2
CHAPTER
to MicroProcessorIntroduction
BasedControl
OBJECTIVES
After studying this chaptet you shouldbe able to:
. Unalerstandwhat a microprocessoris. what it does, and how it works.
. Understandthe conceprsof RAM and ROM computermemory and how
via the addressanddatabuses
memoryis accessed
. Understandhow parallel and serial data intedaces work.
. Perform relevant calculationspertaining to analog-to-digital converte$ and
digital-to analog converters.
. Understandthe principles of digilal controller software.
. Recognizeand describethe characteristicsof the various types of available
digital controllefi, that is, micrccontrollers,single-boardcomputers,programmablelogic conoollen, and pe$onal computers.
INTRODUCTION
The digital integratedcircuit (IC) called a microprccessor lFigure 2.1(a)l' hasushered
in a whole new erafor control systemselectronics This revolution has occtmedbecausei
bringsthe fleribilil) ol pfogramcon(rolandrhecomiutarional
rhemicroprocessor
po*er of i iirmputer to beai ciii any problem.iAutomatic co rol applications are pafofthis technology'andmicroprocessor-based
ticularly well suitedto takeaalvantage
confo] systemsarerapidlyreplacingmanyolder controlsystemsbasedon analogcircontlollen
relays,One ofthe first microprocessor-bas€d
cuits or electromechanical
(PLC),
pogrammable
logic
conrroller
was
the
applications
for
control
madespecifically
itself
by
12.
A
microprocessor
in
Chapter
chapter
and
which is discussedlaterin this
circuits
are
input/output
as
memory
and
is not a computer; additional componentssuch
1(b)],
which
is
2
rcquirealto make it opemtional.Howevet tbe microcontroller lFigure
26
CHAPTER2
Figure2.1
(a) Microprocassor
Mlcfocontrollgr
CPU
(microprocessor)
(b) Microcohtroller
doeJcontainall the computerfunctionson a sina closerelativeof the microprocessor,
lack someof $e po$er and speedof the ne\ er mjcroprocessle IC, MicroconLrollers
Inosl'u calleJ
io,t Urt 'f,.rr compcclrre*i' idedlfor mrn) controlJpp'icrtron\:
suchas vendingmacbines,arereallyusingnicroLlevices,
micioorocessor-conirolled
designin control
contrJlle6.Somespecificroasonsfor usinga digitalr'microprocessor
systemsarethe following:
. Low level siSnalsfrom sensors,oncoconvertedlo digital' canbe transmittedlong
distancesvirtuallyerorjree.
'lralegie'
. A microproce..or
canec'il) h"ndlecomplerc"lculalion\andconlrol
. tonrr.irnt..utyi.rvcilablelokeeplmclolpardmeterqin\lo$nroting'y'lem
. irroininn o".onior srategy is easyby loading in a new program;no hardware
changesare requfeo.
. Micriprocessor baseticontrollersare more easily connectedto the computernetwork
andreadcur_
within an organization This allows designeff to enterprogram changes
rcnr\)slemslalusrromlheirJe'krermr'lrl'
ro tvl!891899E9998!49E!!9!fB9!
rNrRoDUCloN
27
In this chapter,we will presentthe basic conceptsof a microprccessor--and
syslem-applicamicrocontrolle;basedsystemwith particularemphasison control
the
restof the text
make
to
but
enough
tions.It is by no meansan in-depthtreatment,
moremeaningful,
hardware
In the firs-tsectionsofthis chapterthe basicconceptsof microprocessor
(theseconceptsalso apply to microcontrollers)l have
and ooemtionare introduceal
haveat
inctudea*ris materiattecausethe studentof moderncontrol systemsshould
leasta generalknowledgeofhow the nicroprocessorperformsitsjob
2.1INTRODUCTIONTO MICROPROCESSOR
SYSTEMIIARDWARE
unit(CPU)'
units:theceniulprocessing
is madeupof fourbasicfunctional
A computer
unit doestheactualcompuF
(VOl Thecentratprocessing
memoiv.input,andoLrtput
logjcunilandcontrolsections
thearithmetic
innoniit iotoor.a oi l\ o subparls:
andlogic,
(ALU)
performs
$e aclurlnumerical
,iin*" Z.:l-fli. *itrlt.tic logi; unit
ol
reclion
conrol
on
The
and
so
AND. OR
ia)iulationssuchasadditionsubEacdon.
ptogramI
nstructhe
thedataflow' suchasreadingandexecuting
theCPUmanages
handsit overto theALU for protheconfol section
calculations,
re-quire
tions.Ifdata
is theCPU
themjcroprocessor
compulet,
cessing.lna mi;roprocessor_based
Figure2,2
cPU(mlcroProcessor)
r------------------i
Bus
Address
ALU
Outptjt TO
To indicatorc,
Registers
DataBus
ConlrolBus
28
CHAPTER
2
Digital datais in the folm of bits, whereeachbit hasa value of either I or 0. Digital
logic 1 and0 Vdc to represenr
logic 0. Eightbits
circuits suallyuse5 Vdc to represent
handles
togetheris called a byte. A microprocessor
digital datain words, wherea word
may be 8, 16, or 32 bits wide. For example,an 8-bit microprccessor
hasa byte sized
word, with a maxinum decimalvatueof 255. (Computersrepresentnumbersin the
binary numbersJstem;forexample,11111111binary = 255 decimal.)The rightmost
bit in a binarynumberhasthe leastvalue(usually1) andis calledtheleastsignificant
the highestvalueandis calledthe most signiff"
bit (LSB). The leftmostbit represents
cant bit O4SB). The convenion betweenbinary and decimal can be performeddirectly
with mostscientificcalculators
or manuallyusingthe techniqueshownin Example2.1.
To expressvalueslargerthan255,lwo or morewordsareput togetherIn this text, we
areusedunlessotherwisestated,
will assume8 bit microprocessors
Find the decimalvalueof the 8-bit binarynumber
SOLUTJON
LSB
MSB
r28..64:.
32 1 6
,0.rr
I :
1
I
lxl=
I
2x1= 2
4x0= 0
8x0= 0
16x1= 16
32x1= 32
64x0= 0..
1 2 8x 1 = 1 2 8
+
179 decimal
The memory section of the computer is a place where digital data in binafy form
(ls and 0s) are stored.Memory consistsof cellsorganizedin S-bitgroups.Eachbyte
CONTROL
TO MICROPROCESSOR.BASED
INTRODUCTION
29
is given a unique numeric address, which reprcsentsits location just as a sreet adalrcss
representsthe location of a house,Dala are written into memory and read out of memory, basedsolely on thoir address.In a particular memory circuit, the addressesmight
start at 1OO0and run consecutivelyto 2000. Figure 2.3 diagramsa section of memory.
Note that the fiIst byte of datahas a decimal value of 2 (00000010= 2 decinal) and an
addressof 1000.
memory.The first is landomCompute$usuallyhavetwo kinds of addressable
acc€ssmemory (RAJI), which allows the computerto read and write dataat any of its
addresses(it is also calledread/writememory or RWM). Alt datain this t ?e of memory
are lost when the poweris tumed off andis calledvolatile memory (an exceptionis
alesignswhere RAM is kept "alive" with a small battery). The secondtype of memory
is read-only memory (ROM), which is similar to RAM exceptthat new datacannotbe
written in; ali dala in ROM are loadedat the factory and cannotbe changedby the computer This memory does not lose its data when power is tumed off and is called nonvolatile m€mory, Most miooprccessol systemshave both RAM and ROM. RAM is
used for temporary program stomge and as a tempomry scratch-padmemory for the
CPU. ROM is usedto storeprogramsanddatathat needto be alwaysavailable Actually,
many computelsusean EPROM (erasablepro$anrmableread-orilymemory) oi an EEPROM (electdcally erasableprograrnnableROM) insteadof a ROM for long{erm mem
ory. EPROMScan be erasedwith a strongUV light and reproFammed. EEPROMScan
be ensed andrepogrammed electrically.Disk ddvosalso storedigital databut in a form
that must be processedbefore they arc accessibleto the microprocessor.
The inpuuoutput (VO) sectionof the computei allows it to inteface with the ool
side wor1d.The input section is the conduit tbrough which new programsand dataare
rnleredinto the compuler.andLheoutpulsecuonallo\L"lhe compulerlo communicale
its rcsults.An VO interfaceis called a port. An input polt is a circuit that connectsinput
devices to the compuler; examplesof input devicesare keyboards,sensors,and
switches.An oulput polt is a circuit that connectsthe computerto output devlces.
Examples of output devicesare indicator lamps, actuators,and monilors. lnput/oulput
is discussedin more detail in the next seciion
Referring again to Figure 2.2, we seethat the blocks are connectedby thrce lines
labeled adalressbus, databus, aIId control bus The addr€ss buljs a group of wiros that
carries an address(in binary {orm) from the CPU to the memory and VO circuits. The
Fig!re 2.3
Address
1000
1001
1002
1003
1004
Data
00000010
01100100
00000000
01011100
10011010
30
CHAPTER2
hasalreadybeendiscussed,
but you may wonneedfor memoryto receiveaddresses
It tums out that all I/O ports are assignedaddresses
der why VO ports need adalrcsses.
and are treated essentially like memory locatrons by the CPU. The CPU oufputs data
to the outside world by sendilg them to a port address.When the circuitry of the designated output port detectsils assignedaddresson the addressbus, it opensand allows
data to passfrom the databus to whateveris connectedto fhe poIt. There arc two ways
is done.Somemicroprccessorsusewhat is calledmemory-mapped
that yO adalressing
itrpuvoutput, where an VO addressis teated just like anothermemory adalrcss.Other
microprocesson treat VO addressescompletely sepante liom memory addresses,
The dats buqis a group of eight wires that carries the actual numedcal data ftom
place to place within the computer Figure 2.2 showshow the databus interconnectsall
blocks. Data flow in both dircctionson t}le databus. For example,input dataenler
tbrough the input port and proceedtbrough the databus to fte CPU. If the CPU needs
to store thesedata, it will sendthem back through the data bus to memory. Data to be
outputted are sent (by the CPU) through lhe databus to lhe output port. If the databus
connectsto all blocks.how do the dataknow which block to go to? The answeris the
addresssystem. For example, when t]rc CPU sendsdata to memory, it does it in two
steps:First, it puts the destinationmemoryaddresson the addressbus; second,it puts
the dala on the data bus.When the designatedmemory detectsits own address,it
"wakesup" and takesthe datafrom the databus.The otherblocks connectedto the
becausethey were not addressed.
A good anaibuseswill igrore the wholesequence
ogy hereis the phonesystem,wherethe phonenumberis analogousto the memory
of phonesmay be connectedto the syslem,whenyou
address.
Eventhoughthousands
dial a numbe! only the designatedphone iings. The beauty of the bus systemis that it
is expandable.Memory or addressableyO units can be addedto the systemby simply
connectingthemto the buses.
The contml bus (seeFigue 2.2) consistsof timing and event-controlsignalsfrom
the CPU. These signalsare usedto control the dataflow on the databus. For example,
oneof the controlsignalsis the r€ad vrite (RJW)line. This signalinformsthe memory if the CPU wishesio read existing daia out of memoly or write new datainto memory. Non-memory-mappedmachineshave a menory-I/O control li e.Thls signal
info.ms the systemif the cunent dataexchangeinvolves memory or an yO port. In genas arethe addressanddatabuses.
eral,the controlbusis not as standardized
2.2 INTRODUCTIONTO MICROPROCESSOR
OPERATION
The microprccessor works by executing a program of instructions. Creating the prc
gram is similar in concepl to programming in BASIC, C, or any other highlevel com
puter language.Each type of microprocessorhas its own instruction set! which is the
insFuc
set ofcommandsthatit wasdesignedto rccognizeandobey.Microprocessor
CONTROL
TO NIICROPROCESSOR-BASED
INTRODUCTION
3l
tions are very elementaland specific, and it usually takesmore than one to accomplish
what a single, high-level languageinshrction would. Many micmprocessorinstructions
simply move datafrom one place to anotherwithin the computer;othen perform mathematical or iogic operations.Still anothergroup of instructions conllol program flow,
such asjumping forward or backwad in the program Each instruction in the instruc
tion set is assignedits own unique operstion cod€, (which is typically 8 bits long and
refered to as the op,code). The CPU usesthis 8-bit number to identify the instluction.
All microprccessorchave at leastone accumulator lFigure 2.4(a)], which is a dataholding registerin the CPU. The accumulatoractsas a "staging area"for data.It is common for datacoming to the CPU to go fiIst to the accumulatot where it can be operated
on. Similarly,most dataleavingthe CPU exits ftom the accumulator.Mathematical
operationsusually store the result in the accumulator.Ma[y of the instructions involve
the accumulatorin one way or another.
A machine languageprogramis a list of instructions(in op-codeform) for the
microprocessorto follow. Before the program can be executed,it musl first be loaded
sequenliallyinto memory.The op codefor lhe first instructionis loadedat the first
adahesslocation, the op-codefor the secondinstruction is loadednext in line, and so on.
Figure 2.4(b) showsa sectronof memory with a shofi Fogram loadedin. The progmm listing includesthe addrcss,op-code,mnemonic,and a brief explanation.(A
mnemonic is an English abbreviation of an insffuction. A Fogram listing using only
mnemonicsis called assemblylaDguage.)The plogram in Figure 2.4(b) dircctsthe CPU
to get I byte of datafrom input port 01, add I to it, and sendthe result lo outputport 02.
Beforc execution can stat, the addressof the first instruction must be loaded into the
registerthatthe
prcgramcounter,The program counter is a specialaddress-stomge
program,
much like a bookmark. Tbe proCPU usesto keep lrack of where il is in the
gram counter always holds lhe addressof the next instruction to be executed.Oncethe
Figure2.4
CPU
lnstruction
Adr
The CPUuseso
tN 01
Explanation
I Get datafrominputport 01.
INRA
OUT02
Incrsmentaccumulaior.
t Senddatato oulputport 02.
Op Code
00
o1
02
03
04
05
DB
01
3C
D3
02
76
HLT
Hall.
o6
(a)
(b) Examplemicroprocessorprogram
2
CHAPTER
microprocessoris activated,executior of ihe progmm is complelely automatic.The exe
first
cution processis a seriesof fetch-executecycles,wherebythe microprocessor
specific
it.
The
following
are
the
and
then
executes
fiom
memory
fetchesthe instruction
stepsthe microprocessorwould go tkough to executelhe program of Figure 2 4(b):
L The microprccessorf€tchesthe first i talction from memory lt knows whereto
find the instruction becauseits addtessis in the program counter
2- Once in th€ CPU, the op-codeis decodedto seewhich instructionit is, then the
proper hardwareis activatedto executethis instruction. In the exampleprogram of
Figure 2.4(b), the 6I5t instruction(IN 0l) is 2 bt'tes long. The first byte of the instruction is the op-code,telling the CPU to inpul data from a Port. The secondbyte of the
instruction rclls the CPU )v/ri./l po( to read from. Exection of tbis instruction causes
dataftom input port 0l to travel along the databus to the accumulator'AIso, the programcounteradvances
to 02 (theaddressof the next instruction)Executionof the
first instructionis now complete.
3. The next fetch-executecycle stans,this time fetchilg lhe insruction flom address02.
is
so the accumulator
The new instruction(INR A) is "incrementthe accumulator,"
(add l) andthe resultpu! backin lhe accumulasentto theALU to be incremented
of the llextinstruction.
to 03, which is the address
tor The programcounteradvances
from address
this
dme
fetching
the
instruction
cycle stans,
4. The nextfetch-execute
03. The instruction(OUT 02) is executed,causingthe accumulatordatato be sent
to outputpoft 02.
to
5. The final instructionis fetched.It is a "halt," which causesthe microprocessor
ceaseoperadngandgo into a wait mode.
2.3 INTERFACINGTO A MICROPROCESSOR
CONTROLLER
An imporlant pan of any control systemis the link betweenthe controller and the real
world. For a digital controller, dataenter and exit through a parallel inlerface or through
a serial interface. Both data formats are discussednext.
The ParallelInterface
The parallel interface transfer data8 bits (or more) at the sametime, using eight separatewires. It is essentially an extensionof the data bus into th€ outside world. The
parallelinterfaceis idealfor inputtingor outputtingdatafrom devicesthat areeither
on or off. For example,a singlelimitswitch usesonly one inputbit, andan on-offsignal to a motor requrresonly one output bit. these l-bit signals are called logic variabl€s, and eight such signals can be provided from a single (8-bit) port This concept
will be expandedon later in this section.
CONIBQ!
TO I\,IlCROPROCESSOR-BASED
TNTRODUCTTON
33
Figure2.5
Digital
inpul
Yout(analogvollage)
'-9.96V
-ace
to connectto an
thecollrollermayusea paral]elinte
In otberapplicalions,
sucha case,the
DC
motor.
ln
driving
a
variable-speed
analogdevice-for example,
voltage
beforeit
into
an
analog
mustfirstbeconverted
binaryoutputofthe controller
a
digital-toby a specialcircuitcalled
is pefformed
cand vethemotor.Thisoperation
analogconverter
Digital-to-Andog Conveft iotl
Thedigitol"to-analogconverter(DAC)is a circuit thatconvertsa digital wordinto an
theinternalworkings
Ii is notwithinthescopeof thistextto describe
analogvoltage.
pararneters
is appropnate.
ofihe
operating
understanding
olthe DAC,bu!a general
DAC.
The
inputis an8-bit
Figure2.5showstheblockdiagramof a typical8-bit
!o thebinaryinputvalueand
digitalword.Theoutputis a currentthatis proportional
voltage(yrtt must
A
stable
reference
an
op_amp
voltage
with
to
a
be
converted
must
is, for
analog
voltage-that
the
maximum
defines
This
voltage
be suppliedto theDAC.
y,"r.
the
is
00000000,
If
the
inPut
is
essentially
%,,r
a digitalinputof 11111I11,%,,i
ot
theoutputvoltageis a linearpercentage
will beOVdc.Forall valuesin between,
is
(for
the8-bitDAC)
for anydigitalinput
theoutprrtvoltage
V,"rSpecifically,
inpul x Ytul
256
(2.1)
= DAC outputanalogvoltage
%,,,
input = decimalvalueofthe binaryinput
Yd = relerencevoltage to the DAC
Findtheana10011011.
7
34
2
CHAPTER
of digital to analogconversionis resolution.The resAn impoitantconsideration
olution of a DAC is the wo$t caseerror that is introducedwhenconvertirgbetween
digital andanalog.This effor occursbecausedigital wordsczmonly rcpresentdisdete
diagramin Figure2.5.For example,the ma\imum
values,asindicatedby the stair-step
valueofan s-bit numberis 255 decimal,which meansthere:re 255 possible"steps"
ofthe ouQut voltage.The differencebetweenstepsis the valueofthe leastsignjficant
bit (LSB). Becausethe smalleslincrcmentis onestep,the rcsolution(for 8-bitdata)is
but if morc
for manyapplicalions,
This tesolutionis adequate
I part in 255,or 0.39Eo.
is needed.two (ormore) 8 bit portscanbe usedtogether.Two portsprovide16 bils of
data.The maximumdecimalvalueof 16bils is 65,535.Being ableto dividean analog
numberinto 65,535paits meansthat eachpart wiil be much smallel,so we can more
precisely representthat number.
INTRODUCTION
TO MICFOPROCESSOR-BASED
CONTROL
Figurc2.6showsa darasheetfor an8-bi!DAC(DAC08O8).
Thisdevicecomesas
a 16-pinDIP (dualin-linepackage)
andusesanextemalop_anp(suchastheLF 351),
tworcsistors,
anda capacitor
io complete
thecircuit.It rcquires
plusandminuspowe;_
supplyvoltages.Thetimeto completea conversion
is a fast 150ns (nanosecondsl.
(The
circuitshownin Figure2.6hasa y,.rof l0Vdc.)
Figure2.6
for the DAC0808.
an 8-bitdigital-to(courtesyof
coa)
ZlaNahonal
ItrSemlconcfuctor
Digilal'toAnalogConvertels
DAC'0808,
DAO080Z
DAC08(m
&Bit D/AConvoders
Ganerrl Degcriptlon
Th. o^coafi ftier t! .r s.bhhcncrrhicdiirLro
*iol 6nsft, toacl t.dur ne I rur xd. d&ur
130d wli ! cl0tnrtn'.nrv
33dw wirhrEV eprlq. it h|.r.".. N,;..r ti"..]
oomiry ), nqui.d rorrqi 'pprcrror rm rr'jiJri
er. ourN..uifqi L lyr4dry!t Lsgor 2a6rrEr/
263, id.r|{ &udI
of 5.k drrn rO,rO* ;;;.
sbir monoroih(y.^drii{ ry *}ih &6 td.t ourllr
.u'6r or hn rhr a r/A F4tdd &blrkro eur..e
i0' IFEF> 2 nA thi po*ri rupptvtuihB ot +.
DACCoI rn6 n. Ind.o.ndrnr
ot btr .dr rid
.rhrblr u{.ri.tly dnrii d.rr...h.tr.r.,hto o{,
tb .nri.r ru.pryvolrrr. tri!.,
?h. DAClgOg
*tit risre d rc y *$ !eh, TTL
oll or Cirosheicrrdr, Indn rdrcr Dtxmmi
r& {,. Mc1!03/MC
t.03.Fe htdrsrdDord
onr
.. DACoIOo
dtr d.n
ElockandConnqcllor
Dlagrarns
TypicalAppllcatlon
l1
t..;
Foeluros
io.$r
.fd
h&imuh
r Fulrrd.curbnrnndhril rs8 !Y'
. 7 rid &bn &aruv rrit.bl. toACOtOr.
DACOOO6|
r F d r r t i r r l m . rl 5 o r r y D
tnoult r.. TTL nd CMOS
. H{0hrF.d nulirtytht i.p. js {r: g 6A/rn
. Por rclpryeohrt u$: |a.svlo !l6v
. L@ Fsd codu pl o.r !! iw e r5v
36
2
CHAPTER
Analag-to-DisitalCom'ers'n
AIl analog-to-digital cotrv€rter (ADC) is a circuit that convefis an analogvoltage into
a digital wcird.A typical ADC consistsof a single IC with a few support components
Analog{o-digital conversionis a morc complicatedprocess(thanfor the DAC), and
the haralwarorequiressomeconversiontime, which is typically in the microsecond
range.The conversiontime requjreddependson the type ofADC, the appliedclock ftequency,and the number of bits being converted.Figurc 2.7 showsa block diagram for
yin is 0
an 8-bitADC. The input yi" canbe any voltagebetween0 V and yef When
yd
(255
decimal).
the ouQut is 11111111
Vdc, the outputis 00000000;when Vinis
For input voltagesbetvr'een0 and V,er the output increaseslinearly with Vin;therefore,
we candeveloDa simDleratio for theADC:
output_ 255
v;
Vnt
(for 8 bits)
Solvingfor outputgivesthefollowingl
Y" x 255
outp'rt=---
(:2.2)
output = decimal output value of an 8-bit ADC
4" = analog input voltage to the ADC
V*r = ADC referencevoltage
pulseis sentto theADC. TheADC
To startthe conversionptocess,a slat_conversion
then samplestbe analoginput and convertsit to binary.When completed.the ADC activatesthe data-readyoutput. This signal can be usedto ale the computerto lead in the
binary da!a.
Figure2.7
Sla conve|sion
Dala r€ady
Clock
Vn (analogvoltageinput)
Digilal
ouIpul
CONTROL
TO NIICBOPROCESSOB-BASED
INTRODUCTION
Figure 2.8
for lhe ADC0804,
ZNational
ZSemiconductor
37
Analog-tGDigltal
Converters
ADC0803,
ADC08048-BitpP
ADCo8fi,ADC0802,
CompatibleArDConverlers
Corp.)
GengralDsscription
Th. Aoc0301, ADmao?, aDco003, A9€$04.t
ourps m.{ l?L voka$ lcsl
shichU$'60d1''.d@lntiomd
MrcBoBUstu nrid.d
30304 .onbl bu., ird TarsTAr
dlb bB, Th6? A/0' rNE, rikr
r wo*swrrh 2.sv i 1M336)voxan 4irro&
. 0V b 5v .
ros lnpurvonas.r
! 03" n.ndiid widrh?0.pii olP pi.r*
rhe @mmon-dodr 4jcriod
and o
n'lhgvo]bg.rt..l
se inplr ai b. ldjund 10all@ .
anra vohrg.rpr. ro rh3rurr3bi! ol BrcLuuon,
Fgalures
KoySpecifications
Sbitr
!l/4 LsB.r1l? LsB3nd1r LsB
r MTcROBUS{30404.omp*ible
5voc
rop?ot!6liom&iJ|yo'wih
or :ndrot.prn.diuft d !01116 r.c6rc.
TypicalApplicatlons
ConnectlonDiagrams
38
2
CHAPTER
:
.:,i,,
l
asa 20-pin
Figure2.8 showsa alatasheetfof an 8-bitADC (ADC0804) Packaged
an
external
requires
power
and
supply
DIP, this device can operateon a single 5_Vdc
pulse
is
applied
resi;tor and capacitorio completetie ADC circuit The start conversion
i"
ADc
frompin5 (INT-R)Thispanicular
fw:nj,'"'a tm a"" 'iady sisnalcomes
ca;"Ji
be connectedin a free-runningmode whereit perfoms one conversionafterthe
setaI half
otheras fast asit can.Nolice alsothatthe pin labeledV*rD(pin 9) mustbe
rangeot
voltage
analog
for
an
call
olthe ac$al V."r For example,if the requirements
rs
a
converslon
complete
0-5 Vdc, then pin 9 would be setto 2 5 Vdc The time to
the
than
approximately100 $s (micro seconds),making it almost700 times slower
earlier
DAC0808discussed
ACo tol $sten UsingPara el Purts
Figure 2.9 showsa positioncontrolsystemusing a microprocessorbasedconlroller
ports (each
wit"hpara el ports. This pafiicular systemhasone output poll andthreeinput
rn a DAC
dre
convened
oorri^ is o" n aaat "r the oulputpon i' panition(d:six bil'
f|direcrion
'ignal.lhere\en!hbil \pecitre'molor
io proriderte ;nalogmolor-dnve
andthe eighthbitturns on an audioalarmif some
clo'ckwise.O = counlerctockwise)'
The
firsr input port inputs the selpoint data' the sec
emergencysituation is detected.
-bit logical r,aflona iputs ttre ,nOC datafrom the sensol'and the third inputs various I
as two limi!
as
well
ables.ln this case,the systemhas three front-panelswitches
INTRODUCTION
TO I\,4ICROPROCESSOR-BASED
CONTROL
Figure2.9
Analog
'l
Switches1oinput
set pointin binary.
/ Gnd = logic0 \
"-1
t0
CHAPTER
2
switches.The limit switchesareusedasa "backup" to detectit if the loadhasgoneout
of its designaled
range.
Operationofthe systenproceedsas follows:The controllerinputsthe datafrom
port 03 !o determineif the start (or stop) button hasbeen pressed.If the stat button has
beenpressed,thenthe setpoint is readin from port 0 1 andthe digitizedsensordatai s
readin from porl 02. Basedon its controlstraregy,the controlleroulputsto port 00 a
binary word representingthe motor control voltage.This digital data is convertedto an
arulog voltage with the DAC. This entire sequenceis repeatedover and over until lhe
stopbuttonis pushed.
The Serial Intelface
In a s€dal interface, the data are sent I bit after the other on a single wire. There are
a numberof goodreasonsfor doingthis.First,the cablingis simplerbecause
only two
wiresareneeded(at a minimun), thosebeing"data" and"retum."Second.shieldinga
small groupofwires, which is olten necessary
in an electricallynoisyindustdalenvi
ronment,is easie.Third, serialdatacanmakeuseofexisting single-channel
datalines
suchas tije telephonesystem(whichmay requireusinga modem).For thesereasons,
serialdatatransferis usuallyrecommended
for distancesgreaterthan 10-30ft.
Becausedataalwaysexistin a parallelform insidethe computet it mustbe converted to serial databefbrc coming oul the sedal polt. This is accomplishedwith a spe
cial parallel-to-serialconverter IC called a universal asynchronous r€ceiver
transmitt€r (UART). On the otherend ofthe line, a receiyerrnustconvertthe serial
databackinto paralleldala,which is donewilh anotherUART.Figure2.10showsthe
basicserialdatacircuit.
Serialdata.rreclassifiedasbeiDgeithersynchronous
orasynchronous.
S]rchftrrr&r
datd require that the databytes be sent as a group in a "package." It is usedin sophistjcatedcommunication
systemsthatmovea lot of dataandwill not be furtherdiscussed
herc. Arytrchmtnus data tlanslbr is the more conmon (but slower) type of serial trans
fer and a11ows
for individualbytesto be sentwhenne€ded.
Figure2.10
conlroller
Serialdala
Paralleldata
Serial'loparallel
(UART)
INTRODUCTION
TO IVICEOPROCESSOR,BASED
CONTBOL
41
Figure 2.11
I 0 1 1 0 0 1(0w i t h
"*{.!$n*..cuon"o"..";.f
Time
Figure 2. I 1 shows the standardformat for asyncbronous
serial data. First, a stat
bir rs .enl. rhenrhedatarLSB fint,. Lhenc paril)_enorchecUng
bit, andfinall\ rhesroD
Drusr. 5ome vaflalionis alio$ed lo !hi. format.bur bothEar.mitrer
andreceirer mu,r
use the samefomat. The other important Dara
u*"iii",."i
p.,,."."Jilliffi
i:i':1fl'#ffi;1ifl
,,illiliJ:Ji:
Tfl
nrcarryIncorrec(rn mostaase,).Srrnddrdbir rars are J00
6ps , bit\ per secondl,1200
bps.%00 bp.. 14.400bps28.800bps.iJ.600 bps.andj7.000
bp".Se;iat
9l_\-2a00
h rlo\aerrh0nparalJel
rransmi5(ion.
At .]oObps,ir Lalesajmosl
t,ms-lo tran(mil b] le of dara.compared
ro lessrt anu mi.ro,econA
fo, parutiit_
rnr(r\ lhousands
of"ltifie( slowfr Slill.for manyapplications.
pdnicularly
proce.\con_
trol, the longerdata-transfer
timesarcnot a problem,
RS232
In orderto makethe serialinterfacepractical,a setof specifications
calledtheRS,232
sandardv ase,!abtirhed.
Officialty.
fie RS-232
shnaara,pec;nes
*e seriuiLra iru.r_raceDelqeendalalerminalequipmenltDTE) anddala communication
equiDment
(DCE).A commordpplicarion
ot RS2J2 is rheinrerfrce
Uerween
;ta;il;
modem,in whichcasethecomputeris theDTE anathenrodemis Are
DCe tseeFieu;e
2.I2(a)lA modemis a devicetharconveds
digiralAntuintouuOto
ro*, * tf,uiit?"
beftansmitted
overthetelephone
lines.As shownin Figure2.12,theRS_232
intefaca
consistsof sevensignals;theserialalatais senton
dn Z ina receiv"Oonpin:; ifreotfrer
signals,suchas"Requestto send',andClearto send,,,areusedto
confiimthatthetwo
un(sareread)rocommunica(e.
TheRS232skndardspecifie\connector
r\Des.sienal
name...pin
num,bers.
aodvologes.In pracdce.
lhenS_ZlUrtana"ra*" li'rpoL;.?rl
any seial interfaceastongas oneunir acrsas a Dfe anatfreottrer
asa OCil n iwo
DTE units needto interfacewirh eachother-for e*"-pl", a pC ro pC_;s;;;i"j
a
cablecalleda rrullmod€mor crossover
cableis use<].
RS 232is comm."t;;;;;
thecontrolfield whentwo unitsneedto exchangedata_for example,
to conieci a pi
to a local controlunit for thepurposeof downloadingu n"*
ot p.og.u., *_ittuJ
tiatedin Figure2.12(b).
"ont
RS-232serialdatatransferis somewhatmorecomplicatedthanparallel
datatrans
fer, but it offersadvantages
suchas two-wjrecommunications
anda universallv
accepted
inferface.Thehardwareto handleserialdatais standardized,
readityavaitab/.
andreliable.
a
:HAPTER2
=8,;re2.12
RS-232
2
3
5
6
20
7
DCE
2
3
Oaiaset ready
5
6
20
7
Computer
=_
Modem
t'
].,.
4
.]
(a) lnterfacebelweendatatermjnalequipment
(DTE)anddatacommunjcalion
equipmenl(DCE).Serialdalaaretransferred
on pins2 and3;the othersignats
conlrol
COIVport(DTE)
{DCE)
(b)Usingan RS-232seriatcable10connecta pC ro a contrcer
Probably*le most commonuseofsedal datais in networking.
More andmore,net
works are being usedto interconnectall the units and device;in
the conrrolsy;tem.
Network cabling differsdepenalingon the type of Iocal area
network (LAi), but
most usethe generalized
bussysremdiagmmmedin Figure2.13.Typically,eachunit
on the net has a uniqueaddressnumberand also aaa.essaetecti#
ci."riit y' Wfr"n
one unir wantsto talk to anolherunit, ir filst broadcaststhe address
ofth; unit its
wantsto talk to (serially,ofcourse,on the signalwire) andthen sends
lhe data(seri_
CONTROL
TO MICROPROCESSOR-BASED
INTRODUCTION
Figure2.'13
43
intefacemodule
ally), which consistsof somenumberof bytes.All units on the net will receivethe
addiess,but only the inteDdedreceiverwill activateand tben read in the data.The
interface betweenthe network cable and the PC is done through a commercially availableinterfaceexpansioncardcalleda networkinteface card (NIC). Other devices
on the net, such as control units, would require a special interface circuit. which may
bebuilt in or availableas an extemalmodule.Control systemnetworksarediscussed
fufther in Chapter12.
2.4 INTRODUCTIONTO CONTROLLER
PROGRAMMING
It is beyond th€ scopeof this text to presenta detailed discussionof how to program a
micrcprocessor in machine language.Stiil, it is useful to investigatein a geneml way
what the software must do. A digital con oller is a computer operating in real time.
This meansthat tr€ pmSram is running all the time-repeatedLy taking in rhe ne\uest
sensordata and the calculating a new outputfor the actuator.
The basic structure of a controller program is a loop. [n a loop sftucture,the same
sequenceofinstructionsis executedover and over again,and eachpassthroughthe
loop is caliedan iteration, or scafl Figure 2.14 showsa generalizedcontro]lerprc$am, and an explanation of the program follows:
L The program rcads in the set-poinl data (recall that the set point is the desiredposition of the controlled vadable).This data could be rcad in from an input port or ftom
memory.
CHAPTER2
Figure2.14
Read in set Point data
Subtractto get eror ,
Sendoulpulvalue
i nme delay(oflional)
)l
(from a sensor)the actualvalue of the con2. The program diEcts the computerto rcail
rolled variable.
po-tnllo gel lj)e efior
l. The actual dala are subtractedfrom the set
a new aclualorconuol slgnar'
4 Basedon the enor da!4 the compulercalculales
5. The new ouqnrt is sent to ihe actualor'
agarn'
6. The pmgrams looPsback to step I and starts ovel
passdrougb lhe loo! deretmine'
The dme il Lakeslor tbecompuErro exwuteoDe
mte) ll ous rnFrvat rs
-nog.hterval betweeninput readbgs ftnowD as fie sampling
lhe dme
\ariable"is
tay Dotgetan accumtepicnxeol whal tbecontrolled
;..otpr"t
.o
be
loopcan
E\ecudonoffie
o* b"ot"r i I lo;a discussionolatiasingr'
'"r,irl1*
the progmm ln otheriruau-"lfi.*oiuy .p".iryine a laslercompuleror strearnlininS
pause
mighl be in\enedlo.'glve
a
exarnph
anowalt.ru
tioos.thecompulermuslpaLrse
for
a motorto splnoown'
time
lo
aliow
or
un opa-tot,i-" ,o a^t a .ome adjustmeot
is simpl}
dme{elay loopsh rheprogramA time'deia} loop
iift"o 0."" ur-f"..**
'
up
to some
count
to
;i*n*r
loop wherethe computeris instmcted
.i*toilitc,
"pi*i"g
ffirff#iili1Jtr!.:
#:#5*x**t;:l*tli"ffir.*.ffi
-rrtr|
$e clcle dmefor lher)lainloop
f*o t*.ft.*"|D tigure 2.l4).lhe efecl is !o slow
lo someptedeerminedvalue
rale
o.* tiorce marchingof tle sample
i*ri -eti. .Jr",-".
midoprocessor pro_
efficienl
one time, peopte thought that the best and most
r,".; ;;;
il;;;;;
w-ould
h fie prosrammer
languase-lhar
in assemulv
Jirec"uv
(calleo
programs
instructionsToday sophisticaled
Lectly relecrthe mactrinelanguage
BASEDCONTROL
TO I\4ICROPROCESSOR
NTRODUCTION
.rmpiler.!) can conve( a programwdtten in a highlevel language,pdmarily C, into
very efficient machinelanguage.Highlevel languagesuseEngiish-soundingwords and
a set ofpoweful commandsto specil, simpleand complicatedprogrammingoperations witb a mjnimum of instruciions.Using a highlevel languageto write programs
ibr a microprocessorollers big advantages.suchas more compactprogram Listing.ease
documentation.
Also. programswritof wdting equations,andmorecomprehensible
to
run
on
any
model
of microprocessor
can
be
compiled
ten in a high levellanguage
CONTROLLERS
2,5 MICROPROCESSOR.BASED
Single-ChipMicrocomputers(Microcontrollers)
A miooprocessor by itself is not a computer To be functional, the microFocessormust
be connectedto other integraledcircuits thal provide the memory and yO capabiiity.A
microcontrolleris a computeron a singleIC, designedspecificallyfor controlapplicamemory(bothRAM andROM), VO pofts,and
tions.It consistsofa microprocessor,
possibly otherfeaturessuchas timers andADCS/DACS.Having the completecontroller
on a single chip allows the hardwaredesign to be simple and very inexpensive.
Microcontrollers are showing up iDcreasinglyin products as varied as industrial appli
cations.home appliances,andtoys. In suchusesasthese,they al€ cailedembeddedcon'
trollers becausethe controller is locatedphysically in ihe equipmentbeing controlled.
The main dillerence betweenmicroprocessorsand microcontrollers is that microprocessorsare being designedfor usein microcomputerswheregreaterspeedand larger
word size are the driving requirements,whercasmicrocontrollers are evolving toward
reducedchip countby integratiDgmorehdrdwarefunctionson tbe chip. Most control
applicationsdo not needthe 32-bit word sizeand500-MHz (megahertz)speedof the
newermicroprocessors.
