Industrial Automation course

Transcription

1 Industrial Automation course Lesson 7 PLC Structured Text Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 1

2 Introduction The Structured Text is the higher level IEC programming language. As structure it remembers the Fortrand and the Pascal programming languages (maybe you are too young). Each builder customize the language creating a ad-hoc «dialect» (it means that the programs will not be compliant between developing environments of the competitors. We will concentate on the AS dialect. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 2

3 Base structure Each file containing structured text is made of three different programs: Initialization program Cyclic program Exit program N.B.1: it is not always necessary to have the initialization and the exit program. N.B.2: also with the other programming languages of the IEC 61131, in AS, it is possible to define these three types of execution. Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 3

4 Base structure Program start PROGRAM _INIT (* TODO : Add your code here *) PROGRAM _CYCLIC Program type (* TODO : Add your code here *) Comments Program end Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 4

5 Base structure i N.B.: the execution of the _INIT program is done when the PLC is turned on, the execution of the _CYCLIC program happens with the rate, defined in the Task scheduling of the PLC. It means that all the instructions in the _CYCLIC program are executed every cycle! Example PROGRAM_INIT i := 0; PROGRAM _CYCLIC i := i + 1; IF i>=100 THEN i := 0; END_IF; Ciclo Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 5

6 Keywords Keyword ACCESS BIT_CLR BIT_SET BIT_TST EDGE EDGENEG EDGEPOS Meaning Access to a dynamical variable (pointer) A = BIT_CLR(IN, POS) A contains the value of IN with the POS bit cleared (set to 0) A = BIT_SET(IN, POS) A contains the value of IN with the POS bit set (set to 1) Obtain the value of a bit: A := BIT_TST(IN, POS) A contains the POS bit of IN Identifies the edges of the input Identifies the negative edges of the input Identifies the positive edges of the input Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 6

7 Operators Operator ABS ACOS ADR AND ASIN Meaning Absolute value Inverse cosine Variable address Bitwise AND Inverse sine ASR ATAN COS EXP Right N bits shift : A := ASR (IN, N); IN is N bits right shifted, the left part is filled with the sign bit Inverse tangent Cosine Exponential Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 7

8 Operators Operator EXPT LIMIT LN LOG MAX MIN MOD MOVE Meaning Exponentiation: A := EXPT (IN1, IN2); A=IN1 IN2 Limitation: A = LIMIT (MIN, IN, MAX); MIN is the lower limit, MAX upper limit. If IN is less than MIN, the output is MIN. If IN is higher than MAX, the output is MAX. otherwise, the output is IN. Natural logarithm Base-10 logarithm Maximum between two numbers Minimum between two numbers Remainder of the division between USINT, SINT, INT, UINT, UDINT, DINT variables Assign; "A := B;" is equal to "A := MOVE (B);" Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 8

9 Operators Operator MUX NOT OR ROL ROR SEL Meaning Selection: A = MUX (CHOICE, IN1, IN2,... INX) CHOICE defines which of the variables IN1, IN2,... INX is assigned to A Bitwise not Bitwise or Bitwise left rotation: A := ROL (IN, N); IN is N times bitwise left shifted, the left bit is moved on the right side Bitwise right rotation: A := ROR (IN, N); IN is N times bitwise right shifted, the right bit is moved on the left side Binary selection: A := SEL (CHOICE, IN1, IN2); CHOICE must be BOOL. If CHOICE is FALSE, then the out is IN1. Otherwise, the output is IN2 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 9

10 Operators Operatore SHL SHR SIN SIZEOF SQRT TAN TRUNC XOR Significato Bitwise left shift: A := SHL (IN, N); IN is N bits left shifted, the left part is filled with zeros Bitwise right shift: A := SHR (IN, N); IN is N bits right shifted, the right part is filled with zeros Sine Returns the number of byte of the variable (or of the type) Squared root Tangent Return the integer part of the number Bitwise XOR Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 10

11 Structures IF THEN ELSE Pay attention!!! IF <expression1> THEN <instructions_list1> ELSIF <expression2> THEN <instruction_list2>.. ELSE <instruction_listn> END_IF; Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 11

12 Structures IF THEN ELSE PROGRAM _INIT t := 0; Out := 8; Results: Execution cycle Out PROGRAM _CYCLIC IF t < 4 THEN t := t +1; END_IF; IF t < 2 THEN Out := 0; ELSIF t < 2 THEN Out := 1; ELSIF t > 3 THEN Out := 2; ELSE Out := 3; END_IF; Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 12

13 Structures CASE More values CASE <expression> OF <value1> : <instructions_list1> <value2>, <valore2> : <instructions_list2> <value3>..<valore4> : <instructions_list3> ELSE <instructions_list4> END_CASE; Range of values Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 13

14 Structures CASE PROGRAM _INIT t := 0; Out := 8; PROGRAM _CYCLIC IF t < 4 THEN t := t +1; END_IF; CASE t OF 1 : Out := 6; 0, 2 : Out := 1; 3..4 : Out := 2; ELSE Out := 4; END_CASE; Results: Execution cycle Out Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 14

15 Structures FOR Starting value Increment per cycle FOR <variable> := <expression1> TO <expression2> BY <expression3> DO <instructions_list> END_FOR; Final value (included) N.B.: If the increment moves <variable> to a value higher than <expression2> the cycle is stopped Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 15

16 Structures FOR PROGRAM _INIT A := 0; U := 0; What does it calculate? The factorial of the number A, and assigns it to the variable U PROGRAM _CYCLIC U := A; FOR B := A-1 TO 1 BY -1 DO U := U*B; END_FOR; Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 16

17 Structures REPEAT (tail control cycle) REPEAT <instructions_list> UNTIL <expression> END_REPEAT; Pay attention!!! If <expression> is false the repeat is executed, otherwise it exits. It s the opposite of the C while Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 17

18 Structures REPEAT (tail control cycle) PROGRAM _INIT A := 0; B := 0; C := 0; FOR i:=0 TO 7 BY 1 DO U[i] := 0; END_FOR; PROGRAM _CYCLIC B := A; C := 8; FOR i:=0 TO 7 BY 1 DO U[i] := 0; END_FOR; REPEAT C := C - 1; U[C] := (B/REAL_TO_USINT(EXPT(2,C)))>0; B := B - U[C]*REAL_TO_USINT(EXPT(2,C)); UNTIL C<=0 END_REPEAT; What does it calculate? The binary value of the variable A, and it moves the result in the array U Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 18

19 Structures WHILE (head control cycle) WHILE <expression> DO <instructions_list> END_WHILE; Pay attention!!! If <expression> is true the while is executed, otherwise it exits. The same of the C while N.B.: Let s skip the example of this instruction: it is the same of the C code Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 19

20 Additional instructions EXIT: it is equivalent to the break of the C language, it blocks the execution of the cycle in which it is inserted RETURN: it is equivalent to the return of the C language, it blocks the execution of the function, the function block or the program in which it is inserted Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 20

21 Additional instructions EXIT What is the value of U at the end of the execution? PROGRAM _CYCLIC U := 0; FOR A:=0 TO 1 BY 1 DO FOR B:=0 TO 10 BY 1 DO IF B>=6 THEN EXIT; ELSE U := U + 1; END_IF; END_FOR U := U + 1; END_FOR Let s count the cycles: A=0, B=0 U = 1 A=0, B=5 U = 6 A=0, B=5 U = 7 Instr. out from the first for A=1, B=0 U = 8 A=1, B=5 U = 13 A=1, B=5 U = 14 Instr. out from the first for U has the value 14 Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 21

22 Function Block The Function Block is a part of a control code, with defined interface variables to the outside (input, internal and output). A function block is made of a.st file that contains the structured text software. N.B.: Each program contains also a.fun file with all the interfaces of the blocks, the functions, etc Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 22

23 Function Block Example Develop a FB that calculates U = A B (* File ExampleFB.st *) FUNCTION_BLOCK ExampleFB U := A AND NOT B; END_FUNCTION_BLOCK; (* File Example.st *) PROGRAM _INIT PROGRAM _CYCLIC ExFB(A := In1, B := In2); Out := ExFB.U; N.B.: It is necessary to declare in the Example.st variables, the ExFB variable, with type ExampleFB!! Politecnico di Milano Universidad de Monterrey, July 2015, A. L. Cologni 23