Lenze DDS v2.3 - Manual (Page 42)

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Programming languages
4-4
l
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 in loops (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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