Eight or 16bits and I MHz will workjusl fine in manyapplications,dndthe single-chipmicrocontrollercostsmuch less.
andmicroconffollersconcernsthe
Anothef differencebetweenmicroprocessors
tendsto be rich in instructionsdealingwith movinstructionset.The microprocessor
ing datainto and out of memory. The microcontroller has fewer memory-moveinstructions and more bit-handlinginstructions.The reasonfor the lack ofmemory-move
instructionsis that the microcontrollertypically has only a small amountofRAM,
which it usesonly as a "scratchpad."The additionalbit handlinginstructionswere
they are so uselul;n controlsystemapplicalions.For example,in a
includedbecause
control system,eachseparatebit ofa parall€l outpul word might control a different
device,suchas a motoror indicatorlight. The bit-handlinginstructionsallow the soft
ware to tum one device easily on or off without affecting the others.
The Motorola 68HC11is a popularS-bit microcontrollerthat has256 bytesof
RAM, 8K ofROM, and512K bytesofEPROM (seeFigure2.15a).It alsohasfive 8
bit polts with built-in sedaldatatransferandADC capability.Anolhercommon8 bit
/
15
CHAPTEB2
Figure2,15
Elock
,
P6iie.:,1
I--fPAOPA2 PA3-PA6 PA7
PBO PBT
(s6raLport) (o thlADc nph)
Also exlenalAddress
and Dala bus
(a) N4olorola68HC11 microconlroller block diag!am
Also exlernalAddless
afd Databus
(b) lnrel8051 mcrocontroller bLockd agtam
RAORAs
(Canaiso be
ADC inpuls)
PIC 16C72mjcfo coilroller blockdiagram
FBO-FB7
RCO-FC7
( C a na l s ob e
senarpon
& iimer !nlerface)
INTRODUCTION
TO MICROPROCESSOR-BASED
CONTROL
47
microcontrolleris the Intel 8051,which has 128b)'tesof RAM and4K bytesof ROM,
four paralleldatapolts, anda sedalpolt (seeFigue 2.15b).For coffio1 applications,
usuallyare adequate:ROM is usedto storethe control
thesehardwarearrangemenrs
program, and RAM is used as data registers and a "scrafch pad." The VO signal lines
can usuallybe connecteddireclly to the microcontrollerwithout addilionalpo cir
cuiny. Software is typically written in C+ or some other language (including assembly language)and then convertedinto machinelanguagewith a compiler or assembler
prcgram.The machinelanguageprogramwould then be loadedinto the microcon
trolier's ROM or EPROM.
Another popular micloconfoller is the PIC from Microchip Technology.For example, the PICl6Cxx family of 8-bit microcontrollers is a low-cost, versitle product that
hasfound wide acceptance[seeFigure 2.15(c)].Therc are a wide rangeof options,
including ROM, EPROM, EEPROM, ADCS, Timers, and serial ports. The PIC usesa
slightly differcnt architecturefrom the 68HC1i and 8051 in that the ROM (o. EPROM)
that containsthe programconnectsto the CPU with its own l+bit bus, whereasthe iegular databus is 8 bits. Allowing I 4 bits for the program memory meansthat all instnrctions arejust one word long. The devicehasthreeI/O ports,but many ofthe I/O bits
can be used in diflerent ways (such as for an orl/off switch or ADC input), depending
on how they are programmed.
Finally, anotherprcduct calledthe BASIC Stampftom Pamlla.\ Inc. is usually considered a microcontrollet allhough it is actually a very small circuit boad with a few
ICs and pins. The whole circuit board plugs into an IC socket, as though il were an IC
(seeFigure 2.16 ). Wlat makesthe BASIC Siamp somewhatuniqueis that it hasan onboard BASIC program interperater.A program can be written in BASIC on a PC and
tl€n dirccdy downloadedinto the Stamp'sEEPROM through a RS 232 pot. No assembler or compiling operation is required. There are now oiher micrccon[ollers on the
market that can be prograrnmedin BASIC.
In summary, a wide vanety of microcontrollers are available. At the low end are
the 4-bit models, which are morc than adequatefor appliancesand toys. Thesetend to
be large-volume,low-cost applications.Eight-bit microcontrollers (suchas the 68HC11
and 8051 menlionedearlier)are very popularbecause8 bits turn out to be a convenient size for both numericandcharacterdata.At the high end, 16 and32-bit microcontrollers are availablefor control systemsrequiiing sophisticated,high-speed
Figure2.16
BASIC Stamp
nodule(BS2Ic).
.$
2
CHAPTER
avionics,or
calculatingpowerfor suchapplicationsascomplicatedservomechanisms.
processng.
image
Single"BoardComputers
computersbuilt on a
Sitrg€'board computers are off-the-shelf microprocessor_based
butin gensingleprinted-circui!card(Figure2.17).Theycomein manyconfigurations,
suchastheZilog 280, the IntelxS6lamilt the
eraltheyusea standadmicroprocessor
Motorola68000,or a microconlrollerThey alsoincludememoryICs (bothRAM and
RoM),l/O capability,andperhapsspecialinterfacecircuitssuchasADCSorDACS
by major nicroprocessorproduceNsuchas
Single-bodrdcompulersaremanufactured
SomesingleboardcomIntel and Motorolaas well as manyolhersmallercompanies.
of
putersare desjgnedto plug into a PC as an expansioncard.The obviousadvantage
andboard-testing
boardis thatit eliminalesdesign_
usinga rcady mademicroprocessor
time. This is paticularly important in small volume productior or one of kind systems.
ProgrammableLogic Controllers
A programmable logic controller (PLC) is a self containedmicroprocessor-based
unit, designedspecifically to be a controller. The PLC includes an yO sectionthat can
Fig|.lre2.17
..
il !
i!n m!.d I *dr1;r.ir!
"r
,iarrra.
t &91{d..,
CONTROL
TO NI]CROPROCESSOR-BASED
INTRODUCTION
49
intedacedjrectly to suchsystemcomponentsas swiiches,relays,small motors,and
lights. Developedin the late 1960sto replacerelay logic controllers,PLCShave
PLCScomein
motioncontrolapplications.
evolvedto be ableto ha dle sophisticated
varioussizesandcapabilities;Figure2.18 showsa selectionof PLCS.The big difi:er
in this sectlonis thatthe PLC has
encebetweenPLCSandthe otherdevicesdiscussed
power
built
i
o
a packagethat hasbeenruggedi
porls,
and
supply
the microprocessor,
is
zedfof an industrialenvironment.Installation vefy easybecausein manycasesthe
sensorsand actuatorscan be connecteddircctly to the PLC- Once installed, the micrc_
processorprogramis downloadedinto the PLC from somesourcesuchas apersonal
computer.The PLC manufacturerusually supplies software to facilitate the program
ming operation.This softwareallows the userto write a programwith line-byline
instructions,or it can converta relay logic-wiring diagram(ladderdiagram)directly
Figure2.18
(Allen-Bndley
50
CHAPTER2
into a PLC program. Multiple PLCSin a plant can be networked so the individual units
can be monitored and programmedfrom a single station. This is a form of distdbuted
computer control (DCC) discussedin Chaptor 1. PLCs are discussedin detail in
Chapter12.
Personal Computers Usedin Control Systems
The availabilityofrelatively low-cost,off-the-shelfpersonal computers (PCs)has
madethem an attractivealtemativefor small, one-of-kind confol applications.control
system software packagesare commercially available for the PC that run under DOS
and Windows. Theseprcgrams are adaptableand allow the user to tailor the software
to fit the control application,essentiallytuming a PC into a PLC (aithoughnot as
rugged).Most of thesepackagesuseinteractive graphicsto link animation with changing processvalues.Someprogramshaveprovisionsto mathematicallysimulatethe
processbeingcontrolledto help optimizethe controllercoefficients.
A standardPC comeswith €xpansion slofs, which are circuit-cald connecton emanaring frcm he motherbodrd(main board) of the computer.E4)ansion cards plug into
ihese slots and foIm a bridge betweenthe compuier and the outside world. Many dif
ferent types of interface cards are available, such as VO seial and parallel datapors,
Figure2.19
Muiti-function lO boaJd.
includesADC. DAC, and
digital LO. (Coulresyof
OmegaEngineering,Inc.)
INTBODUCTION
TO MICROPROCESSOR,BASED
CONTROL
51
ADCS, DACS,and computer-controlledoutput relays, to name a few Figure 2.19 shows
an example of a'l interface expansioncard.
Histodcally, data-acquisitionand controi functions were kept separate.Controllers
ran the process,and other insfuments measuledand recorded the iesu]t. The concept
of havinga singlePC performbolhtasLs\eem\ logical:afler.rll.the pC cdnuseir.
computingability first as the controllerandthen tabulatesystemperfomancedata.
These data can be siorcd on disk and/or displayed on the moniioi.
A potential problem may arisebecausethe contoller must operatein real time. If a
computeris to control a processandmonitor it at the sametime, the alata-rcduction
process
must not take so long as to interferewith the control duties;a connol rcsponsecan't wait.
One way to overcomethis problem is to divide the control and data-acquisitiontasks
amongmultiple processors,
Using the PC as the mastercomputer,a separatemicroprccessoron an expansionca.d canperfom datacolleclion uninterrupted.one type of
yO controller cardhas slots for threesmallerboads. Thesesmallet boardshavevatious
combilations of analogand digital yO ports and counter-timers.Someboardsare available with solid-staterelays, which can be usedto directly control AC andDC motors.
A rc with tO expansioncardsoften costslessthan a stand-alonecomputedzedcon
tloi system.The cardsdo not needa separuteenclosureand use the pc's power supply,
keyboard for input, and monitor for display.Also, using a standardPC meansthat plogiams canbe developedon anothercompatiblecomputer,eliminating processdowntime.
Numerous manufacturersare selling iugged PCs that can survivo in haish industrial environments.Thesecomputerstypically use a membmne,typekeyboard(the keyboard appearsas one continuoussheetofflexible plastic)and havesealedcasesand
filte$ covering the air vents.Somemodels of thesecomputersare rack mountableand
powerluppl.
\ontainlheiro$ n balter)-backup
SUMMARY
A micrcprocessor is a digital integated circuit that peforms the basic operationsof a
computer.Microprocessonareusede"xtensively
asthe basisof a digikl controller Digital
control systemsare advantageous
becausedigital data can be tmnsferredand storedvirtually error-free,andthe contml stmtegycaDbe changedby simply reprogramming.
A computerconsistsoffourbasic functionalunits:(1) the CPU (microprccessor),
which executesthe programmedinsfuctions andperfoms the calculations;(2) the
memory,which storesihe programand data;(3) input; and (4) output.Inpuvoutpu!
interfaces the computer to ihe outside world. A microprocessor,basedcomputerinterconnectstheseunits with threegroupsof signalscalledbuses.The addressbuscarrjes
the addressofthe datato be processed.
The databus caries the data,andthe con[o]
bus carriostiming and control signals.Computershandle data as groups of binaty bits.
Many microprocessorbasedcontrollers handle data in 8-bit gloups called a byte.
A microprccessorhas a set of instructionsthat it can execute(called ihe instruction
set).Each instruction is identified by a digital code called the operationcode (oP.code).
52
2
CHAPTER
A program consists of a list of ihese op-codesstored in memory Tbe micrqro6(f
automatically fetcheslhe instructions ftom memory and executesthem. one bt oEA digital conrroller may havetwo kinds of data intefaces: paiallel and senal-Tbe
parallel interf-ace
is the most straightforwardsystem,where all 8 bits are sentat fte
sametime on eight sepantewires. In the serial inteface, datais sent 1 bit after the otber
on a single wire. Serial data transfer is better for longei distances
Many control systemsusecomponentsthat require an analogsignalinterface;
therefore, the signals to or from the digital conuoller must be convened with an ADC
(analog-to-digital converter) or a DAC (digital to-analog converter) Both circuits are
avaiiablein IC folm.
The digital controllerprogramhasa siandardformat.First, it readsthe setpoint
thesevaluesto determineihe systemenor Based
andsensorvalues,Thenit subtracts
the
on lhe error value, it next calculates appropriateactuator responsesignal and sends
it out.Thenit loopsbackto the beginningof the progmmandexecutesthe samesetof
instructions over and over,
Microprocessorbasedcontrollerscomein a numberof standardforms.A micro_
memory,and inpuvoutputall on a singlelC. A
controllerincludesa microprocessor,
computet assembled
single-board computer is an off{he-shelf microprocessor_based
programmable
logic controller(PLC) is a selfonto a singleprinled circuit board.A
containedunit specificallydesignedto be a controller.A personalcomputer(PC)is a
generalpurpose,self-containedcomputer;however,with the addilion of interface
expansioncards, a PC becomesa very adaptableand cosFeffectivecontroller.
GLOSSARY
usedin
accumulator A tempomrydigital datastorageregisterin themictoprocessor
operalion\.
dnddatcmoving
mrn) mrlh.rogic.
converter.
ADC Seeanalog-to-digital
the locationof I byle of datain memoryor a spe_
address A numberthatrepresents
port.
cific input/oulput
to memoryandyO
addressbus A groupofsignalscomingfromthemicroprocessor
ports,specifying
theaddress.
ALu Seearithmeticlogicunit.
andlogi
arithmeticlogic unit (ALU) Thepaltof theCPUthatperformsarithmetic
cal opemlions.
ananaanIC) thatcanconvert
converter(ADC)A d€vice(usually
analog-to-digital
log voltageinto its digital binaryequivalent
INTRODUCTIONTOVICROPBOCESSOB-BASEDCOI\TBOL
53
assembly language A computerprogmmwrittenin Drnemonics,
whichareEnglishlike abbrevntions
for machine-code
instruclioft.
baud Therateat whichthe signalstatesarechanging;liequentlyusedto mean"bits
per second,"
bjt Thesmallest
unitof digitaidata,whichhasa valueof 1 or 0.
byte An 8-bitdigitalword.
central processingunit (CPU)Thecentralpan ofa computettheCPUperforms
all calculations
andhandles
thecontlolfunctions
of thecomputer
control bus A groupoftimiDgandcontrolsignalscomingfromthomicroprocessor
to memoryandyo pots.
crossovel cable Sr" null mod€m.
CPU Seec€ntralprocessing
unit.
DAC Seedigital-to-analogconverter.
data bus A groupof signalsgoingto andfrom themicroprccessor,
memory,andVO
ports.Thedatabuscaries theactualdatathat arebeingprocessed.
data communicationequipment(DCE)Oneof twounitsspecified
by theRS-232
(for
standard serialdatatransfer);theDCEis usuallya modem.
dataterminalequipment(DTE)Oneoftwo unitsspecified
by theRS-232
srandard
(for serialdatatransfer).TheDTE is rsually the computer
DCE Seedala communication
equipmenl
digital-to-analogconverter(DAC)A circuitthattranslates
digitaldataintoananalog voltage.
prcgramor datainto a computei(ftom another
download To transfera computer
compu@r),
DTE Seedata terminal equipment.
embeddedconttollei A srnallmicroprocessor-based
contlollerthatis permanendy
installedwid n themachineit is controlling.
expansioncard/slot An expansion
cardis a printedcircuitcardthatplugsinto an
(PC).Theexpansion
expansion
sloton themotherboard
of a porsonal
computer
card
usuallyinterfacesthePCto theoutsideworld.
letch-execute cycle A computercyclewheretheCPUfetchesaninstructionandthen
Inpuvoutput(UO)Dataftomtherealwoddmovingin andoutof a computer
YO S€einput/output.
54
CHAPTER2
thata panicularmicroprccessor
is
instfuction set Thesetofprogramcommands
designed
to recognize
andexecute.
programb€ingexecuted
iteration Onepassthfoughthecomputer
by thedigitalconthe
set+oint
and
sensor
data
and
caiculates
the outputto
troller; eachiteration"reads"
ihe actuator,
LAN Seelocalarcanetwork.
leastsignilicantbit (LSB) Therightrnost
bit of a binarynumberCanalsomeanthe
smallestincrcmentof change.
