Functions (FUN) are Program Organization Units (POUs) that upon execution deliver a data element as a result and any number of output values of the classes VAR_OUTPUT and VAR_IN_OUT. By specifying the result type VOID the function has no result.
They can also access global variables via VAR_EXTERNAL, VAR_EXTERNAL_RETAIN or VAR_EXTERNAL_CONSTANT.
Functions do not contain any internal status information, i.e. calling a function with the same input values for the classes VAR_INPUT, VAR_IN_OUT and VAR_EXTERNAL will always yield the same result and the same output values for the classes VAR_OUTPUT, VAR_IN_OUT and VAR_EXTERNAL.
Control FPWIN Pro7 provides two types of functions:
System instructions of the system libraries
IEC standard library
FP library
FP tool library
FP pulsed library
User-defined functions
You can also program your own functions and store them in a user library. The new functions will then be available in all projects in which the user library is installed.
Functions can be written in the following programming languages:
Ladder diagram (LD) or Function block diagram (FBD)
Structured text (ST)
Instruction list (IL)
Functions cannot be assigned to a task as they can only be loaded by a program, function or function block.
A function cannot be called recursively.
The maximum of 5 nested function calls, e.g. Fun1 (Fun2 (Fun3 (Fun4 (Fun5 (x))))), may not be exceeded.
Except for ST or IL functions without formal parameters, function results and function outputs can be left unconnected.
When calling a function with formal parameters in the ST editor, the following conditions apply: