Lenze PLC Designer PLC Designer (R2-x) - Manual (Page 44)

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What is What in PLC Designer
42 DMS 3.2 EN 02/2011 TD29

Calling FUB in FBD (Declaration part as shown above for IL):
In SFC function block calls can only take place in steps.
4.1.7 Program
A program is a POU which returns several values during operation. Programs are
recognized globally throughout the project. All values are retained from the last time
the program was run until the next.
Example of a program
Programs can be called. A program call in a function is not allowed. There are also no
instances of programs.
If a POU calls a program, and if thereby values of the program are changed, then these
changes are retained the next time the program is called, even if the program has
been called from within another POU.
This is different from calling a function block. There only the values in the given
instance of a function block are changed.