Presentation of the Fast Task

General

The fast task is intended for short duration and periodic processing tasks.

The fast task (FAST) 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 fast task is programmed in one of the following languages: LD, FBD, IL or ST.

SFC language cannot be used in the sections of a fast task.

Subroutines are programmed in LD, FBD, IL, or ST language and are called in the task sections.

The execution of the fast task is periodic.

It is higher priority than the master task.

The period of the fast task (FAST) is fixed by configuration, from 1 to 255 ms.

The executed program must however remain short to avoid the overflow of lower-priority tasks.

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

System objects	Description
%SW1	Task period.
%S31	Fast task activation.
%S11	Watchdog error
%S19	Period overrun.
%SW33	Execution time (in ms) of the last cycle.
%SW34	Execution time (in ms) of the longest cycle.
%SW35	Execution time (in ms) of the shortest cycle.