Lenze DDS v2.3 Instrukcja Użytkownika Pobierz pdf (Strona 42)

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Programming languages

4-4

DDS EN 2.3

4.3 Structured text (ST)

Structured text consists of a series of instructions that can be executed as conditioned in very

high-level languages (IF..THEN..ELSE)or inloops (WHILE..DO). An instruction is completed with

a semicolon;.

Example:

IF value < 7 THEN

WHILE value < 8 DO

value := value + 1;

END_WHILE;

END_IF;

4.3.1 Expressions

An expression returns a value on evaluation and consists of operators and operands.

An operand can be

• a constant,

• a variable,

• a function call

• or another expression.

4.3.2 Evaluating expressions

Expressions are evaluated by processing operators following certain priorities. Operators with the

highest priority are processed first followed by operators with the second highest priority and so on,

until all operators are processed. Same-priority operators are processed from left to right.

The following table lists ST operators in the order of their priority.

Operation Symbol Priority (ranking)

Parentheses (Expression) Highest priority

Function call Function name (parameter list)

Exponentiation EXPT

Negation -

Complementation NOT

Multiplication *

Division /

Modulo MOD

Addition +

Subtraction -

Compare <, >, <=, >=

Equal to =

Not equal to <>

Bool AND AND

Bool XOR XOR

Bool OR OR Lowest priority

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