpart oflinrsa lists the addressesofrvhere the read values are to be stored. ATTENTION! It js important to als,ays spea$ a,pointer to the \ariablc to receive rhe valuein they4zirlrofthc rsca4ffunction,and zrtthe v3riableitseli Failing to passpointers to the $rdTy'functioncausescrratic rcsults,becausevaluesare being storedin the mcmorv locrtions relatedto the raluc ofthe variabiepassedinsteadofbeing storedrt the addrcssof the vadable. The format specifier string./zzrsr is a constant and must be locatcd in FLASH memory The implementation of sraz/is a reducedvcrsion ofthe standard C function. This was nec essarydueto the specifrcneedsofan embcddcds)'sternand becausethe lhll implementation rvould require a large amount of memory spacc. The lolJo"inglo,matrpe.'5e-'arearaiJablr anASCllcharacter %. Inputsthe nextärgumentas %d Inputsthe nextargumentasa decimalinteger %i Inputsthe nextargumentasa decimälinteger %u decimalinteSer Inputsthe nextargumentasan unsigned 7.x Inpursthe nextaEumentasan unsigned hexadecimal integer %s Inputsthe nexrargumenr asa null-terminat€d characterstring Returns:Numberofsuccesstulentriesor a l ifan error occurrcd +rnc lude <neqal6 - h> +include <stdio. h> ,+?endi' 1 crystal f.equency /* quartz +define xral 73?2oooL Liblar! Ftn.tia"t Rert/ehce */ [Hz] /* Baud f,ate */ +define baud 9600 cha! S O F T W A R Ev E R s I o l . I [ ] void main (void) = '3-5b'. { int najor_version; in! ninor version; char result6; /* initialize tshe USART's UBRRH=0x00; UBRRL=xral/16lbaud 1; baüd rate */ initiallze the USART co.lrot reqister Rx & Tx enabled, no intserrupts. a data UCSRA=0x00, UCSRB=0xD8, UCSRC=0x86, /* // // !eL1 sscanf what to look tor NOTICE Che ADDRESSESof Ehe variables lesulLs !f bits are */ senL = s s c a n f ( S o F T W A R E _ V E R S I O i i ," $ d . A d g c ' , & n a j o r &ninor ve.sion, &wersion_leEEer) ; to sscanft versior, != -1) (resutrs pri4lf("Major najo! version: version, gal, Minor Versioa Sd, Learer *c.\n\r nlnor_version, version lerrer) ; ) puLsf("An eftor while { occurred. soneEhing is nor riqhr!\r'), {1) J Results:The USART transmitsthe following: Majo! velsion: 3, Minor Version 5, LetEe! b. , 47 424 standby #include <sleep.h> void standby(void); The standb! fr\ncnon p'utsthe A\fR microcontroller into standby mode. This is a sleepmode ar.d simllar to the pouerdaoz function. Seepotuerdounin rhis appendixfor the tuncrion use. See the Atmel datasheetsfor the complete description ofthis sleep mode as it applies to a particülar A\.R device. Standby sleep mode is not available on all AVR devices. *strcat, :lstrcatf #include <string.h> char *strcat(char *str1, char "str2); *str1, *strcat(char char fash *str2); chnr The strmt and strea{ fur.ctions concatenate string srr2 onto the end of suing srr7. The memory allocated for rt must be long enough to accommodatethe new,longer string plus the nul-terminating character or else unexpectedresults occur. For the funcißn strcaf sft2 must point to a string located in FLASH. A pointer to srrT is retumed. Returns: *rt7 (a pointer to the null-terminated concatenation ofstrings rtrl and.str2) + i n c l u d e < m e q a 1 5- h > +include <sEdio.h> +inctude <sE!inq-h> /* qua!Ez +define frequency cry6tal 73 72 0 ool xral IHz] ,/ /* Baud rate t/ +define baud 9600 main (woid) void t char sEra t I = 'abc"; char sErbtlol; /* initialize the üSART's baud rate t/ UBRRr=xta1l16 /baud 1; r " i a l i z e r h e U S A R Tc o n r t o l t - s i s l ' r l D/ & TX endbled, no interr-p,s, I da-. bifs' A?fend;, A-L;tr'/r F"n.ti.ns Refeftn.e UCSRB=0xD8; UCSRC=0x86; strcpyf(strb, nxyz'); // initialize scrbt str.äL(sLrb,sr rd); srrcarf(srrb,'123" ); // ädd sLrd ro sLrb / / add a flash sEring root puts(strb), vhile (1) { // püt it out to tsbe USART'I ] Results:The USART transmits,at 9600baud, /,yzabc723 rtstrch r #include.string.h> char*strchr(char.str, charc); The rrzr,ärfunction locatesthe first occurenceofthe characterr in the string rr Ifthe char acterr is not found within the string,then a null pointer is returned. Returns:A pointer to the f,Jst occurrencecharacter. in string 14 if, is not found in srr a null pointer is returned +incLude +lncLude <nesa16. h> <stdio.h> *lnc1ude <strinq-h> flequency /* quarbz crystal +define xral ?3?2000L IHzl t/ /; Baud rate */ *define baud 9600 void nain (void) cha! st.a I I = "a2a.45"i char *strb; // no need ro a11ocatse space, poinLing // inro srra - already altocated! /* inilialize the üsART,s baud rare UBRRH=0x00; U B R R L = x E a/11 6 / b a u d - 1 ; */ 429 430 /t Ehe USART control no intedupis, Rx & Tx enabled, initialize regisler I data bits */ UCSRA=0x00,' UCSRB=0xD8,' UCSRc=0x86; -') ; strb = strchr(sEra,' gs\n\rNeo printf ( "Fu1t sErins: 's ,b / / t e p lä.e the ? ; in^. while srring': ts\n\r" , srla, slrb) poinl wi-h c ? decirdl gs\n\, ",si ro); ; (1) t ) Results:The USART transmits, ät 9600 bau4 Ful1 strinq: 123.45 N e ws t i i n g : . 4 5 Modified strinq: 123?45 strcmp, strcmpt #include <string.h> .str1, char *str2); signed chal strcmp(char *str2); signed char strcmpf(char *str1, char flash The nrcn? md strcn?f imctions compare süing strl w:nh sting str2. For the tunctron stcn?f üe str2 müst point to a string located in FIÄSH- The fuoctions start comParing with the 6rst character in each string. When the character in rtl fails to match the character in rrrZ the difference in the character values is used to determine the return value ofthe function. The retum value ofthe fuaction is the result ofthe subtraction ofthe ASCII code of th€ character from rt2 from tie ASCII code ofthe character from $r-t Retums: . negativevalueif str, < 5tt2 . zero if strl = str2 . positivevälueifstr, > sar2 +inctude <st.ing.h> char stiatI char strb I I sisned char sisned char = "seo.se ; = "seorsie"; resulE; resulEf; i4?.rdir woid A-L;brar! F i.tians Referenß nain (void) t iesult resultf = strcnp (stra, strb); rsreorqe ) = sElcnpf(stra, { J Results: result = oxFC ( e' - 'i' < 0) *strcpy, *strcpyf #include <string.h> char *strcpy(char *dest, char *src); char *strcplf(char *dest, char 0ash .src); 'lhe strcP! ^nd strc?fffunctions copy öe suing pointed to by vr to the location pointed to by lasL The null-terminating character ofthe r/r string is the 1astcharacter copied to the A$ string. The memory allocat€d for the /srt string must be large enough to hold the entire srr string plus the null-terminating character Returns: Pointer to lasr #include <nega16.h> +include <sEdio.h> #include <sEring.h> /* quarrz crystal frequency #define xral 73?2000L */ /i Baud rate +define baud 9600 void nain (void) = 'He11o ; char straII cha! strb[6]; char strc I6l ; [Hz] */ 431 437 the USART's baDal rate */ /* initiatize UBRRH=0i00; U B R R L = x r a 1 /1 6 l b a u d 1 ; reqlsrer Ehe USARI' control /* initialize I data biis Rx & Tx enabled, no interrupts, UCSRÄ-0x00; ucsRB=0xD8; UCSRC=0x86; strcpylsLrb,sl,äl; // copv sLr- s L! cpy I I s L r . , 'Lro I ld'); // copv puts (strb) puts (strc) ; ; // // transnit Elansnit */ ro s -b "b,o ld" Lo sf!c strl' strc (1) while t J ) Results:The USART transmits,at 9600baud, wortd The line feedbetweenthe lines is from calling thePuß fnr,cion. ?aß ^ppendsa line feedat the end ofthe string asit sendsit to the USART. strcspn, strcspnt #include <string.h> unsigned char strcspn(char *str, char *set); *str, char fash *set); unsigned char strcspnf(char 'lhe strcs?nand st es?nfÄtnctions retum the index ofthe fust character in the string rl/ th,r matches a character in the string ser-Ifnone ofthe charactersir the string $ris in the string rrt, the length of rt is reniJned.lf the first character in the string srr is in the stting tet, zerc is retumed. For the function fit?nf Äe stl:nrgsetmust be located in FLASH. _rn Returns:lndex ofthe first character ral rhat is in ff/ +include <6!rins.h> void nain (woid) { cha! char char char sertl = "1234567490-()"; ='1.800.555,1212'; stratl index-1; index-2; 4fe"di'.4 L;tralr Ftn.ti'ns Referen.e ndFr I sr '.spnlsLtq,sef)i index 2 = strcspnf(srra,.. O"); whire (1) J Results: index 1 = 0 strlen, strlenf #include<string.h> For the TINY memorymodel unsigned char strten(char tsErl; For the SMALL mernorymodel: . siqred 'aL sLrIen(chdr /sLr); For either memorymodd: unsigned lnt strlenf (cbar flash *str),. TEe urlen andst enfÄtnctionsreturn th€ length ofthe string rt; rot countingthe null terminator.For the ralez function with the TINY memorymodel in use,the length can be lrom 0 to 255.Ifthe SMALL memorymodelis in useandsrrlanis called,the length canbe from 0 to 65,535.The function srzlerfreturnsthe lengthof a string locatedin FLASH. Tnrs length canbe from 0 to 65,535regardlessofthe memorymodelin use. Returns:Length ofthe string sa +include void <strinq.h> nain (void) t char stra I I = "a2a4567A9O.; unsiqned unsisned char len1,. inE 1en2; 1en1 = strlen{slra); 1en2 = strfenf { 'abcde fqhij white J (1) klnnopqrstuwxyz,' ) ; 433 434 Results: Ienl = 10 Ien2 = 26 *strncat, *strncatt #indude <string.h> .str2, unsigned char n); char *strncat(char *s41, char clar +strocat(char *st1, char flash "str2, unsigned char n); T\e xrnnt atÄ *meaffunctrons concatenatea maximum of z charactersfrom string rt2 onto the end ofstring rtl. The memory allocated for srr1 must be long enough to accommodate the new,longer süing plus the null-teminating character or elseuner+ected tesults occur. For the function rtn ca6 !tr2 ro\tst poi'Jr b ^ string located in flash. A pointer to rlrT is returned. Returns: *r1,.7(a pointer to the null terminated concatenation ofstrings rt7 ,rld rlr2) +include <neqa16-h> +include <stdio-h> +include <strine'-h> crystal frequency /* quartz xtat 73?2oooL +defile [Hz] t/ /a Baud rare */ +define baud 9600 woid maln (woid) t cha! stra I I = "abc'; cha! strblsl; the UsaR'r's t'aud rare i/ /* iniriatize UBRRH=0x00; UBRRL=xral/15lbaud-1; Ehe USARTcontrol reqtster /* initialize '1Ler.uprs, I d.td Px & Tx enabled, no b: .s ' UcsRB=0xD8; UCSRC=0x86; stlcpyf (strb,'xyz" ); srrncat(strb,stra,2); sErncdl {sl b,'123',I); // iniEialize strb! // // add srra lo srlb ddd d I lasn scri o ool ,U|e"di" puts (strb) ; whl1e {1) { ] // pur 4 it Librzl)' Fr"üions Refercrre out to tshe usARTl Results:The USART transmits, at 9600 baud, strncmp, strncmpl #indude <stringh> signed char strncmp(char *str1, char *str2, unsigned char n); signed chr strcnmp(char *str1, char flash 'str2, unsigned cha.rn); 'fhe strnenp ard strncnpf functions compare at most z charactersfrom string rr7 to string rf2. For the tunction rrn .m6 stt2 mldisrpdl]lr @ a string located in FLASH. The tunctions start comparing with the 6rst character in each string. When the character in rr7 fails to match the character in rtz the difference in the character values is used to determine the return value ofthe inction. The retum value ofthe function is the result ofrh€ subtractiotr of the ASCII code of the character from rr2 from the ASCll code of the character ftom .rir7. Any differences between the strings beyond the z', character are ignored. Returns: . n€8ativ€ value'fstr, < st 2 . zero ifstrl = str2 . positivevalueifsr.l > str2 +include <srridg.h> void nain (void) { cha! cha! stra[] - iseorse slrblI = 'seorqie sisned resullf thile t J char ; iesul!; = strncnpf (1) ; (st.a, 'qeorge,,6); 435 436 Results: = 0 iesult :!strncpy, *strncpyt #include<string.h> char *strncpy(char *dest, char *src, unsigned char n); char \trncpy(char *dest, char flash '$c, unsigned char n); The $rnc?f ^nd strnEyftnnctions copy up to z charactersfiom the sfting pointed to by r,,. to the location pointed to by dest.Athere aliefewet thar z charactersin the r/. st(ing, then the r,., süing is copied to lerr and null terminating characters are appended until the total number of characters copled to dzrtis n.II $r sting is longer than or equal in length to z, then no terminating character is copied or appended.to d4st. Retuns: Pointer to dart #include #include <nega16. h> <stdio.h> #include <sLring.h> /t qualtz crystal frequeDcy *detine xral 73?2oooL /* Baud rare +define baud IHz] */ */ 9600 = "Het1oii, = "HELLo'. char char stra t I strb t i void nain (woid) 1 /* initialize the UsART,s baud rare */ UBRRL=X!a1 /16/baud-1 ; /* initialize the USART conElol register Rx & Tx enabled, no inrerlupLs, I dara strncpy(strb, sEra, 3) ; // copy stra birs r/ to strb 1?lendix,t strncpyf (sErc, 'irortal',10 ) ; // prlntf( "$s Cs\n\r., strb, strc ) ; Librz/r Ftn.tians Referen.e copy'irorld'ro srrc (1) while t J Results: Since':" is less than the total length of"stra", the 6lst tÄree letters are copied o!'er "strb", but no terminating null is copied- As a result, the originat ntrll termination is usedto teminate "strb"- So,the USART tränsmits,at 9600baud, *strpbrk, *strpbrkl #include <string.h> char \trpbrk(char *str, char *set); char 'strpbrkf(char *str char flash *set); 'fhe nrybrL and,strybrkfßtnctions searchthe string rrlfor the first occurence ofa character from the string rrt Ifthere is a match, the function returns a pointer to the character in the sojng J/x If therc is not a match, a null pointer is retumed. For the fun ci.on str?br4f, the string rcl must be located in FIÄSH. Returns: Point€r to the first chamcter in rrr that mrtches a character in rrl +include <heqal6 - h> +incLude <stdio.h> #include <string-h> /" quarlz crystat frequency #define xral ?3?2000L /* Baud raEe #define void baud [Ez] */ */ 9600 nain (void) I char srra t I - "11/25/O0"; char set[] char cnar char sr!b[] -pos; tfpos; = "/.,\'i = .Novenbe! 