Overview of the Program Unit

Program Units are autonomous programming entities (only available for Modicon M580 and M340).

The Program Unit includes:

• Public and local variables

• Sections

  The following programming languages are supported:

  • FBD (Function Block Diagram)

  • LD (Ladder Diagram Language)

  • SFC (Sequential Function Chart) only for sections in Program Unit which belongs to the MAST task

  • IL (Instruction List)

  • ST (Structured Text)

• Animation tables

The Program Units are linked to a task. The same Program Unit cannot belong simultaneously to several tasks.

The sections and Program Units under a task are executed in the order of their programming in the browser window (structure view).

The sections under a Program Unit are executed in the order of their programming in the browser window (structure view).

The identification tags of the instruction lines, the contact networks, and so on, are specific to each section of the Program Unit (no program jump to another section of the same Program Unit is possible).

An execution condition can be associated with one or more Program Units and or sections of Program Units.

Example

The following diagram shows a task structured into Program Units and sections:

The execution order in this MAST task example, starts with ProgramUnit1, continues with Section1 and ends with ProgramUnit2. Inside ProgramUnit2 the execution order is first Section1_P2 then Section2_P1.

Characteristics of a Program Unit

The following table describes the characteristics of a Program Unit: