Function Blocks

Function blocks are program organization units (POUs) with multiple input and output parameters. These are instantiated meaning local variables of a function block are copied for each instance. When calling a function block in a program, call the instance of the block where the same code is called but the data used is that which has been allocated to the instance. The values of the variables of an instance are stored from one cycle to the other.

Any POU in a project can call function blocks. Function blocks can call functions or other function blocks. The order of appearance of function blocks within their section is not important.

Define the interface of a function block with a type and a unique name for each of its calling (input) parameters or return (output) parameters. Function blocks can have more than one output parameter. The value of a return parameter for a function block differs for the various programming languages.

Move or copy all function blocks to the Programs section and all but the SFC function block to the Functions section. Also move or copy functions and programs, written with languages supported by function blocks, to the Functions section. When moving or copying a program to the Function Blocks section, all local variables defined in the program are converted to function block parameters.

Function blocks within a project and the global library must have unique names within a scope. Function block names and function block parameter names are limited to 128 characters beginning with a letter followed by letters, digits, and single underscores. The last character for a function block name must be a letter or digit; function block names cannot end with an underscore character. Reserved words, defined words, or data types, such as elementary, structures, or arrays are not valid names.

Each instance of IEC 61131-3 or 'C' written function corresponds to data stored in AADvance virtual machine real time database. Do not add new automatic instances of IEC 61131-3 function blocks or of standard 'C' function blocks with or without initial values. Work with function blocks declared in the

Dictionary

to enable online changes.

User 'C' Function Blocks cannot be added.