Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 759)

L-force | PLC Designer
General Editors

DMS 4.1 EN 03/2011 TD29 757
Expressions
An expression is a construction which after its evaluation returns a value This value is
used in instructions.
Expressions are composed of operators, operands and/or assignments. An operand
can be a constant, a variable, a function call or another expression.
Examples:
33 (* constant *)
ivar (* variable *)
fct(a,b,c) (* function call *)
a AND b (* expression *)
(x*y) / z (* expression *)
real_var2 := int_var; (* assignment, see below *)
Valuation of expressions
The evaluation of expression takes place by means of processing the operators
according to certain binding rules. The operator with the strongest binding is
processed first, then the operator with the next strongest binding, etc., until all
operators have been processed.
Operators with equal binding strength are processed from left to right.
Below you find a table of the ST operators in the order of their binding strength:
Operation Symbol Binding strength
Put in parentheses (expression) Strongest binding
Function call Function name
(parameter list)
Exponentiation EXPT
Negate
Building of complements -
NOT
Multiply
Divide
Modulo *
/
MOD
Add
Subtract +
-
Compare <,>,<=,>=
Equal to
Not equal to =
<>
Boolean AND AND
Boolean XOR XOR
Boolean OR OR Weakest binding