Specifications

4-6

4.2 POUs

4.2.2 Program

A program is an element that is stated at the highest level of POU.

Functions, function blocks, and operators are used to edit programs.

Sequence programs executed in a programmable controller CPU are created by programs of

POU.

For a simplest sequence program, only one program needs to be created and registered to a

task in order to be executed in a programmable controller CPU.

Programs can be described in the ST or structured ladder/FBD language.

4.2.3 Functions

Functions and operators are used to edit functions.

Functions can be used by calling them from programs, functions, or function blocks.

Functions always output same processing results for same input values.

By defining simple and independent algorithms that are frequently used, functions can be reused

efficiently.

Functions can be described in the ST or structured ladder/FBD language.

Program

Operator

Function block

Function

Operator

Function