General

The master task represents the main task of the application program. It is obligatory and created by default.

Structure

The master task (MAST) is made up of Program Units and/or sections and subroutines.

NOTE: Program Units are only available for Modicon M580 and M340.

Each section of the master task is programmed in the following languages: LD, FBD, IL, ST or SFC.

The subroutines are programmed in LD, FBD, IL, or ST and are called in the task sections.

NOTE: SFC can be used only in the master task sections. The number of sections programmed in SFC is unlimited.

Execution

You can choose the type of master task execution:

  • cyclic (default selection)

  • or periodic (1 to 255 ms)

Control

The master task can be controlled by program, by bits and system words.

System objects

Description

%SW0

Task period.

%S30

Master task activation.

%S11

Watchdog error.

%S19

Period overrun.

%SW27

Number of ms spent in the system during the last Mast cycle.

%SW28

Maximum overhead time (in ms).

%SW29

Minimum overhead time (in ms).

%SW30

Execution time (in ms) of the last cycle.

%SW31

Execution time (in ms) of the longest cycle.

%SW32

Execution time (in ms) of the shortest cycle.