Operators in ST

Operators execute operations and provide functionality, such as addition. The operators combine the operands to form expressions.

Possible operators

No.

Description of operation:

symbol

Examples

Precedence

Corresponding
IEC-block

1

parentheses:

(expression)

A + (B / C)

(A + B) / C

A / (B + C)

12 (highest)


2

call of function or call of a method, if there is a return value:

identifier (parameter list)

ABS(A)

ADD(X,Y)

11


3

dereference

^

Details: see under "Declaration of reference variables (incl. assignments to them)"

R^

10


4

negation:

–

–A

9


5

unary plus:

+

+B

9


6

complement:

NOT

NOT C

9

NOT block

7

exponentiation:

**

A ** B

B ** B

8

EXPT block

8

multiply:

*

A * B

7

MUL block

9

divide:

/

A / B

A / B / D

7

DIV block

10

modulo:

MOD

A MOD B

7

MOD block

11

add:

+

A + B

A + B + C

6

ADD block

12

subtract:

–

A – B

A – B – C

6

SUB block

13

comparison:

<, >, <=, >=

A < B

5

LT block ,
GT block ,
LE block ,
GE block

14

equality:

=

A = B

A = B & B = C

4

EQ block

15

inequality:

<>

A <> B

4

NE block

16a

Boolean AND:

&

A & B

A & B & C

3

AND block

16b

Boolean AND:

AND

A AND B

3

AND block

17

Boolean exclusive OR:

XOR

A XOR B

2

XOR block

18

Boolean OR:

OR

A OR B

1 (lowest)

OR block

Notes:

  • Operators can be →overloaded.

  • Only the following operators can be applied to the datatypes STRING and CHAR: =, <>, <, >, <=, >=

    Deviation from IEC-standard

    The operators for comparison <, >, <=, >= are evaluated with a higher precedence than the operator for equality = and the operators for inequality <>.
    This evaluation is a deviation from the →IEC-standard (edition 3.0) "Table 71 – Operators of the ST language". The table specifies that these operators are of the same precedence.
    However, the evaluation of these operators in logi.CAD 3 is done in accordance with the specifications of the IEC-standard (Edition 3.0) "Annex A Formal specification of the languages elements, Table 71 - 72 - Language Structured Text (ST)". These specifications are also in accordance with the preceding IEC-standard (2nd Edition) "Table 55 - Operators of the ST language".

  • Only the equality operator = and the inequality operator <> can be applied to declared variables based on an →interface and NULL.

    Comparing variables based on an interface or of such a variable with NULL
    interface_variable_1 = interface_variable_2
    interface_variable_1 = NULL
    NULL = interface_variable_2

  • The column "Corresponding IEC-block" informs which operator returns the same results as the corresponding IEC-block. The condition is that the operator works with the same data as the IEC-block. Example: Expression x+y for the addition has a behavior identical to this call of the ADD block: ADD(x,y)Observe: If the block description contains the warnung " No check of invalid connections ", this warnung also applies to the corresponding ST-operator. This warning looks like this (or it is simular to it):

    No check of invalid connections

    For some blocks, invalid connections are not checked by logi.CAD 3. Therefore, enter code in your application to detect invalid connections (e.g. IF-statements in the ST-code).

    See "IEC-blocks for the application" for information what the consequences of an invalid connection might be.

    Deviation from IEC-standard

    The "no check of invalid connections" is a deviation from the →IEC-standard that demands an error handling, if the result of the block exceeds the range of values for the output data type. This deviation also applies to the corresponding ST-operator.

  • On other errors (e.g. in case of a division by 0), the value 0 is returned but the output ENO of the embracing →POU is not set to value FALSE (or an equivalent).

  • Mind the correct combination of the →literals/→variables for multiplication, division, addition and subtraction, if the operation is done for literals/variables of data type TIME. Other combinations will be highlighted as faulty.

    operation: symbol

    data type for operand and result

    example

    behavior identical to this block

    multiply: *

    • 1st operand: data type TIME

    • all following operands: data type belonging to →generic data type ANY_NUM

    • result: data type TIME

    T#1m40s * 2 * 5

    MUL_TIME block, with:
    1st operand = IN1, all following operands are handled as IN2 is handled, result = return value

    divide: /

    • 1st operand: data type TIME

    • 2nd operand: data type belonging to ANY_NUM

    • result: data type TIME

    T#1m40s / 2

    DIV_TIME block, with:
    1st operand = IN1, 2nd operand = IN2, result = return value The operator / calculates using the accuracy as entered for the 2nd operand. That means: If the 2nd operand is a REAL value, logi.CAD 3 is using a REAL value for the internal calculation . Compare: DIV_TIME is using LREAL for the internal calculation .

    add: +

    • 1st operand: data type TIME

    • all following operands: data type TIME

    • result: data type TIME

    T#3s + T#4s + T#1s

    ADD_TIME block, with:
    1st operand = IN1, all following operands are handled as IN2 is handled, result = return value

    subtract: -

    • 1st operand: data type TIME
      2nd operand: data type TIME

    • result: data type TIME

    T#4s - T#3s

    SUB_TIME block, with:
    1st operand = IN1, 2nd operand = IN2, result = return value