25, 2O0A"t 437 438 lhe usaRT's baud rate */ /* initiatlze UBRRE=0x00,' UBRRL=xtal/16/baud-1, t h e U S A R Tc o n E r o t r e g i s r e r /* initialize 8 data bits Rx & Tx enabled, no inEerrupts. UCSRÄ=0x00,' UCSRB=0xD8; UCSRC=0x86; r/ pos = slrpbrk{stra, seE) ; // find first // occullence of sonething l = ( s t r b , " , ') t sElpbrkf fpos ( printf Dale: 3s\n\r"srra); "foirial printf ("slringr followi4q natch: 8s\n\r",pos) ; printf ("ltust the yea!: *s\n\r',fpos+1); while (1) { I Results:The USART transmits,at 9600baud, Date: 1tl25l00 rni!ial maEch: /25l00 f o llowing string 2000 Just the year: strPos #include <süing.h> char stpos(char *str, char c); The srrposfunction locates the frst occurrenceofthe character rin the string rrr The index ofthe frrst occurrence ofr is retumed. Ifthe chancter r is not found within the strin& then -1 is returned. -l is Returns: Index of the flrst occurrence character . in string rtt if r is not found in srr +inelude +include <nee'a16.h> <stdio. h> +lncLude <string.h> frequeocy crysral /* quartz 73?2000L +define xtal /* Baud iate Iraud +define r/ 9600 IHzl */ ,4?fendk A-Litrrlr void F"n.tioas Referen.e nain (woid) char stra t i = "I7/25/2000"; char nonth_day,. char dayl'ear; /i initialize tshe UsART,s baud rare */ UBRRH=0x00; UBRRI=xra1/ 16/baud 1; /r initialize t h e I J S A R Tc o n t r o l regisrer RX & TX enabled, no interruptss, I dara bits UCSRA=0x00; UCSRB-0xD8; UcSRC-0x86; nonth-day = strpos(stra, day year = srrrpos(stra, prinEf ( ,sLartins /'); / ); Strinq: ( "Modified strins: while { ] (1) // find first slash characrer // fj,ad las.L slash characEer gs\n\r",sLra); // replace stash characrer . stralnonlh dayl = ' = '- ,, srra Iday-year] plintf */ sirh dashes Ss\n\rr,srra); ) Results:The USART trr.nsmits,xt 9600baud, Srarting Striaq: Modified stri4g: !1 /25/2OOO 11-25-2000 *strrchr #include <string.h> char .stnchr(char *str, char c); The yr7.r,, function locat€s the last occurrence of the character r in the string slx If the character . is not found within the string, then a mrll pointer is returned. Returns: Pointer to the 1ästoccurence ofchäracter c in stdng rr4 ifr is not found in rrl; a . , , 1 1- ^ i . r " ' i. .--,--, +include <nesa16.h> +include <stdio.h> +incLude <strinq.h> 439 440 flequency /* quartz crystal 7 3 7 2 o ooL x t a l +define IIiz] t/ /* Baud rare */ *define baud 9600 void nain (void) char stratI char *st!b; = "423-45 149"i // no need to altocate // inro stra - alteaily space, poancrnq allocatedl the USART's baud rate */ /' initialize UBRRE=0x00; TJBRRL=xra1/16lbaud 1; the USARTcontrol register /* initialize I data bits Rx & Tx enabled. no inierrupts, UCSRA=0x00; UCSRB=0xDa, U c s R C = 0 x 86 ; */ strb = strrchr(sEra, '. ); prinLf ("Fu11 strinlr: gs\n\rNev string: gs\n\!,stra,strb), 'strb = '6'; // replace rhe decinal point wlrh a printf ( "üoalified strinq: As\n\r', stra) ; shile t ] (1) ) Results:The USART transmits,at 9600baud, Fult strlng: !21.45.',l49 New String: .789 123. 456149 r{odif ied strinq: *strrpbrk' :tstrrpbrkf #include <sting.h> char *strpbrk(char \tr, char tet); .str, char flash.set); char \trpbrkf(char ^fhe sttrpbrA and *npbrkf tunctions search the string r// for the last occurrence of I charactei from the string ret Ifthere is a match, the function returns a pointer to the character in the string rti If there is not a match, a null pointer is returned. For the function strrPbrAl the süing set rrtustbe located irl FLASH. lpp.ndix A Lib,z,! Fnn,,rc1 .Al Rlpa"t. Returns: Pointer to the last character in sl/ thät matches a character in sar <neqa16.h> +include +inctude <stdio.h> *include <srrinq,h> ' q!ä.Lz +define crysläl frequ-n.y ?372000L xral /* Baud late +define baud void lHzl ./ */ 9600 nain (woid) I char strall char settl char char char strbll :pos; *fpos; = 71/25/o0" t =./.,1-"i = "Novenber inirialize the /i UBRRH=0x00; UBRRL=xrat /16lbaud 25, 2OOO"; USART,S baud rare r/ 1; inilialize the USART control register Rx & rx Fnäblcd, ro inLFrruprs, I ddrd UCSRA=0x00; UCSRB=0xD8; UCSRC=0x46; /* pos sLrrpb.l(sEro,selJ; // // fpos printf prinr ahile I ) II'sLr'1q tor-owing (1) ] strins in ll /25/OO | /00 follosinq match: strrPos #indude <string.h> chu strrpos(char *str, char c); , 2000 tuL.h: . aind lcst occurrence of sLr rpb' rt (srtb,',.-@g'); gs\n\.',pos); ( "Year in !!/25/O0: Results:The USAI{T transmits,at 9600baud, 'Iear bi.- ts\n\! ,rposr: sonethin- r 442 The rlnprr function locates the last occurence ofthe character c in the string szr The index of the last occurrence of c is returned. If the character r is not found within the string, then -1 is returned. Retuns: Index ofthe last occurrenceofcharacter r in string rrr; ifris not found in $a -1 rs retün€d +include <nesa16.h> +include <6tdio.h> +rnclude <strins.h> c.ystal frequency /i quartz 73?2000L +define xtal IHzl i/ */ /* Baud rate +define baud 9600 void nain(void) { cha{ srra t I ='La/25/2ooa"t cha! cha! monEh-day; day year; tshe USART'S baud /* inilialize UBRRH=0x00; /' */ rate the USART control iliEialize do intefupts, RX & TX enabled, regiscer 8 data biEs r/ UCSRC=0x86; -orth_ddy ddy_l,.dr printf - pos(sl .ä,'/ l; // r rpos(sr rä,'/ l i // sl s ( "sta.tinq strinq: slash characte. // replace stra fnonth_day] ='-', ='-'; stra lday-year] printf ('Modified while (1) ) ) scrinq: find tind gs\n\r",slra); {ith $s\n\r", dashes stra); fi,s! läs slosr -horä'r 6' ,4?feadi' A L;brdry Fun'tia,! Refeftnce Results:The USART transmits,at 9600baud, MÖdified Srring: 17-25-2OOO strspn, strspnl #include<s$ing.h> unsigned char strspn(char .str, char *s€t); unsigaed char strspnf(char *str, char flash .set); The sts?n ^nd, sts?nffiinctions retum the index ofthe fust character in the string rr that does not match a character in the string sa Ifall charactersin the string vrare in the string rer, the length ofrrr is retumed.Ifno charäctersio the string rrr are in the sting rcl, zero ß returned. For the functiorr stß?nf tIrc srring tet müst be located in FI-ASH. Rerurn<:Index ofthe first charrcrerin rt rhar is not inrd woid main {void) t chat setll = "123456?a90-O'; char straII = '1.800.555,1212", char index 1; char index 2; s t . s p n f ( s t r a , " , 1 2 3 4 5 6 ? 8 9 0 -O " ) ; while (1) { ) l Results: inilex 1= 1 *strstrr:lstrstrf #include <string.h> char *strstr(char *strl, char *str2); char *strstr(char +str1,char flash .str2); The strstr ^nd strstrffsnctions searchstring rtl for the 6rst occurrenceof s:.Jirlg$r2. Il str2 is found within trJ, then a pointer to the first cbrrr cllerof st/2 ln rtrl is returned. If rt2 is 443 444 not found in rt7, then a null is retufned. For the function frtl cated in FLASH. Returns: Pointer to +include +include +include tlre irst ch^r^cter of str2'tn $r1 or ^11 if str2 is not rn strl <neqa16.h> <stalio.h> <strinqr.h> frequency crystaf /i quartz xtat ?l?2000L *deiine [Hz] */ */ /t Baud rate baud +define void the stdng $,.2 must be 10- 9600 nain(woid) { cha! scrall cha! cha! cha! sErb t I iprr; iptlf, = "Red GreeD Bluei; = "Green"; tshe UsaRT's baud rate */ /* initialize UBRRH=0x00; U B R R L = x r a 1 /1 6 / b a u d 1 ; the USARTcontrol reqisler /* i,niEialize I dala b-.s Px 3 ox cndbled, no inlerruprs, // qrdb d poillar lo ahere creen is // srab a pointer to whele the filsE B is printf printf printf printf ('starting string: gs\n\r', slra) ; ('search string: gs\n\r', slrb); ( "Results string 1: Bs\n\r",ptr); ( "Results st.ing 2: Bs\n\r",ptlf); shl1e t ) (1) ,4?fcadi, A-L;brart F nttian' Ref.rena Resrnrs: T\e USART Lranqmirs. ar 9600baud, 9La!-tnq sL' ns: Red Grean alup Sealch sLring: Green Resutts string 1: creen Blue Results sLring 2: Blue *strtok #include <string.h> char *strtok(char *strl, char flash *str2); The function sfia,{ scans string rtJ for the f,rst token not contained in the string d/2 located in FI-ASH. The function expectsrrrT to consist ofa sequenceof tert tokens, separated by one or more chaJacteß from the string rrl2 (token s€parators).This function may be called repetitively to p?rse throqh a süing (f7) and retrieve tokens that are separated by knol{,n cha-ractersGr2). The 6rst call to *rol with a non-null pointer for rrl returns a pointer to th€ 6rst character ofthe 6rst token in srz7.The function searchesfor the end ofthe token and places a null termination character at the fust token separator (charaaer from srr2) following the token. Subsequent calls to r/rlri with a null passed for dr7 return the ner.t token from yr7 rn sequenceuntil no more tokens exist in srr7. When no more tokens ar€ fouod, a null rs Note that rtrrA modifies rtl by placing the nufl-termination characters after each token. To preserverlr7, make a copy ofit before calling rrrraÄ Returns: Pointer to the next token in.rrrT or null if no more tokens exist in rtt +inclüde <nesa16.h> +i n c l u d e < s t d i o . h > +include <strinq.h> frequency /* quartz crystat +define xral 73?2000L IHz] */ /* Baud rare */ +define baud 9600 cha! nyrexr I I = "1888)711-2222"t cha! flash separatorsll = 'O -'; void nain{void) { cbar area codel4l; char *p!efix; char *postfix; cha! backup copy[14]; 445 446 the USART's /* initiatize üBRRH=0x00; UBRRL=xra1/ 16 /t aud 1,. baud late */ initiatize the USART conrrol reqister RX & TX Fndbrad, no inrellupLs, 8 ddtd UCSRÄ=0x00,. UCSRB=oxD8,. UCSRC=0x86; /* // we wcnt Lo keep the o (backup,copy,nytext) st!cpy igindl d ourd b s ' ool ; to the area code // qrab a poinEer s-paral ots) ) i sL!cpy(dr ed_codP,s. r I ot (-yLcxr, // qtab a pointer p'ef ix - s,,lol(0, // to the prefix sepärälors)i a pointer srab to . the posrfix epararorsr; ("sldrl in9 slring: prinl es\n\r",bdckup p, inlrr'a Pd codF: gs\n\r"dred .ode): ('Prefix: printf Ss\n\r",prefix) ; gs\n\!',posr p-inl ! ('Posftix: Iix); ühi1e cooyr: (1) t I ) Results:The USART transmits, at 9600 baud, stariingr strins: laaa)771-2222 Area Code: Prefix:777 884 PosLfix.2222 tan #include <math.h> float tan(float x); The raa function calcul,ates the tangent ofthe floating point number x. The angle r is arpressedin radrans. Returns: tan(x) '!??.adh A +inctude void i Libr4rt Fq"ct;aks Refereße <mth-h> main ( ) float new_wal; new wal = tan{5-121); whi 1e ( 1) ) Re$Its: ne1v_val = -2.309 tanh #include<math.h> float tanh(floatx); The /rn,, irnction calculatesthe hyperbolictangentof the floating point numberrc The angle* is expressed in radiam. Reorns: tanh(x) +ioc1üde void <nath- h> main( ) I ftoat new_wal, new väl while - Länh{5.l2l), ( 1) t ] I Results: new_vd = 0.999 toascli #include<cqpe.h> unsigned char toascü(char c); The laarai firnction converts character r to a 7-bit ASCII format This is performed by the following defnition: *define toascii{c) (c) & 0x?f r'47 444 Returns: the ASCII value of r (valuesbetween 0 and 127) <ctype-h> #include void nain( ) { char ascii vatue,. = toascii ascll value ( 1 ) while (0x81) ; { J Results:ascii vrlue = (X31 ='1' toint #include <ct?e.h> unsigned char toint(char c); The lrizt function interprets the ASCII character r as a he"xadecimaldigit and returns an unsigned char from 0 to 15- Ifthe character is not a valid haudecimal digit, the tunction returns 0. Returns: Unsigned character ftom 0 to 15 representing ASCII character c + include <cEype-h> void nain ( ) hex_walue while {1) = toint('a' ) ; { ) Results: hex ralue = Orta tolower #include <cgpe.h> char tolower(char c); The a/atr.'erfunction converts the ASCII character dfiom an uppercasecharacter to a lowercasechamcter.If r is a lowercasecharacter,r is returned unchanged. Returns: ASCII character r as a lowercasecirracrcr + include <cEype.h> void () nai! 4??crdir.4 Lib ,r Fu,ct;an! Refercnce char tower_case_c; lower case_c = tolower('U'); vhile(1) t ) ] Results:lower-case c ='u' toupper #indude <cq?e.h> char toupper(char c); 'lhe to ??er fnfictroo converts the ASCII character r from a lowercase chasct€r to an ünpercasecharacter If r is an uppercasechafacter, c is retumed unchanged. Returns: ASCII character r as an uppercasecharacte.r <ct!.pe.h> nain ( ) *include void t upper_case_c = loupper { ,u,) ; while(1) { ) J Results: uoper case c ='IJ vPtftntf #include<stdio.h> void r,prind(charflash.fmtstr, va_list argptr); The e?rinffanc1jo'J ls identical to the function prhtf excnprew argjitr is a pointer to a va{iable{engthlist ofarguments-Thispointer is ofthe type a lit The 1)a_/tuq1e ts de fined in the header6le stdarg.h. Retums:None +include <nega16. h> the standa.d /* incLude <stdio.h> +include /* inctude che variabte <stdalar.h> #include +define +define xtal 6000000t baud 9600 input/output lensth tib.ary alsumeDL lists '/ nacros */ 1A9 450 /* 'o rourine lensth argüent list creaEe cuslon print wiEh a wariable fldsl_ '.p_fnLsLr, inl ddLd_lan, ...1 d cus!oml)r inL(.hdr va-1is! tolal /'totdl /* pointer cp-arsptr; = 0; l\e printf /* use wprintf (,'start of clear /t vä,idbl. custon to @iintf (cp_fntst., Lhe inleser to ä wariabte */ the talty or drgume.Ls r lensth aroüent lengl h drsumenl print out the cp argptr); values passed ro the walues rhe custon infornation about /* plint printf ('data len: sd\n\r',data 1en); printf (. rota1 value: Bal\n\r",torat); printf ('End of Cuscon Messaqe\n\!"); the dara cleanup va end(cp,arqpE!); void by ca1li.q Etle va function */ - end nacro our as inEeqers senr! i/ tso tserninate naio(void) // Paraneters: Comunication USART Receiwer: On USART Transnitier: On // usaRT Baud rarer // // */ r.fessage\n\rr); to reLurn /* now use the va arq nacio fo! { i=0; i<daca ten;i++) += va arg(cp !otal alqptr, inr) ; /* list a. po:n lisL I Data, 1 stop, No Parity 9600 UCSRB=0xD8; UBRRH:0x00,' UBRRL=xra1/16/baud-1 cusronjrinr("l4essage */ ; dara: sd gal gd gd gd sd\n\r",6,1,2,3,7,9,8); r/ ,41?end* Ä-Litrarr Fu"c/ia"! Refel.üe l Results:The USART transmits,at 9600baud, Messagedata:12379A Data 1en: 6 totat value: 30 End of Custon ltessage YsPrintf #include <stdio.h> void vsprintf(char .str, char flash *fmtstr, va-list argptr); The vsprintf flJJJcoonperforms almost exacdy ^s ltp;n{ peÄor'r,]'s,exc.pt th^t u?inf copies the formatted text according to the format spect6eßn thefntstr string to rhe strnrg rtz instead ofto the USART- A null termination is appendedto the end ofrrr after the formatted tert is copied to it. The memory for rrr should be large enough to accommodate rhe copied tet and the nul1 termination. Seepinffor more inlormation on format specifiers ar.d uprin{for a cnde exanple. 451 Getting Started with CodeVisionAVR and the STK500 FEATURES . Inställin8 andconf8uringCodevisionAvR to workwith theAtmelSTK500 starter kit andAVR Studiodebugger: . Creatinga new projed usingthe CodewizardAvRAutomatic Program Genemtor . EditingandcompilingtheC code . Loadingrhe executablecode into tie target microcontroller on the STK500 starterkiL INTRODUCTION The purpose of this document is to guide the user tluough the preparatron of an crample C program using the CodeVisionÄVR C compiler The example, which is the subject ofthis application note, is a simple program for the Atmel 4T9058515 microcontroller on the STK500 starter kit. PREPARATION Install the CodeVisionAVR C Compiler by executing the file setup.exe. It is assumedthat the program was installed in the default directory: C:\cvart. Install the Atmel AVR Studio debuger by execlting the 6le setup.exe. It is assumedthat AVR Studio was instäled in the default directory: C:\Program Files\AtmeNAVR Sirdio. The demonstration program to be dercloped in the nert few pagesrequircs an Atmel 4T9058515 microcontroller and the STK500 starter kit. Set up the starter kit according to the instructions in the STK500 User Guide. (Retnhtedca"rtet af Ptut Haidu nd HP I"faT..n s.R.L.) 453 454 Make sure the power is o{f and insert the AT90S8515 chip into the appropriatesocket marked SCKT3000D3. Set the XIAL1 jumper. Also set the OSCSEL jumper betweenpins 7 and2. Connect one 10 pin ribbon cablebetweenthe PORTB and LEDS headers. This will allow displayingthe stateof 4I90S8515's PORTB outputs. Connect one 6 pin ribbon cablebetweenthe ISP6PIN and SPROG3 headers. This will allow CodeVisionAVR to automatically program the AVR chip after a successful compilation. In order to usethis feature,one supplementarysetting must be done: Open the CodeVisionAVR IDE and selectthe SettingslProgrammer menu option. The following dialog window will open: Make sure to selectthe Atmel STK500 AVR Chip ProgrammerType and the coresponding Communication Port, which is usedwith the STK500 starterkit. Then press the STK5OO.EXE Directory button in order to speci$rthe location of the stk5O0.execommand line utility suppliedwith AVR Studio. (Reprinted tourtesyaf Pavel Haiduc and HP lxfoTech S,R.L.) Appendi* B-Getting Starteduitb CodevisioxAYRand tbe S'1K500 The following dialog window will open: ACDSyBtBm$ Adobe AdobeType Manaqef Alloy AppletButtonFactory Almel Select the C:\Program Files\Atmel\AVR button. Studio\STK5O0 directory and press the OK Then pressthe OKbutton once againin order to savethe Ptogrammer Settings' In order to be able to invoke the AVR Studio debugger/simulatorfrom within the codeVisionA\rR IDE, one final setting must be done' Select the Settings lDebugger menu option. The following dialog window will open: Enter C:\Pro$am Files\Atmel\AvR Studio\AvrStudio.exeand pressthe OK button' (Re?rintedcourtes!ofPaoelHaiducaxdHP lnfoTbcbS.R.L.) 455 456 CREATING A NEW PROIECT In orderto createa newproject,selectthe FilelNew menuoptionor pressthe lfifl toolbar button. The following window will be displayed: SelectProject and pressOK Then the following window will be displayed PressYes to use the CodeWizardA\rR Automatic Prosram Generator. (Rz?inted coartes!of Pooelllaidac andHP InfoTbcltS.R.L-) Appendix B-Gett;ng Staüed 1!;th CodeVisionAVR and the STK500 USING THE CODEWIZARDAVR AUTOMATIC PROGRAM GENERATOR The CodeWizardAVR simplifies the task of writing start-up code for different AVR microcontrollers. The abovewindow opensand, for this exampleproject,we shall selectthe 419058515 microcontroller andsetthe clockrateto 3.68MHz sincethat is the clockon the STK500 starterkit. (Re1rintedcourasyof PavelHaiducandHP InfoTechS.R.L.) 457 458 CONFIGURING THE INPUT'OUTPUT PORTS Selectthe Portstab to determinehow the I/O portsareto beinitialized for the targetsystem. The default setting is to have the ports for all the target systemsto be inputs (Data Direction bits to be all I's) in their Tü-state mode. For this exercise,we want to set Port B (by selecting the Port B tab) to be all outputs and we do this by setting all the Data Direction bits to O (by clicking on them). We also set the Ouqrut Values to be all 1t since this coresponds to the LED's on the STK500 being off CONFIGURING TIMER I For this project,we want to configure Timer 1 to generate overfowinterrupts. (ReprinxdcourteryafPavelHaiducandHP InfoTbchS.R.L.) ,4??endi,. B-Getting Started,Ttith CadeVitionAVR and the STKSOO We select the Timers tab and then select the Timer 1 tab resultinE in the window shol,qn below. Set the options asshown in the abovewindow We haveselecteda clockrute of 3.594 kJfz (the systemclock of 3.68 MHz divided by 1024). The timer is set to operate in the default "Output Compare" mode and to generate interrupts on overfow. To obtain the fiequency of LED movement of 2 per second we need to reinitialize the Timer 1 valueto Ox10000-(3594l2)=OxF8FB on everyoverfow. (Reprinted nartety ofPavel Haiduc and HP InfoTbcb S.R.L.) 459 460 coMPLETTNG THE PROIECT By selectingthe FilelGenerate, Saveand Exit menu option the Code Wizard will generate a skeletonC program with, in this case,the Port B and Timer 1 overflow interrupt set up correctly. The following dialog window will appear: By pressingthe El button, a new directory C:\cvaw\led wi11becreated. It will hold all the files of our sample project. Then we must specifythe File name ofthe C sourcefile: led.c and pressthe Savebutton. A new dialog window will open: (Reprinndcourtesy af PaoelHaiducandHP InfoTbchS.R.L.) ÄP?e di)c B-GettitTg Started u;th CadeVisionAVR and the STK500 Here, we must speci$/the File name led.prj as the project name and put it in the same folder: C:\cvarr'\led. Finally, we will be prompted to savethe CodeWizard project file: We must speci$.the File name as:led.cwp and pressthe Savebutton. Saving all the CodeWizardAVR peripheral configuration in the led.cwp project file will allow us to reusesomeofour initialization codein future projects. The led.c sourcefile is now automaticallyopenedand available.One can then start editing the codeproducedby the CodeWizardAVR. The sourcelisting is given on Appendix A of this applicationnote. In this example,only the interrupt handler codeneedsto be amendedto managethe LED orsPray. The smallbit ofcode which was addedis shownhighlighted; the remainderwas suppliedby the CodeWizardAVR. v l E w t N G o R M O D t F y t N G T H E P R O I E C TC O N F t c U R A T t O N At any time, a project configuration may be changedusing the ProjectlConfigure menu option or by pressingthe ffi toolbar button. (Refrintednurtesyof Paul HaiducandHP Infinth S.R.L.) 461 462 The following dialog window v/ill open: To add or remove 61esfrom the project, select the Files tab and use the Add or Remove buttons. To change the target microcontroller, the clock rate, or the various compiler options select the C Compiler tab. The following window opens and the configuration may be altered: (Re?lintedcoürtes!afPaoelHaiducandHP InfoTecbS.R.L.) A??endie B-Getting Started zoith Cadel/isionAtR and the STK500 We may also select \irhether we wish to automatically program the target microprocessor after the Make or not. This is chosen by selecting the A.fter Make tab, which gives us the next window. For the purposes ofthis example, the Program the Chip option must be checked. This will enable automatic programming of the AVR chip after the Make is complete. MAKTNG THE PROIECT The Project pull-down menu gives the Make option. Click on it or on the lP the toolbar. brrtton ort After a successfirlcompile and assembly, the Information window will be displayed as shown below. (Rzprixtedcourtesy ofPavelHaiducandHP InfoTuh S.R.L.) 463 464 Chip:4T90SS515 model:Srnall lor Size chnrloint No isunsigned.Yes #define:Yes On €gis€r allocadon: UseAVRStudioTerminelUO:No '1 88 line(s)compiled Erorg u,ffnings 6izErBbyb(6) 51ACKere8: bUnrO Uin Stacksize:,|20hde(6) Globolvaiebless zer0byte(s) 25Fh Stacke€a:Eohlo StdckBize:384 bde(s) This window shows how the RAM memory was used by the compiler. (Rc?rintedcourtes!tPaoel HaiducandHP InfoTbchS.R.L.) Äppendix B-Gett;ng Started @;tl CodeVisionAVR and the STK,00 If the Assembler tab is clicked, the Assembler window shows the size of the assembled code,asshown below Selecting the Programmer tab displays the value ofthe Chip Programming Counter. This counter can be initialized by pressingthe Set Counter button. (Refrintedcourtesy af PavelHaiducaadHP InfoTethS.R.L.) 465 lf the X4ake proccss was successtul,then power up the STK500 st tcr kit and press the Program buttun to sLr.r tl-e automaticcJripprogramming. Alter the progranming processis complete, thc codc will start to execute in the rarget mi crocontrolleron the STK500 starterkit. SHORT REFERENCE Preparations: l. InställtheCodevisionAvR C €ompiler 2. lnställtheAtmelAVRStudiodebugSer 3. lnstallthe AtmelSTK500starterkit IDEby selecting: 4. Confgureth€ STK500progrämmer suppon'n the CodevisionAvR Settinge>Prog.ammer-> AVRChipProg.ämmerType STK500-> Directory:C:\PrognmFiles\Atmel\AVR Studio\STK500-> Specify STK500.E,(E Communication Pon theAVRStudiosupponin the CodevisionAvR IDEby selecring: 5. Conngure Seftings->Debugger-> Enter:ClProgramFjles\Atmel\AvR Südio Gcftiflg Stä.rted: | . Creätea new proiectby selecting: Project File->New->Select will be usedfor producing the C sourceandproiect 2. Sp€ciry that the CodewizardAvR fil€s:Usethe Codewizard?->Yes windowspeciry the chiptypeandclockfrequency: 3. In the CodewiuardAvR | 5->Clock3.86MHz Chip->Chip:4T90S85 4. ConflSure the l/O pons:Pons->PortB->DataDirection:all Outputs->Outputvalue. ä l lI s l->ClockValue:3.594kHz-> Interrupton:TimerI 5. ConfigureTimerliTimers->Timer Overflow->Val: 0xF8FB 6. Generatethe C source,C pro,e€t, andCodewizardAvRprojectfllesby selecting: FilelGenerate, SaveandExit-> CreatenewdirectoryiC:\cvayr\l€d-> led.cwp Säve: led.c->Save: led.prj->Säve: 7. Editthe C sourcecode (Refl;ite,t t.nrks).tPad Haiduc aad HP InfaT.rh S.R.L.) Slarted {itl A??erdi. R-G.tti,g Codevitio'AI'R and the STK5AA L View or modit the Proiect configuntion q/ selectingProiect->Confr8ure-> After Mäke->Programthe ChiP 9. Compilethe programby selecting proSramtneAT90S85l5chiPon the STK500stanerkit: 10. Automaticälly Apply power->lnformation->Progräm- T H E S O U R C EC O D E This piogran was Ploduced L'Y Lhe coder'ilzardAvR v1- 0 . 1. 8c stanalard Autönatic !rosran Generator O CopyiierhE1998-2001 ö-l.t s.R.L P In.o6c.h r o i ! . i n f o t e c h . / / ro, hpinfo hpinfoLech@xnet. e-nail: nd.Ldu-, http: rype cLock frequency Menoly nodel External Data +include : 3.680000 uHz : Sna11 SRAM size : 512 SRAM size : 0 : 124 size Stack <90s8515. h> be // the r.ED 0 oD PoRTB wtIl leal 5tatu6=o*FEt unslgDeal char // Timer in!errupt l oü rourine service intelrupt t i n e r l o v f i s r ( void) v o i a l lT1141-ovFl overflow I D- . ro : 4T90S8515 chip Inlernal cechenail n;ti"_ 2. rime 's | !dlue TCNTlH=OxF8; TCNTlL=OxFB; // Place your code here (RePiatNd Mts' d Paut Haidx. a"d HP hIaTb.n S.R:L) 467 464 tl!6 r.ED / / rcw. 1ed_alatua< <-1i (16t1 statqs==oaFF) tun oD tlle lED // PORTB!loal atatust if ledl_3tatüa.0xFE, ) woid nain(woid) t // hpur/ouiput Ports initializalron DDRB=0xFF, DDRC=0x00; DDRD=0x00; // Tinei/CounEer 0 initialization // clock source: Sy6ten Clock 0 Stoppeal // Clock value: finer // Mode: Output Conpa.e // oco outpur: Disconnecteil TccR0=0x00; TCNT0=0x00; // /,/ // // // // // // Tiner/Counter 1 initialization Clock soulce: Systen Clock clock walue: 3.594 kEz Mode: Outpul Conpare oclA oulpuE: DisconDiscon. oClB oulput: Noise CaDceler: off on Falling Edge rnpul capture (Brpi'ad .otrt6t ofPtut ru;dü df,dHP hfoTdt S.R.L) 4f?e,di' B-Geltina Sto,t.d tuitb Coder.k;o',4r.R 'nd rhe STK50O TCCRlB=0x05; TCNTlH=0xF8; TCNTlL=0xFB; ocRlAH=0x00; ocRlAL=0x00; ocRlBH=0x00; ocRlBL=0x00; // External // INTO: off Interrupt (s) initializaEron // INT1: Off CIMSK=0x0 0; MCUCR=0x00; // Tiner(s)/counter(s) TIMSK=0x80, hterrupt{s) // Anatog conpa.ator i4iEialization // // Anatog Analog conparator: Conparator off Inpu! // Globat enat'1e inter.upts // tbe is b!' lest ato!€ |Ilttlil Captüre iaitialization by Tine!/CounLer overfloe int€ralrrE ) ß4nnd @t , of P4wt Haidü andHP l"faTe.n s.F L) 1: Off 469 Programming the AVR Microcontrollers The purpose of this appendix is to introduce thc rarious programming methods available and to provide enough information to troubleshoot programming prob lems. The information given is not intended to bc suflicient to ernble the rexder to create a programming device; see the microcontroller specification if you wish to cfeate your own Programmer ,AlI microcontrollers (and microcomputers of all tvpes) rcquire that all or part of the operating program be resident in the computer when it starts up. trlticrocontrollcrs and computers cannot do'hothing" (i-e., they must be er<ecutingcode at all timcs when they are mnning). If they are in a "do-nothingz loop, they may be accomplish ing nothing, but they are still executing the code that makes up the idle loop. This means that the operating codc must be permanently storcd in a non-volatile scction ofmemory In the caseofthe Atmel A\tR microcontrollers, this memory is conposed of flash nemory. And, assuming that you are not using an in-circuit emulator or a simulator the code must be programmed into the flash memory in order for the code to be run. Atmel provides on board programrning via the SPI port arrd via a parallel program ming scheme.The SPI nethod is actually used almost exclusivelyto program the devices.The program bltes are applied to the SPI port in a specific sequenceand are subsequendystored into the flash memory This code is thcn cxecuted the next time dre microcontroller is reset.Thc huge advantageto SPI programming is that it a1most alwayscan be done in circuit the devicesdo not nced to be removed fiom their application and programmed in a special prograrnming device. This allows for easy lield uDsradesin the cornmercial world. 471 472 SPI PORT PROGRA]'IMING As an example, consider the method of programming an 419058535, which is as follows: RESET andSCLKlow for is power€dup andrunning,hold l. Aft€r the micro€ontroller at least20 ms. 2. Sendr}.e Pngonning Enoblecommandword into the microcontroller via the SPI poft. Duringthe transmission of the 3d byte,0x53shouldbe echoedbackto the Proa dummy4- blte gramming device.Finishthe commandby sending 3. Transmitthe write P.ograr,/t4ernorycommandcontäinint the addressof the byte to be written andthe byte its€lf (seeFigureC.l below). to pollthe bytejustsenrReadbackthe 4. Usethe ReadPrograml4emorycommand into (0xff will b€ sent backuntilthe byteis programmed byt€untilthe byteis corect the flashmemorY). 5. Repeatsteps3 and4 untilthe entireprogramcodeis loadedinto the flashm€mory 6. S€tRESET highto resumenormaloperätionandto executeth€ codenow loadedinto the microcontroller Nate:AI af the?,agram,'ing annand bytesreqaneüe transnision af4 brtes ta the m1ffoe1ntroler teing ?rogranne.l Alfaar nust aluars be transmittedfor synchranization?aryosd eten thaughlone nar bedunry bttes. Other operations may be executedon an -A19058535 in a manner similar to the above by the selection ofthe appropriate command word from Figure C.1. The actual SPI programming commands vary somewhat among the various Atmel AVR microcontrollers. Check the specification for your particular device for details. COHMERCIAL PROGRAMMERS There are a number of commercial programmen available to allow progamming the fl:sh code memory of the microcontrollers. Some, such asTheCableAVR made by Progressive Resources,LLC, use serial or USB communication to the PC. These gpically use an Intel HEX file as their source for the code. These units have soohisticated PC softlvare to control the programming processand include features such aJautomatic erase/program/vcrifr sequencing. They also have additional electronics to convett the serial inJörmation into SPl-compatible conmunication. A number olother devicesalso usePC software to program the microcontrollers, but they do so via the PC parallel port. These mosdy manipulate the bits ofthe parallel port to simulate the action of the SPI bus in communicating with the microcontrollers. Devices made by Kanda Sptems (STK 200+/300), Vogel Electronik (VTEK-ISP), and the programmer built into the Atmel STK500 development board are ofthis gpe. These latter programmers are also supported direcdy by CodeVisionAVR so that thc microcontrollers may be Programme.i from within the CAVR IDE. These devicesgpically are somewhat slower and less sophisticated in their approach and flexibility than the serial device described above. Byte I A??endir C-Proglaflni"g B,fte 2 Byte 3 tb. '1t'R M;tlatanttaleß Byte 1 1010110001010011 01010011 Nlode Send 10101100 Chip Erase EEPROI,l Scnd 00101000 Mcmory High Byte Menory-High Rmd High Brte from Rd. 00100000 ReadLow Brte fron Plogiam Menory word SenJ 01001000 Writc High Bltc to Progrm Memory lvord Blte Send 01000000 Nlenorr-LN Bfe RcadEEPRONI 10100000 ReadEEPROT\I Nlemory Blte at 11000000 Write EEPRONI MemoryBlte at Rd. Write EEPROM Rd. Notesr 1. a = addressbit b = databit x = don't cre bit 2. There are also comnaods to poll and rrite the lock bits. See pan specification for detalls. 'Chip 3. Erase" requires a RESET and new "Progranming Enable" after the erase is succesArl. Fisure C-f 419058535 SPIPtogrcmmineConnond wotds 473 BOOT LOADER PROGRAMMING Some of the Atmel devices,such as the AIMega16, also allow for selfprogramming via a baot loada progrzn.-lhese devices are capable of writing data to the flash code mcmory under the control ofan on board program called a baolloader. The boot loaderprogrammust be lrdtten and storedin the bootloadersectionoffläsh code memory This scction of menory is protected from orenvriting by setting the xpProPriate lockbits. The advantageto a boot loadcr program is that it can be tailored to the applicntion; i.e , if you want to be able to upd:tc the llash code memory from the serial port, then rhe boot loadcr can be rvritten to accept datx serialy (formatted in some standard form such rs an Intel HEX formatted 6le, for instancc) and the data placed into flash memory To usea bootloadet theloader program nust be programmed into the upper section offlash memory, called the /aol loader:exion. Contolbits are thcn set so that a RESET causesthe bootlldder ro stutrwatching the chosen input device (i.e., the serial port). A certain string of characters,followed by the program code, kels the boot loader to start re-programming the flashsectionofthe dcr.ice.Receiptofthe rvrong string ofcharactersor the passagcofa set amount of time without recelpt of the conhol string rvill causethe boot loader to transfer control to the beginning offlash code memory to executethe stored ProgramThe ad\antage to a boot loader program is that it allorvs field reprogramming lrom almost any device wanted by tailoring the input device to suit the needs.For instance, some devices use the serial port and may be entnely reprogrammed by a PDA such as r Palm Pilot. Installing and Using TheCableAVR SYSTEM OVERVIEW ThcCableAVR is a tool designcd to serialh progrxrn thc Atmel ln-Svstem Pro grammablemicrocontrollers.It consistsof a Windorvs@applicntionand a spccixl downloading cable. Bv ut;lizing the specialized hardrvare in the downloading cablc, the PC applicationa1lowsthe userto read,program,and rerifi manr.ofthc Atmel microprocessorsthat arc in svstem prograrnmablc.lipres D-1 .rnd D 2 shol, ThecableA\'R hardwareand the userlntcrfacesofnvarerespectir.c\r tt::l:lr:: Figurc D-l TheCableAVR Hodwte 475 476 file l8n.lection levice lelp ChipsP,ogramfiedl TyFelÄTmEgal:E Oevice Specielüptions I 5eclitli llEr:=]l None :l BDll Lond5ecodl,' andSecL.rtily Bits P FgmFr..rse :l ryqqlry: I |7 l-i7 T f,heck5ilnalwe Elenkrlheck PsmC0DE{FL.ASHI Ve l! CBDE lFL.AsHl I H q mU A I A L t L l - F i U t o l J ]3l:l]Z ,lü98 0irlE09 l{tFFF FLÄSHSIZF: TEPF0MSIZE: FLA$HCSLIM: E€fRüM [5Uf'{: Er€3e DATAIEEPBFMI f- Pre+erve l'- lerify0AT,q EEPF0MI Prrgföm Fl"!h lProgrEmlArea )ji Ve [, D"r Hetsd t-l i Ltäst I üz Conrlel}tionslatus:Connectsd Figure D-2 Pori:f,'M] ProorämI etank checr I u"g I !r;r , TheCobleAVR Softwore SOFTWARESYSTEMREQUIREMENTS and softrvarerequiremcnts to enslrrethat the programmcrPC The minimum l.rardware aoolication oDcrates correctlv are as follorvs: . 100%IBM compatible386DX or higherprocessor(minimumof 486 recommended) . Windows 95@or higher . lYinimum4MB RAM . I'linimum IMB free hard disl<space . SparePC serialport A??endix D lattalif,g aid U'i"g TtreCableAVR GETTING STARTED SOFTWARE INSTALLATION | . Placeth€ diskeftelabeled"lnstallationDiskette I of 2" in Roppydrive (A: \ BJ 2. SelectRun from the Windows Start menu. 3. ClickBrowse. 4. Navigate to the floppydrive(A / BJ ändclickOpen. 5. ClickOK on the Rundialogbox. 6. An introductoryscr€enappears. 7. Follow the on-s€reenprompt! to completeinstallationof the software. On completion, the installation program installs the "TheCableAVR" icon within a new program group called "TheCable." To launch the softwarc, double-dick on the TheCableAtrR icon. HARDWAREINSTALLATION - PlugThecableAvR programmer into a serialpon on the PC. - Connectthe IDC plugto the l0-pintDC connectoron th€ targetboard. - Apply power to the targ€t board.CrheCableAVR drawspower from the targ€r board.) - S€lectConnection from üe Fil€ Dull-down menuinThecableAvR software.Inthe pop-upwindowsel€ctthe appropriate COM pon. ClickOK to savethe COt4 pofi selectionandclosethe window. To check the connection between the PC and the programming cable, open up the Connection pop-up window and dick Checlc If everything is connected corecdy, a messagc pops up, "TheCableA\.R programming cable is corectly conrected." Ifcommunication enors are encountered, make sure the target board is powered on (the powcr LED on the programmer should be 1it). A1so,ensue that no other software or hard waft is conflicting with or using the selectedCOM port SOFTWAREOVERV!EW TheCableA\rR software al1owsthe user to select the g?e ofprocessor to be programmed, the afeas(s)ofthe processorto program, and the security level to program. The software also allows the user to open and edit hex or binary liles for the flash andlor data area of the processorto be programmed. TheCableAVR software can also be called from the command line. This allows other aooli cation. to open 3nd run TheCableAVR direcdy. 477 474 MAIN SCREEN TheCableAVR software main screen can be divided into six sections: pull down menus' Device Parametersframe, Flash (prognm) Area frame, EEPROM Area ftame, Statistics frame, and control buttons group. Figure D 2 shows the main screen ofTheCableAVR PULL.DO\^/N MENUS There are four main putl-down menus available: File, Connection, Device, and Help File Menu: . Open Proiect Pmmptsthe userto selecta previouslysavedpro,€ctto open andload. . SaveProject-Prompts üe userto sel€ctä proi€ctfilenameto savethe current settings underfor fü$ire reference. Load Butrers-lt a file is sel€ct€dfor the Flashand/or EEPROMbuffers.load the file into the buffer. . Export Proiectfor PalmPilot-op€ns a window for downloadingthe project to softwarerunningon a PalmPilotor similardevice. TheCableAVR Companion . Exit-Clos€sthe aDDlication. Connection Menu: . SelectPort-opens th€ Connections pop-upwindowto allowthe üs€rto selecta COM port. . CheckConnection-AttempB to communicatewith TheCableAVRhardwa.e.lf the messäF"Th€CableAVRproSrammingcabl€is communicationsare establ'shed, correctly connected."appearsto tie user . Disconnect-Disconnecfrom the COM port Uponthe nextcommandwhich with the hardwäre,the connedionis re-established. requirescommünication Device Menu: . Read-Read the selectedar€as(flashand/or EEPROM)into the appropriat€buffer and updatethe checksum field for all read bufiers.Updatethe buffer filenameto FlashBuffor EEPRoM_Bufito indicat€that the contentsof the buffer are from the pro€essorand not a loäd€dfile. . Protnfti Programthe processoraccordingthe options selected. . Verit-Read andveriry d'e processorfor the ar€asselected(flashand/or EEPROIY). lf ar€ detected.the user is informedthat differencesexist and those differdiscreDancies encesare listed. . Erase Performa Chip Erareoperätionon th€ proc€ssor: A!!e4d;x D-Installing and Ur;ng TheCableAYR . Blank Check-Read the flash and EEPROMareasof the chip.lf all memory locations contain oxFEthen inform the user that the chip is blank.lf not, inform the user that the chiD is not blank. . Reset-Perform a Resetoperation on the processor. . ReadSecurity-Read the current security level ofthe processor and displaythe level to the user. . Write Security-Write the selectedsecurity levelto the processor. Help Menu: . AboutTheCableAVR-Display softwareversionandcompanyinformation. . Get CableVersion-lnterrogate TheCableAVR programming cablehardwarefor the versionnumberanddisplaythe numberto the user.lt maybe necessary to callthis twiceto get the versionnumber.Occasionally, the communications are out of sequence andthe versionreadsas0.0, DEVICE PARAMETERS The Device Parameterssection allows the user to selectthe g?e ofprocessor to perform operations on and which areasof the processor to include. The user can also select how the processoris handled during those operations,including whether or not to checkthe signature bltes and whether or not to blank check the processorduring a program operation. There are sevenfie1ds(Device T1.pe,Securiry Check Signature, Blank Check, Pgm CODE, Pgm DATA, and Preserye DATA) and two command buttons (Auto Detect and Special Options) in the Device Parameterssection. Figure D-3 Devi.rePorometers Fields ,l€10 DEVICETYPE Use this drop-down list to select the rype of target processor.Selecting a processor automatically clears the flash and EEPROM buffers and reset the Statistics frelds. Ifthere are Special Options ar.ailablefor the processor,this command button is enabled.The Auto Detect command button automatically selectsthe processorgpe for the user if the prccessor is AUTO DETECT The Auto Detect command bunon automatically selects tle processor gpe. When the Auto Detect comnand button is dicked, TheCableAVR reads the processort signature b1.tesand determines tlre type ofprocessor. The appropriatc Device T1?e list item is then selectedand the Statistia felds are updated accordingly Nate: If tlte qrarcssoris readprotuted ßeearityfue b;a enabhd), tbm inulid signature S,tes aft retumedand tbe tye afPro.essorca not bedetonined. Iftti l)a??ens,a nessageis returned, 'De&e is LacLed.Unatle to determine ry?eof tuone," and tbe Deoie T!?efield ;s not thanged. SECURITY The Security drop-down list allows the user to select fiom thrce levels of securiry These correspond to the lock bits on the processon. Level I No lock bits progmmmed;thedevicecanbe readand written to. . Level2-LB I proträmmed,tB2 not proSrämm€d; tunher programmingof the Flash ändEEPROM is disabied, . L€vel3 LBI andLB2progmmmed;further progrämming ändreading ar€ both disabledfor FlashandEEPROM. The Security level can be read frorn or written to the processorat any time by using the Device pull-down menu items Read Security and Write Security SPECIALOPTIONS The Special Options commard button is enabled for processorsthat have fuse bits that can be programmed. When it is dicked, a Special Options window is displayed to allow the user to set up the fuse bits for that particulrr processor CHECK SIGNATURE When the Ch€ck Signature option is che&ed, TheCableAVR checks the signature b1tes before performing a program, read, or verifr on the processor-lfthe signatL[e bltes do not match the selectedprocessor,the user is given a warning message"Device Signature Erfor" and the selectedoperation is aborted. ,4P?endi,c D-Installihg and Using TheCableAVR BLANK CHECK When the Blank Check option is checked,TheCableAVR automaticallyperforms a blank checkafter the chip eraseduring the programmingoperation.If the processordid not completely erase,the user is issueda warning, "Flash (or EEPROM) Area is Not Blank " and the programming operationis aborted. PGM CODE (FLASH) The Pgm CODE (FLASH) option selects,/deselects the flash areaof the processorfor programming, reading,and blank checkingoperations.Each ofthese operationsis performed on the flash areaonly if the Pgm CODE (FLASH) option is selected.(If this option is not checked,the operation skipsthe fash area.) PGM DATA (EEPROM) The Pgm DATA (EEPROM) option selects/deselects the EEPROM areaof the processor for programming, reading, and blank checking operations.Each of these operations is performed on the EEPROM areaonly if Pgm DATA (EEPROM) option is selected.(If this option is not checked,the operationskipsthe EEPROM area.) Note: If the PreserveDATA (EEPROM) opt;on is selected, the Pgm DAIH (EEPROM) option is selexedand disabled.Part of the PresenteData operationis toprograrn tbe EEPROM area,so this aption hasto beselected. PRESERVEDATA (EEPROM) In order to program the flash areaof the processor,a chip erasemust first be performed. This erasesthe contentsofboth the flash and the EEPROM areas.In somecases,it is desirableto preserve the current EEPROM data in the processor.When the PreserveDATA (EEPROM) option is selected,the EEPROM areaof the processoris readand storedin the EEPROM buffer (ofthe PC application) before the chip eraseis performed. After the flash area is programmed and verified, the EEPROM areais programmed from the EEPROM buffer. Note: If the Pgm CODE (FLASH) option is not selected, this option is not available (because a chip eraseis notperformedduring theprogram cycle). F L A S H ( P R O G R A M )A R E A The Flash (Program) Area section has two main parts-the bulfer information boxes and the command buttons (seeFigure D-4). The buffer information boxes te11what file (if any) Figure D-4 Flosh(Program) Area ,f8l 482 has been selected for the buffer and whether or not that file has been loaded into the buffer. The command buttons control the file selection, loading the buffer from the file, editing the buffer, and saving the buffer to a file. . Browse-The Browse command button oromots the user to select a file to load to the buffer.Once a file is selected,the filenameis displayedin the edit field to the left of the Browse button. . Load-The Load command button prompts the user to load the selectedfile into the buffer.Theprogressbar below the filenameedit field shows how much of the available memory is used by the buffer. . Edit-The Edit command button ooens the Buffer Editor to allow the user to edit the contents of the buffer. . Save-The Savecommand button DromDtsthe user for a filenameto savethe current buffer contents under. EEPROMAREA The EEPROM Area section has two main parts-the buffer information boxes and the command buttons (see Figure D-5). The buffer information boxes tell what file (ifany) has been selected for the buffer and whether or not that fi1ehas been loaded into the buffer. The command buttons control the file selection, loading the buffer from the file, editing the buffer, and saving the buffer to a file. Figure D-5 Areo EEPROM Browse-The Browse command button prompts the user to select a file to load to the buffenOnce a file is selected,the filenameis displayedin the edit field to the left of the Browse button. Load-The Load command button prompts the user to load the selectedfile into the buffer.Theprogressbar below the filenameedit field shows how much of the available memory is used by the buffer. Edit-The Edit command button opens the Buffer Editor to allow the user to edit the contents of the buffer. Save-The Savecommand button prompts the user for a filenameto savethe current buffer contents under. A??errdi,ND-Installing and Using TheCableAI/R STATISTICS The Statistics section displays information about the processorselected,the fash and EEPROM buffers,and the progressofthe operationbeing performed.SeeFigure D-6. Figure D-6 Stotistics Fields Size of rhe flash area of Ehe processot S i z e o f t h e E E P R O Ma r e a o f t l r e p r o c e s s o r Checksum of the flash buffer contents E E P R O MC S U M : C h e c k s u m o f t h e E E P R O Mb u f f e r contents FLASH SIZE: E E P R O MS I Z E : FLASH CSUM: selected selected The progressbars representthe percentcompletion ofthe operationbeing performed.The operation being performed is indicated by a caption above the progressbar. COMMAND BUTTONS There are six command buttons available from the main window: Read, Program, Verify, Erase,Blank Check, and Exit. . Read-Read the selectedareas(flashand/or EEPROM)into the appropriate buffer and update the check sum field for all read buffers.Update the buffer filenameto Flash_Buffor EEPROM_Buff to indicatethat the contents of the buffer are from the processor and not a loadedfile. . Program-Program the processor accordingthe options selected. . Veril-Read and veriry the processorfor the areasselected(flashand/or EEPROM).lf discreoanciesare detected.the user is informed that differencesexist and those differencesare listed. 4U . Erass-Performa Chip Eraseoperdtionon the processor. . BlankCheck-Readthe flashandEEPROM areasof the chip.lf all memorylocations is blank.lf not,informthe userthat inform the user that the chip containOxFE then the chipis not blank. . Exit-CloseTheCableAVR aoolication. E D I T B U F F E RS C R E E N The Edit Buffer screenis ooenedwhen the Edit command button is clicked for either the Flash or the EEPROM Area.'I he contentsof t}re appropriatebuffer (indicatedin the window title bar) are displayed in this window for viewing and editing. The starting addressofeach line is displayedin the left frame.The data ofthe buffer is displayed in the center frame in hexadecimal format. The right frame displays the data as ASCII characters. The selectedvalueis highlighted in blue or a dashedoudine.The dashed oudine indicates that the value will be edited. To select a value, click the value with the mouse and tlpe the new value in the fie1d.The values can be edited as either hexadecimal values(by editing in the centerframe) or ASCII characters(by editing in the right frame). The scroll bar at the right scrolls through the contents ofthe entire buffer. u 0 0 0 0 0 c 9 4 F 2 2 6 0 C9 4 0 0 0 0 0 C9 1 0 0 0 0 0 c 9 4 0 0 0 0 0 0 0 1 0 0c 94 00 00 0c 94 0000 0c 94 t4 {9 0c 9{ a0 00 0 0 0 2 0 0 c 9 4 D 00 0 0 c 9 4 0 0 0 0 0 c 9 4 Ä 1 2 7 0 c 9 4 D 00 0 0 0 0 3 0 0c 9{ 00 00 0c 94 0000 0c 949c 27 0c 94 00 00 0 0 0 { 0 0 c 9 4 9 5 2 7 0 C9 4 0 B ! 0 0 C9 { 0 0 0 0 0 C9 4 0 0 0 u 0 0 0 5 0 0 c 9 4 0 0 0 0 0 c 9 4 0 0 0 0 0 c 9 1 0 0 t ) 00 c 9 4 0 0 0 0 0 0 0 6 0 0 c 9 4 ü 0 0 0 0 c 9 4 0 ü 0 0 D C9 { 0 0 0 0 0 c 9 1 0 0 0 0 0 0 0 7 0 0c 94 00 00 0c 9{ 00 00 nc9126 27 0c 94 üü 00 0 0 0 8 0 o c 9 4 7 2 2 ? 0 C9 4 0 0 0 0 0 c 9 1 0 ü 0 0 c c 0 4 0 8 0 0 1 1 0 0 9 0s 2 1 4 8 2 1 4 8 2 1 4 8 2 1 4 D 4 0 4 0 8 0 0 9 F F F 9 F 0 0 0 4 0 9F F!' 9F FF E5 04 02 00 98 FF EC04 02 00 Ä2 FF 0 0 0 8 0 F A0 4 0 2 0 0 2 8 0 0 F E0 1 0 2 0 0 3 6 0 7 0 6 0 s B 2 0 0 00 0 c 0 F F F F 2 3 S 4 0 0 2 4 2 5 0 0 4 E 5 5 7 7 2 0 5 3 6 5 ? 4 7 0 0 0 0 D 0 6 F 6 9 5 E 7 { 2 0 4 D 6 s 6 D6 F 7 2 t 9 ? A 6 5 6 { 0 0 2 0 u 0 0 8 0 2 0 ? 0 2 E2 n 2 0 2 0 2 0 2 0 2 0 2 0 2 A 2 0 2 E2 0 2 0 2 A 2 0 2 0 2 ! 2 E0 0 6 1 5 1 6 1 6 1 6 1 6 1 5 1 6 1 6 1 5 1 Figure D-7 BufferEditorSoeen tlö&tt ar ll rr lt tt tt tt tl lttrll tti'll tll'll ltl'lt ll ll It It It tt ll ll al It Il II tt&'!r lll I I1'l I r! | | | I | | | l0l I tyty ct Itltall lvill ürt ( brr 6tlll y$T int SZ l|ev sEüp Uernorizsd Zfpeldia D Ia'td ;ag dfld Utiag TbeCable,4I/R 'lb fill a range with a particular vrlue, edit thc Start Add, End Add, and Value {ields at the bottom ofthe window and dick Fill Range. This fills the range ofvalues lrom Start Ada to End Add with Value. To 6ll the entire buffcr with t),rFf, dick Fi11AI-L with 'FF'. All valuesin this sectionshouldbe enteredashcxadecimalnumbers. Click OK to closethe Edit Buffer windowNote: Contentsaf tberebctedballer are nadfzed at tb cl)anges ar. ndde. Iftbe urer i unwre aflhe ehanges naüng, he n he:hoalrl bacAu2 bi:fle BEFORE no.tifr;ng tbe bufer. C O M P O R TS E T U PS C R E E N The COM Port Setup Screen allorvs thc user to select the COM port for connection to TheCableA\R hardt are.Once the port is selected,the hardrvareis connected,and power has been applied to the targct board, the user malr dick Check to check the setup. Ifcvcry thing is corectly set up, the mcssagc"TheCabIeAVR programmingcableis correctlvconnected" appears to thc uscr. Click OK to close rhe COI\'I Port Setup screenand sar-cthc COI\,I port sctup. ABOUT SCREEN The About Screen simplv displays sofnvare version information and contact inlormatron for ProgressiveResourcesLLC. C O M M A N DL I N E S U P P O R T The commandline suppon expcctsparticularparanetersto be passedrvhenthe applicatron is olled. These are: . ProjectFilename (if not in the samedirectoryästhe executable, includethe path). . UserPresentFlag= I Useris pr€sentandmessage box willäppearifan error occurs. 2 Useris not presentandreturnvaluewillhaveto be usedto determineifthe programming wassuccessful. An examplewith a user present would be 'C:\Proqram fiLes\Proqressive ' c: \IrRoJ FILTS\PROJ.isp, 1 Resources\TheCabLeAVR\TheCäbLeAVR.ex. An er.r,rplcs irhouta u.erpre.entwouldbe 'c:\?rogidn FiLes\ rogressive Resources\ThecableAvR\ThecableAVR.€xe' ' C: \PROJ FILES\PROJ.1sp' '0 ' 485 ,|a6 The lolJowingvJues are rerumedby the appllcat;onupon dosing: l1 Unable topßcdTEEPROM 10 Unableto prosm just the EEPRON{ dueto lockeddoice dNtadue lo locl.d d.'iff 9 Unable to pregff 5 Unable to progflm the tu* bits EEPROM not bhnk aftcr!nip cr*c rhe setuitybiß Flsh not blank after chip e6e 3 2 Signarurc docs not match elcctol ddi@ Badveriryof flsh or EEPROMafterprcgrm Unable to $cßsfülly Prcgm I of dwie @Imuniote sced Unable to scce$ wirn TheCibleAVR hddMre ly ompteted vommimtewithTheCableAVRhadwrc 2 U6er cmceled pr%mminA 3 Unable to open s€lectedpmjEt file of device Unable to ooen eithq the Flash or the EEPROM 6le 5 -6 -7 Fldh filc too largc for selccted dcvi@ EEPROM file too largefor the selecteddaic Bad che.kum (hd or ep fils on!) in Flashor EEPROM 6le HARDWARE OVERVIEW TheCableA\.R hardware consists ofa programrning cable that has a 9-pin serial port connection on one end and a 10-pin IDC plug on th€ oth€r. There äre two indicator LEDs on the cable, Power and Busy. The green Power LED is lit any time the cable has power (applied through the target system)-The red Busy LED is lit whenever the cable is holding the taget system in reset to perlorm some programming operation (Read, Program, Verifr. etc.). ,4f?e'dir D If,ttallihg and U'i"E Tlt.Cab/.,4I/R PIN ASSIGNI'1ENTS The 10-pin IDC headeron the targct syst€mshould be pinned out as follows: O 1 2 Prostmma Porcr GVr) NC NC SPI MatcrOutSlaveln o T'I]SO SPI Materln SlaseOut I GND ?rcgrmnd GND SCKl SPI-Ssirr Cbck 9 GND 10 RESET Prosrmmer GND Tdget RESET Connol Pin xlloSt 5 8 NC Table D-l o o ThecobleÄYR sofwo.e Figure D 8 Showsa top view of the IDC headerConnectorshownis rhe male 10-pin IDC connectorasviewedfiom abovethe componentsideofthe target board. l0-Pin IDC Eeader Top View vcc-r NC -1 4+ MOSI 6 <t- Mtso I -----) scK GND-9 Fisure D-8 IO_>RESET TheCobleAVR l0-PinIDCHeader TARGETSYSTEMSETUP For TheCableAVR programmer to work corecdy, cenain conditions must be met r,vithin the target ,|.38 SPI ENABLE FUSE The SPI Enable Fuse (SPIEN) must be ENABLED on the target processorin order for TheCableA\R programm€r to work correcdy The SPIEN tuse can ooly be read./programmed in parallel programming mode. The defautt for the processorsis SPIEN ena6bd. RESETCIRCUIT The serial programming mode of the Atmel AVR devicesis initiated by setting the RESET pin to the appropriate RESET state. So, in order to place the taJget processor in serial programming mode, TheCableAVR hard*.are must be able to externrlly control the state of the RESET pin. PO\'vER TheCableAVR hardware is pou'ered from the target application. Pins 1 and 9 are VCC (+5 \DC) and GND, espectivdy TARGET SYSTE]'I OSCILLATOR The target system oscillator must be mnning for TheCableA\R to accessthe target processor The frequency must be an acceptableftequenry for the target processor The acciptable frequencies can be found in the microcontoller data sheets. Nau: Tbe ascillatarcaaldbe an extenal fftttalreionator or an;ntemal RC oldlatar The MegaAVR-DEV Development Board The MegaAVR-Dev developmentboard by ProgressiveResourcesLLC, Indianapolis, Indiana, is designedfor protoqping and laboratoryuse.The board supportsthe ,AT90S8535,Mega16,Mega163,Mega32,or the Meg a323in a 40-pinDIP package. Figure E-f MegoAVR-Dev Development Board The features ofthe development board include the following: . Comes standardwith an ATMegal6-8PC processor. . Comes preproSrammedwith boot loadint firmware. No other protramming hardware is required.Justconnect the MegaAVR-Devto your PC with an RS232cableand run the "AVRBL Boot Loader"Windows application(available free from: http://www.prllc.com/products/BootApp.zip). 489 490 ' RS-232 throusha 9-PinD shellasw€llasscrewterminalsanda jumperheader. . Up to 32K of in-syst€mproSrämmableFLASHmemory with üp to IK of EEPROM andup to lK of InternalRAM(depending on processorselection). EiSht| o-bitanaloS inputs,usingeitherintemalor user-supplied r€ference. . Nine l/O-controlledLEDS,eight of whicharejumperselectable. . 32 kHz'\^ätch"crystälforon-boardreal-timeop€rations. . A universalclock socketallowsfor "cannedoscillators,"aswell as ä väriety of crystals. c€rämicr€sonators,andpassiveterminations. 0.l" centeredheadersprovideforsimpleconnecionto the processor specialfunction pinsandl/o. . lo-pin.polarized. ISPandJTAGconnections ä.e providedfor in-system programming änddebugSing. MegäAVR-Devs on alsobe progammedthroughRS-232 usingan appropriateboot loaderäpplication. . On-board regulationallowsfor power inputsfrom 8 to 38V DC with an LEDpower indi€aton . T€rmination is provid€dfor 5V DC outputat 250mA. For more information refer to the ProgressiveResourcesweb site http://www.prl1c.com. SPECIFICATIONS 8Vt)38VDC 250mw (nominal) W.1.7inchesx H 1.7inches Mounting Weight Operatingtempmtm 0"C to +607 0"C ro +85"C Humidiry 0)6 ro 95%at +50"C(non-condeqsios) Table E-l MegoÄVR-DevSpe.tltcdtion A?fendix E-Tie MegaAl/R-DEV DeoelapmentBoard ,4._:__l_o@o_ (g)^ - ^|fi' -ll h 3i v] o::.] J.t r'l--i-r.' tLF- !:L 0/6\/ö\ m,,ffvv' 3:" elSl fl33I i "i" oo oo It---llo,El?l q-rno llll llÄ^Rläl T;ö ll" . lol oEEo h oo lld . l9l oEiEo 3.750" 3.250., *ä 3$s! Flsßl? t9t9t | 3tr 3Gn"3 tYl:j- F^ | 4l!l,,3Po'r llilll?*ß"'.s.":/. iä= ifi oo*t ,*'toooooJ. .1ffiffi nn f-v-ö ldEl o z o llll o R o * Ö Öoo YI oo ooo * o f'll'l o ö o JPlo.€! t9-9 lgl Lg-gl lol JPlzolol :-tvl trlol " ölol a------e' 'l:l Hlq r:J t ul_J . iEEiq"El8l3lffi -'',-rEl3l3lffifi i=r"i. :-F : -r JAg lE16öl 30000 3.e50" 3.250" Connections, Heoders,ond Jumpeß ^ i lololo1E}o 5lolololoGEo - 99,,EIT*%%TTI Figure E-2 |;r QoJ o1:Eg-lo I I OEEEO o{-iE-}o " " "..1146oE8o 491 492 SCHEMATIC J J U) 0, U 5= o 0,, u. 0, '6 a o o I t Ct=dB -t-l r$L,oJ 11 tl 3l f' tl RI , E:s3:333 EEs s;;;;üsB 33 E I ur g b0 tt ASCII Table Americar Standard Code for Information Interchanee 000 001 002 003 00'1 005 006 oo7 008 009 010 000 001 002 003 004 005 006 007 010 000 001 002 003 004 005 006 a)7 011 072 013 008 009 004 008 412 014 00c 013 015 01.1 016 00D 00E 015 017 00r 016 020 010 017 421 011 018 022 023 024 025 026 027 o72 013 019 020 021 422 023 011 014 015 016 ot1 00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000 00001001 00001010 00001011 00001r00 00001101 00001110 00001111 00010000 00010001 00010010 00010011 00010100 00010r01 00010110 00010111 NUL soH STX ETX EOT ENQ. ACK BEL BS HT LF YT IF CR SO st DLE DCT DC2 DC3 DC.1 NÄK si}.r ETB 493 024 02s 026 427 028 029 030 031 032 030 031 032 033 034 035 036 037 040 CAN 018 00011000 00011001 00011010 00011011 00011100 00011101 00011110 01F 00011111 US 00100000 00100001 00100010 00100011 00100100 00100101 00100110 00100111 00101000 00101001 00101010 00101011 00101100 00101101 00101110 00r01r11 00110000 00110001 00110010 00110011 00110100 00110101 00110110 SP(Space) 018 019 OIA 018 0lc 01D 035 036 037 038 039 040 050 020 021 022 023 024 02r026 027 028 041 051 o29 042 043 02^ 014 052 053 054 045 055 046 056 u7 057 048 060 049 061 0ll 041 03.r 042 043 044 045 046 047 050 062 051 063 052 053 064 o2R 02c o2D 028 02t030 031 032 033 034 065 05'1 066 055 067 056 070 457 077 058 059 072 073 036 o37 038 039 034 038 060 l)74 0lc 00110111 00111000 00111001 00111010 00111011 00111100 ENI SUB trsc FS CS RS & 6 7 A?fe,d;r F-ASCII 06i 075 062 063 076 077 0lD 03E 03F 00111101 00111111 ? @ 064 100 0,lO 065 101 041 M2 043 o44 045 00111110 066 L02 067 068 069 070 103 106 046 077 707 047 072 073 110 048 111 049 074 7L2 075 113 076 114 04c 077 115 '176 04D 04E 01000000 01000001 01000010 01000011 01000100 01000101 01000110 01000111 01001000 01001001 010010r0 01001011 01001100 01001101 01001110 717 04F 01001111 o 010r0000 010r0001 P 078 079 104 105 048 080 120 050 081 121 051 082 083 722 052 053 084 r24 r25 085 054 055 B C D E l- G H I J K L M q 010r00r0 R 01010011 01010100 01010101 01010110 S T U 086 726 056 087 727 057 01010111 088 130 058 089 131 059 090 132 133 054 058 01011000 010r1001 01011010 X Y Z 01011011 t 091 092 093 734 094 05c 01011100 05D 01011101 05E 010r11r0 095 737 05F 01011111 096 1,lO 060 097 747 061 01100000 01100001 Tatle 495 496 Binar,! r42 099 143 062 063 100 744 064 101 745 098 ro2 066 01100010 01100011 0r100100 01I00101 01100110 { 065 b 103 L47 067 01100111 s 10.1 150 068 h 105 151 069 106 107 152 153 01101000 01101001 01101010 108 154 109 110 111 1r2 160 06B 0öC 06D 068 06F 01101111 01110000 01110001 01110010 113 161 071 \62 072 073 074 075 115 163 764 117 118 01110011 01110101 076 on 01110111 770 078 01111000 77\ 079 01111001 172 '173 07A 078 01111010 174 01111110 01111111 726 176 07c o7D o7E r27 177 07F 124 125 p 01110100 166 779 \20 t2I 122 1,23 01101101 01101110 070 114 116 01101011 01101100 01110110 01111011 t 01111100 I 01111101 J DEL AVR Instruction Set Summary 497 498 ic 5T si ä€ 9C ii ;.e €i .E Z^9 E ;t! z'< p a:x ! dE* iöq ö 9 gE! e s f \, E ,) v 3 j ! xä 6. sg I I 9 i g g € e E E E $ E .e $ TI EI .1 € E E E, & 3 3 * I f ? ü, 3 E p! 3te e E E .9 E \, ä 5 E : E ! 6 ?! ä i T o t e E ; & 5 €; ö * ,3 Ee e 9 i E E i l,t ü t A??endi, G-AVR Instructian 3et Summary E 3 9 I e 6 t ! p ,) äi E :! EJ € 3 ü 6 :i & e # E 8 EI ! E 4! t : ee s g 2 E ü ä d E g.a TE ! ! p ! a I E g €3 f a ! ! .q e : T E a E ? 5 5 E i : 3 o .g 6 i T e & p e e€ g a ! ,) ; ., n 3 : E I E f i i n I 499 500 ft8 ET g€ ä+' 5=a €ä 9E g6 ä: g .9.9 E iiF E E 5 E ! E e ! i5 ;3 dE ä gEI ? l; E t E 3 E g t ! g € e ee ä äEE ! s p E 3 € EI 3 g t f $ s EE € 3 € E .g s. e I & { ü E E 8 A3 # 3 E! i I c g .z t ü e € ! öl E EI I =l fl dtfi ! .{ : ä 'nl9 !tr ;tt ;td E f a f t I fi E I Er 6e 6 €f a ; I A! E A?petdix G-AIIR lxstruction Set Summary 501 Answers to Selected Exercises CHAPTER I *2. Createänappropriate declaration for thefollowing: A. A constäntcalled"x" that willbe s€t to 789. 'Ia9 ; 7 4 9i const int flash x = 789; Notes:/oZ and .,"* are considered the same gpe of memory in non-r'olatile space. An intcgcr (int)value is declaredin this casebecauseit is a 16-bit numbet (+/- 32767 or 0 65535) and is the nert larger size variable g'pe from a character (char or unsignedchar),which is only 8 bits (+/ 128 or 0 255). B. A variable€alled"fred"thatwill holdnumbersfrom 3 to 456. Answer: unsigned in! int f red,. fred; Note: In this case,the numbers are always positive so int or unsigned int will work, but the range ofthe number is such that it will not fit into a char or unsigned c]lar. C. A variablecalled"sensorouC'that will containnumbersfrom - | 0 to +45. Answer: siqned char Note: In this cascthe numberswill fit into a ch2f^ctet(+/- 127). 503 504 D A variable arraythatwill have| 0 €lements eachholding n(jmbersfron -23 to 345. Answer': int aüayl10l; Note: In this case,the numbers are such that they will not fit into a char becausethey can exceed128 (8 bits). E. A characterstringconsumthat will containthe string"Press hereto end". Arrswer: -dsh .onsl cidr prcss_st' .här prpss_sl iPrers inqfl hö!6 iPress ' inqfl -o nö!ö önor, co önor; Nores:fasl and canst are considered the same gpe of memory in non-volatile space.All three ofthese dedantions will result in th€ samegenerated code. E A pointer cälled"array ,tr" tiat will point to an arrayof numbersranSingfrom 3 to s67Answer: unsiqned iuE *arrayjtr,. Notes:\4lhen declaringthe type ofa pointer,it is not the sizeof the poinrer bur what it rs pointing to that is of concem. In this case,the pointer is pointing to ralues that are larger than 8 bits but will easily ft into a 16-bit integer G. Us€an enumerätion to set"uno","dos",'tres"to 2l,22,23,respectively. Answer: enun { uno=21, dos, tres }; Notes: The default for an enumeration starting label ralue is 0. So the 6rst must be assigned to the desired starting \due and the subsequentvalues will fo1low. *4. Evaluateastrue or falseas if usedin a conditionalsratement For all problems:x = 0x45iy = 0xc6 A (x =: ox4s) Answer TRUE B (xlv) Arrswer: TRUE (since 0x45 | 0xc6 = oxc?, and 0xc7 is not zero) ApFndix H ln,upr t. S.l. t"d 8..'.t,., c (" Y) Answer: FATSE D (y - &06 == oxc) Answer: 0xC6 0x06 = 0xc0, anil thaE is not {since *6. E!äluate the välue of the %riables after the {ra8m€nt of code runs: FALSE Lo 0x0cl = 10; = 10; unsiqned unsiqned char cnLr int value ) while value++; (cncr < 10); // equal = ?2 value cnEr = ?? Answer: value = 11 cntr = 10 Notes: The variable valzr gets incremented, then the value of cn;r is tested but not modified. * | 0. Write a fragmentof C code to declarean appropriatearrayand then fill rhe arraywith the powers of 2 from 2' to 2'. One possible solution: unsisned char x,y; char Ewost6l; /* /* = 1; x!=0xa0; for(a x<<=1) = x; twosly++l /* store size array Eo hold Lhe 6 figures.. */ aleclare a couple of indexes a one left /* shift until it walue into array and incrment */ is 2r */ index */ CHAPTER 2 *2. Describethe followingmemorytypesänddelineare their uses: A. FLASHCodeMemory B. Data l'4€mory C. EEPROM Memory Partial answer: EEPROM memory is non volatile memory used to store data tiat must not be lost when the processorlosespower It has a limited number ofpossible write-clcles and so is usually not used folvariable storage. 505 506 *6. Write a fragmentof C languaSe cod€to initializeExt€rnalInterruprI to activareon a hlling edgeappliedto the externalinterruptpan. Answer cIr.IsK = 0b1x000000r I.' -p _ 0b".xxt0^"j INT //enable '\nt //s-r ,o 1 .Äd. o " :.q - edg- Note: r is not an acceptabledigit, bLit is used to shorv that thc ;r bits do not alfcct thc prob lem. Ody those bits set to I or d actuallv affect the answer *8. Write a fr:gmentof C language codeto initialize the Port C pinsso that the uppernibblecan be usedfor inputandthe lowernibblemaybe usedfor output. //iniLialize PorL c * | L Sketchthe wäveform appearingat the outpur of the USARTwhen it transmitsan "H " at 9600 baud.Thesketch should show volragelevelsand the bit durationsin additionto the Answer: From the ASCII table we find that the code for "H" is 0x,l8 rnd the time per bit is 1/9600 = 104 microseconds. Each column below is one bit and is 104 nicrosecondswide. 0v State äa * | 3. Compute the missiflgvaluesto complerethe followingtable relatingto analogto digital Digitdl Out 4.2Y 10v 107 or Ox6A 1,23 10v 223 10 ,4fien,lix H '1n'tueß to Setetted Erertnt! so7 Answer to line 1 (the rest aie up to you): vt. X 4.2V X 10v 23- 7 o''(" - t) =x=rorro=0*B 10v Note: Becauseof integer math limits, any decimal ponion is dropped from the answer CHAPTER 3 *l- Write a macro usinSthe #define directiveto aliasthe function pu"fidro with a function nameds€nd the-char0. Answer| +define send Ehe-char (a) putchar(ä) *4.writeafunctionthatPrintsitscomPi|edateandtime.UsethecomPi|ertinterna|tagnames to get the date and time val'res Answer: putsf ('\n\rconpile DATE ); PUE6f( putsf { '\rconpile TIüE ); PUESf( Date Tine : :\!'), \r" ) ; Notes: The function 22r9fl prints a flash based string (constant string) to the standard oupur. 508 *5. Write a tunction that inpuB a l&bh hoqd€cirnalvalue:nd then prints the binary equivalent Not€: there is no stand:rd output tunction to print binary---{o it is all up to you! One possible solution: woid put_bln16 {unsigned int walue) { int k; // vorking counter for(k=o, k < 16, k++) t if{value & (1<<k)) puechar('1') putchar('o'); // do 16 aligits lI if // etse plint 2k Et.e\ priDt a '1' a '0' , J Notes: In this example, a 1 is shifted left, crcating a rnask to test each bit position, for all 16 positions of the integer. A "Fast Start" to Embedded C Programming and the AVR This appendix is a tutorial examplc showing horv to enter, compile, and dorvnload a program using CodeVisionAVR, the AVRBL Boodoadu Windows@ Application, and the MegaA\rR-DE\r board. The methods described here may be uscd to enter and test all of the code examplcs and exercisesfiom this tert. I. INSTALLING CODEVISIONAVR Locate the CodeVisionA\rR C Compiler installationon the included CD in the 'CODE\'ISION EVAL" director,v Run setup.exe to install. Install the Codev; .ionA\rR compiJer inro rt'edefauJr dire,r.rry: -:\cr':rw".lfrhere is an old re,qinro' CodcVisionÄVR present, you mav install thc nerv one over it. AIso on the first run, undcr Windows@ NT4, 2000, or )Q you must use Administrator privileges. On subsequent runs, PowerUser privilegcsmay be alsoused. 2. INSTALLING THE AVRBL WINDOWS APPLICATION Locatethe AVRBL appJicationsetupon the includedCD in the 'AVI{BL APP" di rectory.Run setup.exeto install. Insta[ the AVRBL applicationinto the defaultdirectory:.C:\Program Files\AVR Boodoader\AvRBootloadcr.exe". To properlyinsta11 the AVRBL applicationunder Windows@NT4, 2000, or )G, you must have Administrator privileees. 