Programming with statement list © Festo Didactic – Training & Consulting
advertisement
Programming with statement list © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 1 / 56 Operands © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 2 / 56 Operands • System identifiers are referred to as operands. • Operands are elements within the controller that can be interrogated or manipulated using program instructions and operators. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 3 / 56 Absolute and symbolic operand The software allows programs to be written using both absolute and symbolic operand. • Examples of absolute operands are : • I0.1 • T1 • O0.4 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 4 / 56 Absolute and symbolic operand Examples of symbolic operands are : • S1 • Timer • Solenoid • Y1 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 5 / 56 Single bit vs multi-bit operand • Single bit operands (SBO) can be evaluated as true/false in the conditional part of the program sentence and can be set/reset in the execution part of the program sentence. • Multi bit operands (MBO) can be tested for value or compared to other multi bit operands in the conditional part of the sentence. • In the executive part of the program sentence, they can be loaded with a value, decremented or incremented, or manipulated via a rich set of arithmetic and logic operators. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 6 / 56 Single bit operand Operand STL Form Syntax Typical example Input I In.n IF I 2.0 Output O On.n IF I 2.0 SET O2.3 Flag F Fn.n IF F 7.16 RESET F9.3 Counter C Cn IF C3 SET C5 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 7 / 56 Multi-bit operand Operand STL Form Syntax Typical example Input word IW Iwn IF (IW3=V 255) Output word OW Own IF (OW2=V80) LOAD V128 TO OW3 Flag word FW FWn IF (FW3=V220) LOAD V21000 TO FW1 Function Unit FU FUn IF (FU32=V16) LOAD FU34 to R60 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 8 / 56 Multi-bit operand Operand STL Form Syntax Typical example Timer Word TW TWn IF (TW2<V 2000) LOAD V1345 TO TW6 Timer Preselect TP TPn IF (TP0<V20) THEN LOAD V500 TO TP4 Counter Word CW CWn IF (CW3<>V50) THEN INC CW5 Counter Preselect CP CPn IF (CP3=V555) LOAD V67 to CP5 Register R RN IF (R60=V21113) LOAD (R53 + R45) TO R32 Error Word EW EW IF (EW AND V15) LOAD V0 TO EW © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 9 / 56 STL program structure © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 10 / 56 STL program structure • The STL language allows the programmer to solve control tasks using simple english statements to describe the desired operation of the controller. • The modular nature of the language allows the programmer to solve complex tasks in an efficient and self-documenting manner. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 11 / 56 STL program structure – element hierarchy Program Step Sentence Conditional part Executive part © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 12 / 56 STL program structure – step inspection • Although the use of the keyword STEP is optional, most STL programs will use the STEP instruction. • The step instruction is used to mark the beginning of a logical block of program code. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 13 / 56 STL program structure – step inspection • Each STL program may contain up to 255 discrete STEPS. • Each step may contain one or more sentences. • Each step may be assigned an optional label or name. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 14 / 56 STL program structure – step inspection • A step label is only required if the respective step will later be assigned as the destination of a jump instruction. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 15 / 56 STL program structure – sentences • The sentence forms the most basic level of program organisation. • Each sentence consists of a conditional part and an executive part. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 16 / 56 STL program structure – conditional part • The conditional part serves to list one or more conditions which are to be evaluated at run time as being either true or false. • This part usually begins with the if keyword and continues with one or more statements that describe the conditions to be evaluated. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 17 / 56 STL program structure – conditional part • If the program conditions are evaluated as true, then any instructions programmed in the executive part of the sentence will be performed. • Examples are: • If I0.1 • If I0.2 and I1.3 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 18 / 56 STL program structure – executive part • It is the section of the sentence where the output is activated if the conditional part is evaluated as true. • Examples are : • THEN SET Y1 • THEN RESET Y2 • THEN JMP TO 10 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 19 / 56 STL program structure – step instruction • Programs that do not use the STEP instruction can be processed in a parallel (scanning) fashion. • Although this type of program execution may be well suited for solving certain types of control tasks, the STL language provides the step instruction which allows programs to be divided into discrete sections (steps) which will be executed independently. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 20 / 56 STL program structure – step instruction In its simplest form, a STEP includes at least one sentence. STEP IF THEN (label) I1.0 SET © Festo Didactic – Training & Consulting If Input 1.0 is active O2.4 then turn on output 2.4 and proceed to the next step. PLC programming 20.12.03 No. 21 / 56 STL program structure – step instruction • It is important to understand that the program will WAIT at this STEP until the conditions are true at which time the actions will be performed. • Only then will the program proceed to the next step. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 22 / 56 STL program structure – programming Single sentence within a step STEP Start IF THEN STEP Stop IF THEN © Festo Didactic – Training & Consulting SET - Label for STEP can be up to 8 alphanumeric I0.0 - Conditional part O0.0 - Execution part RESET I0.1 O0.0 PLC programming 20.12.03 No. 23 / 56 STL program structure – programming • Single sentence within a step • The program will execute the first step, STEP start. • If the condition i0.0 is true, then it will execute the execution part (set O0.0) and proceed to next step, STEP stop • If the condition is false, it will WAIT at STEP start. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 24 / 56 STL program structure – programming Multiple sentence within a step STEP Start IF THEN SET I0.0 - First Sentence O0.0 IF THEN SET I0.1 - Second Sentence O0.1 SET I0.2 - Third Sentence O0.2 RESET RESET RESET I0.1 O0.0 O0.1 O0.2 IF THEN STEP Stop IF THEN © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 25 / 56 STL program structure – programming • Multiple sentence within a step • Sequence of execution • If the conditional part of the first sentence is true, then it will execute the execution part and proceed to second sentence WITHOUT any exception © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 26 / 56 STL program structure – programming • If the conditional part of the second sentence is true, then it will execute the execution part and proceed to third sentence WITHOUT any exception. No waiting at second sentence. • If the conditional part of the third sentence is true, then it will execute the execution part and proceed to next step. If not true, it will proceed to first sentence, second sentence and it will loop within the step. • Generally, only when the last sentence within the step is true, it will proceed to next step. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 27 / 56 STL program structure – programming • If the conditions of a sentence are met, then the programmed actions are executed. • If the conditions of the last (or only) sentence within a step are met, then the programmed actions are executed and the program proceeds to the next step. • If the conditions of a sentence are not met, then the program will move to the next step in the current step. • If the conditions of the last (or only) sentence within a step are not met, then the program will return to the first sentence of the current step. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 28 / 56 STL program structure – influencing program flow In addition to the control structures inherent within the step instruction, several additional STL instructions are available which can be used to influence the execution criteria of program steps and sentences. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 29 / 56 STL program structure – NOP instruction • The NOP instruction may be used in either the conditional or executive part of a sentence. • When used in the conditional part, the NOP instruction is always evaluated as true. • The NOP instruction can be used to cause unconditional execution of a sentence. IF THEN SET © Festo Didactic – Training & Consulting NOP O1.0 This is always True so Output 1.0 will always be turned on when the program reaches here PLC programming 20.12.03 No. 30 / 56 STL program structure – NOP instruction Example of an NOP instruction © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 31 / 56 STEP 50 IF THEN SET I10.0 O2.2 If input 1.0 is active then turn on output 2.2 N AND RESET I3.5 I4.4 O1.2 If input 3.5 is not active and input 4.4 is active then turn off output 1.2 IF THEN SET T3 F0.0 If timer 3 is running then set flag 0.0 IF NOP THEN SET IF THEN © Festo Didactic – Training & Consulting O3.6 In any case, we make sure that the last sentence will always be true Turn on output 3.6, exit and go to next step PLC programming 20.12.03 No. 32 / 56 STL program structure – NOP instruction • In step 50, several conditions were to be checked. • If they were true, the appropriate actions were executed. • However, regardless of whether any or all of the conditions were true, after being checked exactly one time the program would turn on output 3.6 and proceed to the next step. • We have forced the last sentence to be true via the nop instruction. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 33 / 56 STL program structure – NOP instruction • The NOP instruction may also be used in the executive part. Here the NOP is equivalent to “do nothing”. • It is often used when the program is to wait for certain conditions and then proceed to the next step. IF THEN I3.2 NOP © Festo Didactic – Training & Consulting If Input 3.2 is Active Do nothing and go to the next step. PLC programming 20.12.03 No. 34 / 56 STL program structure – jump instruction • The JMP instruction adds the ability of program branching to the STL language. • As an example, we will modify the previous example used for NOP instruction. • It would now be possible to test the conditions of each sentence and if true perform the programmed action and then jump to a designated program step. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 35 / 56 STEP 50 IF THEN SET JMP TO I10.0 O2.2 70 If input 1.0 is active then turn on output 2.2 and jump to step label 70 N AND RESET JMP To I3.5 I4.4 O1.2 6 If input 3.5 is not active and input 4.4 is active then turn off output 1.2 and jump to step label 70 IF THEN SET T3 F0.0 If timer 3 is running then set flag 0.0 IF THEN NOP SET O3.6 Always true, so ... Turn on output 3.6, exit and go to next step IF THEN © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 36 / 56 STL program structure – jump instruction • It can be seen that not only have we altered the program flow, but in addition have established priorities between the sentences. • Sentences 2,3 and 4 will only have the possibility to be processed if sentence 1 is false and therefore not executed. • If sentence 1 is executed, the program will jump to step 70 without ever processing any subsequent sentences in step 50. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 37 / 56 STL program structure – OTHRW instruction • The OTHRW instruction is executed when the last encountered IF clause is evaluated as not true. IF I2.0 If Input 2.0 is active THEN SET O3.3 Turn on output 3.3 OTHRW RESET O4.5 Otherwise turn on output 4.5 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 38 / 56 STL program structure – OTHRW instruction STEP execution with OTHRW (Otherwise) instruction STEP Start IF THEN SET OTHRW RESET - Label for STEP can be up to 8 alphanumeric I0.0 - Conditional part O0.0 - Execution part O0.0 - Execution part STEP Stop IF THEN RESET I0.1 O0.0 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 39 / 56 STL program structure – OTHRW instruction • The program will execute the first step, STEP start. • If the condition i0.0 is true, then it will execute the execution part (set O0.0) and proceed to next step, STEP stop. Otherwise (if not true), it will execute the RESET O0.0 and proceed to next step, STEP stop • In this case, there is no waiting at STEP start, either it executes SET O0.0 or RESET O0.0 and proceed to next step © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 40 / 56 STL instruction summary © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 41 / 56 STL instruction summary The STL language provides the following instructions which allow both simple and complex tasks to be solved quickly and easily. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 42 / 56 STL instruction summary AND Performs a logical AND operation on single or Multibit operands and constants. BID Converts the contents of the Multibit Accumulator from Binary to BCD format. CFM n Begin Execution of a Function Module. CMP n Begin Execution of a Program Module. CPL Produces the two’s compliment of the contents of the multibit accumulator. DEC Decrements a Multibit Operand / Accumulator. DEB Converts the contents of the Multibit Accumulator from BCD to Binary format. EXOR Performs a logical EXOR operation on single or multi operands and constants. IF Keyword marking the beginning of the Conditional part of a sentence. INC Increments a Multibit Operand / Accumulator. INV Produces the one’s compliment of the contents of the multibit accumulator. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 43 / 56 STL instruction summary JMP TO (Step Label) Causes the program to continue execution at the specified Step. LOAD Allows loading specified operands (single or multibit) and constants to either the single or multibit accumulator. NOP A Special instruction which is Always True in the Conditional Part of a sentence. In the Executive Part it is equivalent to “Do nothing”. OR Performs a logical OR operation on single or multibit operands and constants. OTHRW Provides the ability to continue program execution if the Conditional Part of a sentence is False. RESET The Reset instruction is used to change single bit operands to logical “0” status. ROL Rotates Left all bits contained in the Multibit Accumulator by one position. The most significant bit is moved to the least significant bit. ROR Rotates Right all bits contained in the Multibit Accumulator by one position. The most significant bit is moved to the most significant bit. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 44 / 56 STL instruction summary SET The Set instruction is used to change single bit operands to a logical “1” status. SHIFT Performs a Single Bit Swap between a Single Bit Operand and the Single Bit Accumulator. SHL Shifts Left all bits contained in the Multibit Accumulator by one position. The most significant bit is lost, and the least significant bit is filled with a zero (0). SHR Shifts Right all bits contained in the Multibit Accumulator by one position. The most significant bit is lost, and the least significant bit is filled with a zero (0). SWAP Exchanges the high and low order bytes of the Multibit Accumulator. TO Used with the LOAD instruction to specify a destination operand. THEN Keyword marking the beginning of the Executive Part of a sentence. WITH Used to pass parameters with some CFM/CMP instructions. Also used to specify timer clock rates for some PLC models. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 45 / 56 Multitasking © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 46 / 56 Multitasking • Multitasking is the term used for the “simultaneous” execution of a number of different tasks (problems, programs) • Organising the program sections using modular programming techniques. • The PLC program can consist of several parts each of which is a program in its own right. These programs have various functions. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 47 / 56 Multitasking • The advantages of this method of working include clearer program structures and shorter cycle times. • With multitasking it is easy to program several different operating modes and to be able to call them up at any time and to run parallel with the main program. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 48 / 56 Multitasking P0 Main control program P0 is activated automatically when power on © Festo Didactic – Training & Consulting P1 CMP 0 CFM 0 CMP 49 CFM 49 P63 CMP 99 CFM 99 Program ( Multi-Tasking ) Module Program ( Subroutine ) Function modules ( Predefined by Festo ) P2 PLC programming 20.12.03 No. 49 / 56 Multitasking • Multitasking – modules can be activated by the main program / other programs to run concurrently. • P1 to p63 can be activated to run parallel with P0. Hence, a multi-tasking of 64 programs can be achieved. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 50 / 56 Multitasking STEP 10 Then Set O0.0 P0 STEP 20 If I0.0 Then SET P1 STEP 30 Then Reset O0.0 © Festo Didactic – Training & Consulting STEP Start If I0.1 Then Set O0.2 P1 STEP End Then NOP PLC programming 20.12.03 No. 51 / 56 Multitasking – call module program • Sub routine – modules can only be activated by the main program to run as sub-routines. (CMP – call module program) • Command – CMP X THEN CMP x module number x With p1 1st parameter With p2 2nd parameter With p3 3rd parameter With p4 4th parameter © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 52 / 56 Multitasking – call module program STEP 10 Then Set O0.0 P0 STEP 20 If I0.0 Then CMP0 STEP 30 Then Reset O0.0 © Festo Didactic – Training & Consulting STEP Start If I0.1 Then Set O0.2 B0 STEP End Then NOP PLC programming 20.12.03 No. 53 / 56 Multitasking – call function module • Sub routine – modules can only be activated by the main program to run as sub-routines. (CFM – call function module) • Command – CFM X THEN CFM x module number x With p1 1st parameter With p2 2nd parameter With p3 3rd parameter With p4 4th parameter © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 54 / 56 Multitasking – call function module STEP 10 Then Set O0.0 P0 STEP 20 If I0.0 Then CFM 8 With v2 With v6 Function Add (Internal Module) v2 + v6 = v8 F8 Load FU32 To R0 © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 55 / 56 Multitasking - summary When you are doing multitasking: • The sub-program will be activated and will run together with the main program, which will still carry on running. • The programs are running parallel. • When using the CMP (call module program) or CFM (call function module) command, you are activating a sub-routine. • In this case, the main program will stop and stay at that step and the sub-program will be activated. • Only when the sub-program is completed it will jump back to the main program at the point where it left. © Festo Didactic – Training & Consulting PLC programming 20.12.03 No. 56 / 56
