User-Defined Function Blocks (POU)

The list of programs is completed with User-Defined Function Blocks (UDFBs).

• UDFBs are described using FBD, FFLD, IL Language SFC, ST Language.
  • They can be used as other function blocks in the programs of the application.
  • Input and output parameters plus private variables of a UDFB are declared in the variable editor as local variables of the UDFB.
• There is no restriction when using any operation in a UDFB.
  • A UDFB can call standard functions and function blocks.
• A UDFB can call another UDFB.
  • The called UDFB must be declared before the calling one in the program list.
• A UDFB can have one or more methods.
  • Methods are used to organize and encapsulate functionality within a UDFB by breaking complex logic into smaller, reusable operations.
  • Similar to methods in object-oriented programming, a method is a reusable block of logic that belongs to a specific UDFB and can access the UDFB’s internal data and variables.
  • See Methods (POU).

Each time a UDFB is instantiated, its private variables are duplicated for the declared instance.

• The code of the UDFB is duplicated on each call in parent programs.
• This leads to higher performances at run-time, but consumes code space.
• It is recommended to package small algorithms in UDFBs.
  • Large parts of code must be managed in programs.

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• • A UDFB can have a maximum of 255 input parameters and 255 output parameters.
  • Compiler issue an error message when this limit is exceeded.