3. SETTING UP A CODEVISIONAVR PROJECT First, createa folder in the "C:\cravrY directory called "test". Your resulting path la'ill Open the CodeVisionA\rR appJication and create a ncw file. Nerv projects are created with thc File lNew menu command or by clicking thc Create New File button on the toolbar. These actions open the Create New File dialog box as in Figure I-1, 509 5t0 requesting that you specify the type offile to open. Select the Project option and click OK. A second dialog box asks you to confirm use of the CodeWizardAVR to create the new project. This dialog box is depicted in Figure I-2. Figure l-l CreoteNewFileDiologBox To create a project without using the code rdzard, selectNo when prompted to use it, Figure f-2 CodeWizardAVR ConfirmDialogBox A final dialog box prompts you to specifi a project file name and location. Select the "C:\cvaw\test" folder that you created earlier, and place the project in it, named "test". When these steps are completed, CodeVisionAVR creates a new project and opens the Configure lPmject dialog box for the new project. This dialog box has severaltabbed frames ofoptions that allow you to customize the project for your specific application, as shown in Fizure I-3. Ä??end;|a I-A Figure f-3 "Fast Start" to Enbedded C Pragrammixg and tbe AVR CodeVisionAVR ofterCreotingo NewProjea The project is configured with the ProjectlCon-figure menu command or the Project Configure toolbar button. Selecting either of these opens the Configure Project dialog box. There are three tabbed frames in this dialog box Files, C Compilär, and After Mak;. The C Compiler tab, sho.wnin Figure I-4, allows you to set properties for the project pertaining to the target device and the executableprogram file. Slt 5t2 Figure I-4 ConfigureProjeaDiologBox A2?endi,c I-A "Fatt Start" ta Ettbedded C Ptagramrning a d tbe Al/R In this dialog, make the following selectionsunder the Code Generation tab: chip: clock: ATmegal6 6.000000 MHz Al1 the other settings should be left in the default condition. Click OK. Next, select File lNew from the menu and Source from the pop-up window, as shown in FizureI-5. Figure f-5 Pop-Upwindow NewFileType This will create a file "Untitiled.c" in the CodeVisionAVR worksoace. Savethis emotv file as"test.c"in your "C:\cvaw\test" project directory. Now, going back to the ProjectlConfgure menu, bring up the Configuration dialog box. Under the Files tab, click the Add button and select the "test.c" file you added to your project directory. The resulting window should appear as it does if Figure I-6: 513 5t4 [:\cvavr\Progs\Test\test, Fri Figure I-6 ClickOK. ProjeaConfigurotion---Files Dialog A?f.ndia I-A "Fast Sta,t" to Enbedd.d C ProgranninS and tlre ,4IlR 4. WRITING SOMETEST CODE Enter the codebelow.It wil setüp the USART at 9600 baud and senda messageevery % secondout to the PC. You will notice that it rcally doesnot take much codeto make thingshappen. +incLude < M E G A 1 6 .h > +incLude +incLude <stdio,h> <de1ay,h> // USART Baual lahe: UCSRA=0x00; UCSRB=0x04; UCSRC=0x46; UBRRH=0x00; 9600 { printf( I'n a C coding delay_ns{500); eeniusl l\n\! ); 5. COMPILING SelectProjectlMake to compileyour code.You shouldget a resultingpop-upwindow titled 'Information," asshor.n in FigureI 7: 515 5t6 [hip:ATmega16 gpe:Application Program Memory model Small fealures: inl,width char toin[No core inshuctions: 0n tegister allocation: 0n Stack area: 60hto1SFh Stack size: 256byte[sJ DataStack usage: 26byte[sJ Stack area: 160hto45Fh Stack size: 768byte[s] usage: 0 byte[sJ{0.02 ofEEPR0M] size: 47Swords [5.82ofF|-ASH] Figure I-7 CompilelnformotionPoFUpwindow Ifthere are any errors or warnings, you should go back and review the code that you entered and make sure it matches the code in Section I-4. If it is correct and there are still errors, check the project settings and make sure that they match the settings called out previously. ,4?Penlir I 6. DOWNLOADING A "F0rt Stdrt" ta Enhedded C Progranning and the,4VR TO THE MEGAAVR-DEV BOARD The MegaAVR-DEV board has a serial connection that can be used to download code using the AVRBL Windows application.P1 is a standardDB-9 connectorusuallyusedto connectto a PC. JP10 and JP12 arejumperswhich connectthe processorserialsignals (RXD and TXD) tollrom the RS-232 driver chip. The sejumpers must be in placefor the RS-232 serialconnectionto work. Open the AVRBL Windows application. JslÄ| AllSettings Info File Defuult StartBootloader [har --l [amPortSeleclion: lilr Jump t,:Eootloader [emmend: i$ llharacter: Baothader Aclive EaudRateSelertirn: t: $tartDownload 5*querrce: lur$ Bootloader Heedy: Ihararter: withErrorr, li- I'drite: EEFH0h,i ltApplicalion Iode tlode EEPHtIM ll:\cvrvr\Test\iest.hei r WaitfarEnotloader thenDownload Statur:ldle Figure f-8 AVRBLWindows ApplicotionMoin Screen ffi !ttt:,,!| Jump toBo'ltl':ader thenQownload 517 5t8 Set the Comm Port Selection, shown in Figure I-8, for the appropriateport to your PC connection.Set the Baud Rate Selectionto 19200. Browsethe Application Code and select your "C:\cvavr\test\test.hex",generatedby the compiler Apply power to your board according to the MegaAVR-DEV datasheet.Click on the Wait for Bootloaderthen Download button on the AVRBL Windows application, then press the reset button on your MegaAVR-DEV board. The statusbar should indicate that the program is being downloaded to FLASH. When it is comDlete. click OK. 7. THE THRILL OF VICTORY Return to the CodeVisionAVR IDE. The SettingslTerminal menu will bring up a dialog box, as shown in Figure I-9. Set up the terminal Baud rate for 9600 baud and the appropriate Port port to your connection,and click OK. Fort: lffi H':rnrs: r ETS/Crs f- 0TR/DSR llolumns: stopnitr, lTl ,d,ppend LF ün FEcEption F Fmt: Farity: lN.rreI lv LJnlransm$srDr'l Errution, lä[ F Echo Eaudrut"' lffil outub;*: fE-lf tl Figure f-9 w m li l'lone f lnn,fidf il !- I J( ru*a| ? E'rp I Terminol Settings DiologBox Selectthe ToolslTerminal menu item. This will bring up a terminal window and should displayyour results.The line "I'm a C coding Geniusll" should appearevery1,/z secondin the terminal window. You can now go back and play,changing,embellishing,and tailoring the program to your own taste. Rememberthat the CodeVisionAVR terminal window will needto be closedbefore downloadingyour updatedprogram using AVRBL to avoid a port conflict. Good 1uck,and nay the force be with you. SYMBOLS : (colon),29 . (dot),18,54 3 ; Gemicolon), // (slash-s1ash), 3 18 [] (bracket), button,214 ( ) parentheses, 9-10, 12 /* (slash-star),3 ./ 3 Gtar slash), > (indirection), 18,45 & (address-of operator),18,41,43 * (asterisk) ascontentsofoperator,18 asindirectionoperator,41, 43 aspointer operator,57-58 + button,214 = (equ,lsisn),12 ## operator190 % (percentsign),180-81,185-86 (pipemark),181 " (quotationmarks),3-4 ' (single quote),7 4 _ (undeßcore), . (lessthan sisn), 188 > Grcat€rthän sign), 188 \ (backslash), 7, 191 (braced, 3 {I A ACO (analogconparatorout) bit, 146 ACSR (analogmmparatorcontrol and statusrcgister),146 ADC (analog-to-digitalconverter), 747 46 ADC Clocklist box,237 ADC lntemrpt checkbox, 237 ADC tab (CodeWizardÄVR),237 38 ADCSRA (ADC control and status r$ster\,r42 43 ADCW register,143 Add bunon Conigure Projectdialog box,211 Confgure Tools dialogbox,228 13 Address-of(&) operator,18,47, (ADC ADMTIX multiplexerselect register),142 43 Alt+G key conbination, 213 5t9 520 ArralogcomparatorperiphenJ,1,t,649 Analog interfaces,141-51 AND bitwise operator,13-14 AND logical operator,15 Anemometeß,274-:77 Arithmetic operaton assignment and,12 14 rulesof precedence, 12 q?e castingnnd,10 Arrals tunctionaliq, a5 47 multidimensional,47-49 ofstructures,56-57 Arow keys,211,225 .asmertension,22021 Assemblylanguage,160-63 Assignment,arithmeticoperaton ,nd,12-14 Association, opemtonand,18 ASSR (asyrchronousstatusregister),128 Asterisk(-). (S,r,- (asterisk)) Aslmchronouscommunicairon,132-34 Asynchronousstatusregister(ASSR),128 AtmeL (Seeentr;esbeg;nn;nguitl) AIzR) Auto reserved word,9 Automatic storageclass,9 AutoStepcommand,251 AVR rricrocontrollers.(Seea/ra CodeVisionÄCRC Compiler) analoginterfaces,141-51 architecnral overview,88 89 characterVO tunctions,173 CodeWizardAVRand,230 compileroptions,216-17 intenuptsin, 69-70 memory 89-96 parallelVO ports, 105-6 resetand interupt frmctions,97-105 RISC assemblylanguageinstruction set, 16H3 serialcommunication via I2C, 158 60 serialcommunication via SPI,151-57 serialcommunicationvia USARI, 732 41 timer/counters,109-32 AVR Studio debugger,2,l953 B Backslash(\), 7, 1e1 Backspace key 248 Barcrli,erdrc Vessnre,272-73, 294 Batteryhealth,283,305,314 16 Beepermanagement, 316 18 BEL character,7-8 .bin extension,224 Bitfields,61-62 Bits counterselect,110,115 tunctionality,61-62 fuse,226 wGM,124 Bitwise operators,13-14 Blockdiagrams,26769 Booknarks,213 Boot loading,226 Braces[ ],3 Bracket[ ],18 Breakcommand,250-51 Breakstatement,27-28 Breakpoints,25l52 Browsecommandbufton, 250 Build and tcst protoqpe hardwarcphase, 262,294307 -BUILD macro,201 c C compilers.(Sc Code\rision-A.CR C Compiler) Callacfunctlon, 219 Case sensitivitn 4 CBI assemblylanguageinstruction,66 Celebrationphasc,263 Char is unsignedcheckbox,219 Characterarrays,,16,48 49 Characterconstants,7 Check Erasurecheckbox,227 Check ResetSourcecheckbox,232 Check Signaturecheckbox,227 Checksum fi eld (Chip Programmcr), 224 Chip field (Chip Programmcr),216 Chip list box (CodeWizard-{VR),232 Chip Programmerbutton, 223 Chip Programmerdialog box, 22327 Chip tab (CodeWizardA\rR), 232-33 Chips,226-27 Clearingbreakpoints, 251 52 Clockficld Chip kogrammer,216 CodeWizard-{\rR,232 codevision {cR c compnei (seealso CodeWizardA\rR codegenerator) ADCW register, 1.13 rusembly language and,160,163 AVR microcontrollcrs and,205 6 AVR Studio debugger,249-53 compileroptions,216-20 compiling/makingprojects,220 22 formatspecifications, 180 81 IDE operation, 206-16 nestingfiles,188 programming targetdevice, 222 29 queues, 141 serialcommunicarion, 134 SPI and,155 stacksand,93 termiral tool, 247-49 ,CODEVISIONAVR macro,201 CodeWizardA\rR codegenerator ADC tab,237 38 Chip tab,232-33 ExternalIRQtab, 234 functionalitl', 205,229 32 Portstab,233-34 Projectlnfornation tab,238-39 Tirnerstab,235-36 USARTtab,23637 CodeWizrrdAVRConfrm dialogbox, 207-8 .cofextension, 249-50 COFF fiIes,250 Colon(J,2e Comments, 3 Communications Paramctcrs list box, 236 37 Comparemenu(Chip Programmer), 225 Compilation conditional, 191 92 ofprojccts,220 Compilebunon,220 Compoundassignment operators, 17 522 Concatenating panmeters, 190 D Conceptdevelopmentphase,257, Data stack,93 -DAIE macro,201 DDRx register, 11,91,105,233 Debus nenu, 250-51 Debugging AVR Studio debugger,249-53 conditionalconpilation and, 192 Sta& Erd Markerscheckbox,220 termlnal tool for, 247-49 Decrement opemtoß,17,44 Default statement,27 #definedirective äliasoperationand,61 comm€nts,8-9 tunctionality,189 91 PWM example,72627 astel:tualsubstitutiondirective,62 Defnition phase,25860 Defnitions,7 9 Delimiters, 3, 188 Derefcrencingoperator(.), 41 Designphase,26061,284 87 Dew pointcomputation, 281-B2 Digital tachometen,274 Directi.es, preprocessor(SeePreprocessor dnectives) Division operations,12 Do/while loop,19, 27-22 Dot (.), 18,5a 263-64 Conditional compilation,191-92 Conditionalerpressions, 17 18,26 ConfrgureProjectdialogbox COFF files,250 compileroptions,221 IDE operations,208-9, 217 12,216 ConfigureTools dialogbox,228 Constresenedword,6, 63 Constrnts character,7 dedaring,6 functionality,6-7 memoryand,d 63-{5 Continuestatement,28-29 Control statements breakstatement,27-28 continuestatement,28 29 d,o/whtleloop, 19,21-22 goto statement,28-30 itelse statement, 19,23 26 for loop,19,2223 switch/case stntement, 19,26 27 whneloop,3,19-21 Conversion,measurement units, 324 25 Counterselectbits,110,115 Counters.(SreTirner/counters) CR (carriagereturn) character,8, 1,{0 41 CreateNew File button, 207-9 Ctrl+I keycombination, 214 Ctrl+M keycombination, 214 Ctrl+U key combination,214 E EdiIIEEPROM menucommand,224 EditlFind in Filescommand,27576 EditlFI-ASH menucommand, 22,1 Edit Goto Line menu command,213 Editing ExclusiveOR operator,13 Expressions, 12.(Sa alraConditional files,21114 time and date,335-39 Edit Jump to Bookmark menu command,213 ExternäI]Rqtab (CodewizxrdAvR), 234 ExternalSRAtrltWait Statecheckbox,219 Edit Match Bracesmenu comrnand,214 Edit Print Selectionmenu cornmand,214 E EditlToggle Booknark mcnu comnand,213 F9 ke1,220 FALSEvalue,14-15 Feasibilitystudies bärometric prcssure, 272-73 battcry health,283 d€wpoint computation,28182 l:rlmtditr, 273-74 measr.rement considerations, 269-70 purpose,258 rainlall,278-81 realtime considerations, 283-84 temperat'.re,270-72 rvindchill computation,28283 wind direction,27778 vlnd speed,271-77 FF character,8 FIFO (tustin,6rst out),135 -FILE macro,201 File OutputForma(s)Jistbox,220,250 File CloseProjectmeoucommand,209 File Generatc,Saveand Exit menu command,239 FilelLoadmenucornmand, 224 FilclNew menuconmandl207,209 FilelOpenmenucommand,206,209 FilelOpenObjectfile menu command, 250 .eepextens;on,224 EEPROM memory AVR microcontrollers,89, 94 95 compileroptions,217 making projccts,222 programmingtargetdevices,22328 v:riablesand, 63 65 Eeprom reservcdrvord,63 8 bit enumsoption,219 sBIT ENUMS. MACTO, 201 Electricalspecification,266 #e1ifdirective,191 92 #elsedirective,191-96 EnableWarnings checkbox,220 End Address ficld (Fill llemorv Block),225 End fieJd(Chip Progranmer),22a End ke11211 #endif directivc,191-96 EnhancedCore Instructionscheck box,219 Dnum resen'edword, 8 Enumerations,7-8 Equalsisn(r, 12 #errordirective, 200 524 File PageSetupmenucommand,214 File Print menucommand,214 Files editing,211-14 navigatingthrcugh, 21+16 nesting,188 openingfor debugging250 printing, 214 (SeeSourcefles) source. FilelSaveAs menucommand, 209 FilelSavemenucommand, 224 Fill Memory Block dialogbox,225 Fin Valuefreld (Fill Memory Block), 225 FI-ASH Lock Bits frllne (Chip Prosammer),226 FLASH memory AVR microcontrollers,89-90 compleroptrons,rrl-ly constants and,63 64 makingproj€cts,222 prcgxmming targetdevices,22328 put:fl) fonctton,178-:79 smnfl) fmction, 785 Flashreservcdword, 63 For loop, 19,22-23 Frequenry,124-26 Functions tunctionality,33-34 giobalvariables,5 { VO functions.