Iogicalvariable A singledatabit in thosecaseswherea singlebit is usedto rcpresentanon-off switch.motoron-offconrol. andsoon.
with
Iocalareanetwork(LAN) A systenthatallowsmultipleunitsto communicate
(dme
inrerconnecrion
wire.
eachorherall sharing
lhe
LSB s€dleastsignificantbit.
mach,nelanguageThesetof operation
codesthata CPUcanexecute.
storcsdigitaldata.Memorydatais storedas
memory Thepartofthe computerthat
bytes,whereeachbyteis givenanaddress.
memory-mappedinput/outpLrtA systemwherevo portsaretreatedexacdylike
memorylocations,
memory,
and
microcontroller An integrated
circuitthatincludesa microFocessot
inpuroutput;in essence,
a "computeron a chip."
microprocessorA digitalintegmted
circuitthatperformsthebasicoperations
ofa
computerbut rcquiressomesupportintegratedcircuitsto be functional.
most significantbit (MSB)Theleftmostbit in a binarynumber.
mnemonic An Englishlike abbreviationof anopemtioncode.
modem A circuitthatconvertsserialdatafrom diqitalform into tonesthatcanbesent
throughthe telephonesystem.
MSB Seemostsigdficsntbit,
nonvolatlle memory ComputermemorysuchasROMthatwill notloseits datawhen
thepoweris turnedoff.
witheachoiher(rre
null modem A cablethatallowstwoDTEunitsto communicate
RS-232).
to idenoperationcode (op-code)A digitalcodewordusedbythemicioprocessor
tify a particularinsffuction.
parallel intertace A typeofdatainterfacewhere8 bits enterol leavea unitat the
sametime on eisht wircs.
TO ]\iIICROPROC@
INTRODUCTION
PC Seepe$onal computer.
genemlpurpose
self_contained'
personal computer (PC) A microprocessor-based,
computer (usuauy refers to an IBM or compatible computer)
PLC S?eprogrammable logic controller.
port has an
port The pan of a computerwhereI/O data lines are connected;each
address.
registerin a computerthat holds the
program counter A specialaddress-holding
ad&essof the nextinstructionto be executed
programmable logic controller (PLC) A rugged,self containedmicroprocessorbasedcontrollerdesignedspecificallyto be usedin an industrialenvironmenl
RAM Sedrandom-accessmemorY.
a memory
random'access memory (RAM) Sometimescalledread/write memory'
RAM
losesits
ou|
wheredatacanhe written in or read
arrangemenlusingadalresses
contentswhenthe poweris turnedoff.
memory'but it
read-onty memory (ROM) Sirnilarlo IiAM in rhat it is addressable
its dalawhen
comespr;programmedanalcannotbe wilten into; also' it doesnoi lose
the power is turned ofi
to memory
read/write (R/W) line A conlrolsignalthatgoeslrom the microprocessor
thal the dali
reaf time Refersto a comp ter mat rs processinglata at the sametime
by the syslem
are generated
the enor that occursbecausedigital
resolution In digital-toanalogconversion,
canonly havecefain discfetevaiues.
data
ROM Se€read-onlymemory.
standardihat specifiesvoltagelevelsand
RS-232standard A seial datatransmission
device)
signal protocol between a DTE (computer) and a DCE (modem or other
BAV Sesr€ad/write line.
data
sampling rate The timespl3rseconda digiralcontrollerreadsthe sensor
scan Se€iteration.
serial inte{ace
a singlewire.
A type of intedace where data are transferred 1 bit ailer the other on
onlo
computerassembled
single-board computer A premademicroprocessor-based
a singleprinted-cifcuitcard.
56
CHAPTEB?
wherethe computeris givena "do-noth_
time-delay loop A progatrming techDique
to somelargenumtterfor thePurposeof delayingtime'
ing" job suchas_cormtin!
UART Seeuniversalasynchronousr€ceivertratrsmitter'
purpose
inte_
universalasynchronousreceivertransmitter (UART) A special
versa'
and
vice
format
parallel
to
sedal
gratetlcircuit that conve(salatafrom
the
volatile memory ComputermemorysuchasI{AM that wil lose its datawhen
poweris tumedof4'
word A unit of digilal datalhata particularcomputer uses:cornmon\ ord sizesaJe
8. 16.and32birs.
E)(ERCISES
Secaion2.1
and
1. Briefly descdbe the functions of the AIU' confiol unit, CPU momory'
input/oLrtPut.
(Specify
2. V/hat stepsdoes the microprocessortake to rcad data at address 1020?
your
answer')
the actions of the adakessbus and data bus in
bus'
^id
control
bus
brs'
data
d/d/ess
alefine
3. Briefly
num4. Use the methoalshownin Example 2.1 to find the decimal value of the brnary
ber01011101.
the binary
5. Use the methoal shown in Example 2.1 to find the decimal value of
number11011010.
Section 2.2
6. wlat is a microFoce ssor instraction set, aldhow is it different from a high-level
latrguage such as BASIC?
7. A certain nicroprocessor has a simple instruction set shown below'
INSTRUCTIONSET
ExDlaation
Op-code
l{a1t the mrcloprocessol
16
Add next byie to accunmlalorc6t
SubEct lext byte frcm accunulator'
D5*
Itrcrement the accuulato!
3C
Decrerent the accunulator3D
Move lhe nert byte into the accumulator'
3E*
'These ins"flclions
use tuo bli"eE'
aftertheProgramshowllbelowwasrun?
what numberwouldbein theaccumulator
INTRODUCTION
TO lllICROPROCESSOR-BASED
CONTROL
PROGRAIi4
Add"ess
001
002
003
004
005
006
0p-code
3E
05
D6
a2
:c
76
Section2.3
E. Temperaturevaluesfrom -20"F to 120"F arc input data for a micropmcessor
com_
puter Are 8 bits sufEcient?Ifso, what is the resolution?
Explainrhe luncrionol he fo|,owingtparutt?l ljam poft and,"riat dan pon.
l.9.
U . s - e n a t d aal rae\ r n r a r1 2 0 0 b p s u s i n g l h e l o r m a r o f F i g u r e 2 . l l . w i { h o n e s r o
How long wouldit taketo send10OO
bytesofdata?
11, An 8 bir DAC has a referencevoltage of 9 V The binary input
is 00 00. Find
the analogoutputvoltage.
12. The^b-inarydataftom the computerin a cetain application are
expectedto go from
00000000ro or ) 00t | | I I L Thesedaraare|}leinpurof a DAC. The dnalo;
oLbur
rhouldgo 0.5 V find $e DAC reference!otlage nece,.aryLomakerhis
iaoojn
13. An 8-birADChasa rererence
!ottage
of t2 v u"aun-rtoe t"pur j.i tiFi;d
thebinaryoutput.
"r
14. Thebinaryoulpurof anADC shouldhavethe mnge00000000_
11 t 111cone_
spondingto aninput of 0-6V Find thenecessary
rcfetencevoltage.
Section 2,4
15-, U\thatls real-timear!p,'jrg, andis it necessary
for controlsystems?
16. De.cribedrebdsic.leps
in a conrolprogram
\can(toopj.
| /. Ar (omeporntjn lheprogram
il js de\iredto harethecompuler
wait5 ! lor an
operalor
re.pon\e.How\ ouldrhisdelaybeaccomplished
in
softwarel
_^
t6. A program
conrains
150jnsFucdonq.
andl})eaterage
e\ecuiion
rimeperinstruc_
tionis 2 ps.Findthesample
rateof thisprogam.
Section 2,5
19. What]s a micmcontroller,ar,d\that arc somediffercncesbetween
a micrccon_
troller anda microptocessot?
20. What is a programmable toeic controller?
You \vant to use a personalcomputer to contlol a simple robot arm.
The arm has
two Joinls, an elbow and a wrist. Eachjoint has a DC motor and a posirion
sensor
that outpursa DC votrage.you atreaalyhavea ,'plain vani[a,,pC;make
a lisr of
what you would need to acquire to make this svstem work.
22. Compareand conrrasrfie following:a ,fli roprocesror.a nicmconrmller,
a pro.
grammable logic contfoller, anda personal computer.