(SeeVO functions) local rariables,5 pxssingstructuresto, 55-56 pointersto,49-51 prototrying,34 36 recursivc,3T38 returnralues,36-37 syntacticalrules,4 Fusebits, 226 G gexba4) f'rnctton CodeWizardAVRand,236 example,34 tunctronaltty,172-78 standardinput füctions, 183-88 geaj tunct1on,7a4-85 GICR (generalinterrupt control register), 98,100 Global variables,5-6, 66, 94 Goto statement,28 30 Greatc than G) sign,188 Grouping operators,18 H Hard*ure, weathermonitor project,262, 284-90 Heap space,219 HEAP SIZE_ macro,201 -HEAP_START macro,201 HexlASCII button, 248 Hex Codeedit box,248 HEX fomar (Intel), 160-62,22a Home key,211 HtlIrdlq, 273 :74, 294, 305 I I/O tunctions cJraracter functions,172 78 turctionaliry, 177-:72 standnrdinputtunctions,183-88 standard ouQuttunctions,178-83 I/O opcrations, 11,72,88 I/O registers, 66-69,89-92 I2C (Inter-Integrated Circuit),158-60 ICES1 (inputcaptureedgcselectbit), 116 ICNC1 (inputcapturenoisecanceller bit),116 (input ICP capturepin), 116 116-19 ICR1 (inputcaptureregister), IDE (integrated dcvclopmcnt environment), 206 16 #ifdirective,191-92 Itelse statement, 19,23-26 If statcment, 23 2,1,21,1 #ifdefdirective,191 96 #ifndefdirective,191-96 In SystemAVR Chip Programme', 222 23 #includedirective fünctionaliry3,36, 188 headerfilesand,67 I/O rcgisters and,92 interruptvectors,99 100 Incrementoperators, 16,44 Indentingblocksof text,213-14 Indexes, queues and,135 36 (->),18,4s Indnection Indircctionopcrator(.), 41,,13 Input crpturemode(Timer 1), 115 19 Input lirnctions,183-88 Interfaces, analog,141-51 1vord,70-71,99 Inteüuptreserved Interrupts AVR microcontrollers,97-101 CodeWizardAVR and,230,236 initializing, 98 real-timemethodsand,69-72 rcset,97, 101 5 sedalcommunicationand, 17,1 USART and,135 ISR (intcrupt scn'iceroutine) AVC microcontrollers and,97, 99 100 real-timemethodsand,69-72 SPI and,155 57 K Keycombinations Alt+G keycombination, 213 CtrI+I keycombination, 214 214 Ctrl+M keycombination, Ctrl+U keycombination, 21,1 Shift+Ctrlkeycombination, 213 Shift+F3 key combination,250 221 Shift+F9keycombination, Shift+tb key combination,225 Keywords.(saaReservedwords) L Labels,29 Largcmcmorymodel,218 Left shift operator,13 Lessthan(<)sign,188 LF (linefeed)character,8, 140 41 LIFO (lastin, firstout),93 #üne dnective,200-201 LINE macro,201 Linking,160 526 Local variables,5, 9 Logicaloperators, 14-15 LUTs (look-up tables),47, 340 M Machinestate functionality,75-80 viewins/nodii,ing, 252 53 Macros,predefined,200-201 main) tuncnon CodeWizardA\R and,230 tunctionälify,23 globalvariablcs,5 6 Makebutton,221 Making projects,221-22 Mallot finction, 219 Masking,14 -MCU_CLOCK FREqUENCY macro,201 MCUCR (MCU control register), 100-101 Measurementconsiderations for design, 269 84 Mediummenorymodel,218 Memberoperator(.),54 Memory AVR rnicrocontrollers,89 96 bits andbitfields,61 compileroptions,217-18 sürctures and,58-59 typesol63-69 unionsand,58 59 lvremorywrnooqz)l Microcontrollers.(Sa AVR microcontrollers) MIPS, 88 MISO (masterin slave-oudpin, 152,157 Mode Iist box,234 -MODEL SMALL_ macro,201 MODEL TINY_ macro,201 MOSI (master-out-slave-in)pin, 752,757 Multidirnensionalarrays,47 49 Multiplication operations,12 N Navigating61es,21416 Nesting6les,188 NTC (negatic temperaturecoefrcient),270 Numeric constants,7 o Object 6les,250 OOP (object orientedprogramrning),5,1 Open File button, 206,209 OpenFile dialogbox,206 7,209 Operational spccificatio n,266-67, 324 Operators address-of, 18,41,43 arithmetic.(SeaArithmetic operators) associationoi 18 bitwise,13-14 compoundassigrment, 17 concatenatingparameters,190 decement,17, 44 defined,12 dereferencing41 groupin& 18 increment,16, 44 indirection,41, 43 Iogical,14-15 rnember,54 pointer,5T-58 relational, 14-15 12-73,75,14 19'44 rulesofprecedence, srzeof,62-63 gpedel 60-61 277 Opticalencoding, Optimization Level setting 218 Optimize for setting,218 -OPTIMIZE SIZE- macro,201 OPTIMIZE-SPEED macro,201 OR bitwise operatoa13-14 OR logical operator,15 Ordering functions,34 Outputcomparemode(Tiner 7),11922 Output compareregiste\ L19,727,725 Outputfunctions,178-83 P PageSetr.rp dialogbox,214 PageDownkey,225 PageUpkey,225 ParallelI/O ports,105-{ Parameters, concatenating,190 ( ), 9 10,12 Parentheses Percentsign(%),180-81,185-86 PlNx registea 91, 105 Pipemark(l), 181 Pointeroperätor(*), 57-58 Pointers tunctiooaliry 41-45 to functions,49 51 memoryand,65 seanfl)tunctron,7&5 to structures,57-58 Poppingdata"93 94 Poftinüaliz non,91 92 Portstab (CodeWizardAVR),233-34 PORTx register,91, 105,233-34 Potentiometeß,277 #pragmadirectir€, 196 200 #pragmalibrary direaive,200 #pragmaopt directive,197 #pragmaoptsizedirective,197-98 #pragmapromotechardirective,199 #pragmaregallocdirective,199 #pragmasaveregdirective,198 #pragmauchardirective,199-200 #pragmawarn directive,197 Precedence bitwise operators,13 logical operatoß,15 rulesfor operators,12, 18-19 unaryoperators,44 Preprocessor directives (See #defne. #de6nedirective) #eßfdlrectle,l91 92 #elsedirective,191-96 #endif directive,191-96 #error directive,200 tunctionality,172,188 #rf dnecnw, ß1-92 #ifdef directive,191-96 #ifndef directive,191 96 #include.(Jee#includedireaive) #line directive,200-201 #pragmadneaive, 196-200 528 Preprocessor directives(cazräzal) #undef directive,191 #warningdirective,200 PreserveEEPROM checkbox,227 Printer button, 214 ptinfl) futction characterstrings,49 CodeWizardA\R and,236 corrpileroptions,218 e-xample, 3 tunctionaliq.,180-82 while loop and,20 Printingfles,214 Priority, interruptsand,97 Programmenu(Chip Programmer), 225-27 Progam Tlpe list box,233 Pro$am T}?e sefting,218 ProgramlAll menucommand'226 27 ProgramIBlankCheckmenucommand,227 ProgramlEraseChip menucomrnand,227 ProgramlFuseBits menu command,,226 PrcgramLock Bits menr command,226 Progamming automatingFocess,227 projectphasesinvolving 26G63 speeding up,227 standardsfor, 80-81 targetd.ev:rces, 222-29 weathermonitor project,286-87, 290-92,301 39 ProjectConfiguretoolbarbutton,208 9 ProjectInformation tab (CodeWizardAVR),238-39 Project Compile File menucommand,220 ProjectlConfiguremenucommand,208 9, 276,250 ProjectlConfgure lC Compiler menu comrr;alrd,221 ProjectlMakemenucommand,221 Projects.(SreaÄaWeathermonitor project) dosing,209 CodeWizardA\R and,238 39 conplt:ng,22} 21 configudn&208-9 creÄig207-8 making,221 22 open\n9,206 7 Promotccharto int checkbox,219 Protogping, 34-36, 262,294 301 PTC (positivetemperaturecoeffcient),270 Pushingdata,93-94 puxharj tuncnon chancterI/O functions,178-83 chrracterstring example,46-47 CodeWizardA\R and,236 {inctionatity, 172 78 :79 ?xß0 f\tncnon, 178 Patsfl Äncno\ 779-80 Pl\M (pulsewidth modulation)mode, 123-24 q Qreues,135 36 fuotation marks("), 3-4 R R/W (read,twrite)memory 89 Raingauge,278-81, 286,293,3056, 321-23 In,let RAM (randomaccessmemory),6 Readmenu(Chip Progrzmmet),22527 ReadlChip Signatue menucommand, 226-27 ReadFuseBits menucomlr, nd,226 ReadLock Bits menuconmand,226 Real-timemethods interrupts,69 72 Real-Time Executir"e,72 74 statemachines,75-80 ReallacFnciton,219 Receivercheckbox,236 Recursivetunctions,37-38 RegisterFile, 65 Registerstorageclass,9, 65 Registervariables,65-69 Relationaloperaton,14-15 Removebutton,211 Resewedwords,4 ResetChip button, 248 Resetcommand,251 Resetintefupt, 97,101 5 Resolution,124-26 RETI machineinsmrction, 69,97, 1,00 Return address,slstem stack,97 Returnvalues functions,36-37 structuresand,55-56 RF telemetry, 306-12,318-21 Right shift opemtor,13 RISC microcontollers.(SseAVR microcontrollers) .romextension, 224 ROM (read-onlymemory),6 RS-232medium,134,247 RTC (realtime clock), 158-60 RID (resistivetemperaturedevice),270 RTOS (Rerl-Time OperatinsS)'stem), 72,14 RTX (Real-Time Execnive),72-74 Run command,25051 Run to Cursorcommand,251 Rx File button, 248 RXCIE maskbit, 135 s SBI assemblylanguageinstruction,66 SBIC assemblylanguageinstruction,66 SBIS assemblylanguageinstruction,66 scanf) f'unctton CodeWizardAVRand,236 compileroptions,218 frrnctionality,185 86 pointen and,44-45 SCL (SyncbronousClock), 158 SDA (Synchronous Data),158 SEI assemblylanguage instructioo, 99,107 SelectDeviceand DebugPladorm dialog box,250 Semicolon(J, 3 Sendbutton, 248 Serialcommunication characterVO functions,172 I2C, ß8-60 sPI, 151-57 terminaltool, 247-49 USARI 132 41 Seningbrealgoints,251-52 Settingsbutton, 228 529 530 ScttingslDebuggermenu command,250 making projccts,222 SettingslEditormenu command,214 $canfq fanction, 187 SettingslProgrammer menu command,223 variables and, 63-6ul SettingslTerminal menu comrnand,249 Sfrb compilercommand,11,66 69 volatile modifier and, 66 SREG (statusregister),91,99 Sfrw compilcr command,7l, 66-69 ss Glave serecd Pin,152 Shift+Ctrl kc]' combination,213 (s)scanfFeaturessetting,218 Shift+F3 kev combination,250 sscanJl tunctioo, 187 88, 218 Shifr+F9 key conb;nation,221 StackEnd Nltarkerscheckbox,220 Stackpointer (SP),93 95 Shift+Tab kcy combination, 225 ShorvNcxt Statementcommand,251 Signatures,226-27 Singlequote ('), 7 Sizeofoperator,62 63 Slash dash (/4, 3 Stacks,92-95,97 Star slash(./), 3 Start Address 6e1d(Fill Memow Block),225 Sh$-srar (/.), 3 Strrt Debuggingoption,250 51 Star field (Chip Programmer), 22,1 Slave/master rclationship(SPD, 152-57 Statcmachines.(SeeMachine st:rte) Small memory model,217 Softwrre development. (SeeProgramming) Staticstorageclass,9 Sourcefiles StepOut Of conmand,251 StepInto ommand,251 add;ng,20911 Step Over comnand, 25 1 codewizard-{vR and,230 Stop bufton,250 creating, 209 generating,239-47 asobject61es,250 opening,209 SP(stackpointcr),93 95 SPCR(SPIcontrolregistcr),153 SPI Gerialperiphcral interface), 151-57,174 setting,218 G)printfFcxtures tf) f.'r,cißn, 182-83, 218 Vr;n Stu{M memory AVR microcontrollcrs, 89,92-94 compilcroptions,216-17,219 Stop Dcbugging option, 250-51 Storagedasses,9, 65 Srings, chractc1,16,,18 49 Structurcs znzys of,56-57 bit6eldsand,61 tunctionaliq',54-56 initializing 55 memoryand,58 59 pointersto,57 58 Subtractionopcrations,12 SwitcVcase statement tunctionalitr; 19,26 27 _-_______ P\\M aranple, 126 28 stat€machinesand,75 Switch encoding,277 Systemcloc\ 217 Slstem integrationphase,262'63, 30119 Systemstac( 93,97 Systemtestphase, 263,294,339-43 T TAB character,8 'f$ key,225 110-14 TCCROregister, TCCR1 register,114-28 TCCRx register, 110 29 Temperznte,270-72,293, 305 Terminalbutton, 247 Terminal Settingsdialogbox,249 Termlnal too1,24749 Testdefinition phase,267-42, 29234 Testpiotog?e hardwareph^se,262, 294-307 Ter.t indenting blocksof, 213-14 substituting.(Jee#define direaive) Ticks,110,112,118 TIME macro,201 Timer0,110 14 'f mer 1,71428 Timet 2,728-29 Timer/counters functionality,109-10 109 prescalers/selecton, Timer 0, 109-14 Timer 1, 114 28 -f lmet 2, 128-29 watchdogtimer, 102 5, 235 weathermonitor project,312-14 Timers tab (CodelÄ4zardAvR),235-36 TIMSK (timer interrupt mask register),120 Tiny memorymodel,217 ToggleBreakpointoption, 252 Tool Seaingsdialogbox, 228 ToolslChip Programmermenu comnand,223 ToolslConfigue menucommand,228 ToolslDebuggermenucommard,250 ToolslTerminalmenucommand,217 Transmittercheckbox,236 TRIIE value,14-15 Tx File button, 248 TXCIE maskbit, 135 Type castingrariables,9-10 Tlpedefoperator,60 61 U UBRR (IJSARI baudrateregister),135 UCSR (-ISART control and status rcsister),135 UDR (USART datarcgister),135-37 IJDRIE maskbig135 Unary operators,18, 43-'44,62-63 #undefdirective,191 UnderscoreL), 4 Unions,54,5860 Unit conversion,324-25 UNSIGNED_CIIAR_ macro,201 usART,73241,772-:74 USART Baudratelist box,236 USART tab (CodeWizzrdA\rR),236-s7 532 v Variables.(S,r aÄ, Pointers) declaring,5 globat,5-6,66,94 identifuing as constants,7 local,5,9 nemoryand,63 65 rcgister,65-69 scopeo! 5 { storageclasses, 9 structuresand,54 slntactical rules, 4 g?e casting,9-10 rypesol, ,1-5 viewing/modi{-ing, 252 Veri$, check box, 227 View mcnu,252 Viewl Registersmenu comnand, 252 Volatile modifi er, 65-66 Vo1t.Rel list box, 237 VT character,8 w #warningd;rcctive,200 \Aratchrvindorv, 252 Wxtchdog timer 102 5,235 \\DTCR (vatchdog timer control register),102-5 Weathcr monitor projcct barometricprcssure,272-73, 294 batteryherlth, 283, 305, 314 16 build and tcst prototvpe hardware phasc, 262,294 307 challenges, 349-50 conceptdevelopment phase, 257, 263-64 definitionphase, 258-{0, 264 69 designphase,260 61 dervpoint computation,2Bl82 hardrvaredcsign,284-90 hrmrdity, 273-7 1, 294, 305 poler supplll286,290 purpose,258 raingaugc,278-81,286,293,305-6, 321 23 realtime considerations, 283-B,l sofnvare design,286-87,290 92 software dcvelopment phasc, 262 63, 301-39 s)'stem integrationphasc,262-63, 301 39 wstemtestphase, 263,29ul,339 43 tenperzture,270-72, 293, 305 testdcfinitionphase, 261-62,29291 lvind clill computation, 282-83 wind direction,277-78,293,305 wind speed,274-77, 284 86,293,306 WG\,I (WaveformGenerationl4odc), 12,1 Whne loop character I/O tunctions,172 tunctionality19 21 indentingtcxt,21,{ asinfiniteloop,3 \4rhite space,,l Wind chill computation,282 83 Wind d;rection,277-78,293,305 W ind specd,271-77, 284 86, 293,306 Word Align FLASH Struct Members option,219

C language for AVR from Atmel AVR Barnet

Related documents

Products

Support

C language for AVR from Atmel AVR Barnet

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib