General

BME P58 •0•0 processors can execute single-task and multi-task applications. Unlike a single-task application, which only executes master tasks, a multi-task application.defines the task execution priorities.

Master Task

The master task represents the application program’s main task. You can choose from the following MAST task execution modes:

  • Cyclical (default setup): Execution cycles are performed in sequence, one after the other.

  • Periodical: A new cycle is started periodically, according to a user-defined time period (1 - 255 ms).

    If the execution time is longer than the period configured by the user, the bit %S19 is set to 1, and a new cycle is launched.

The following illustration shows the cyclical execution of the MAST task:

The following illustration shows the periodical execution of the MAST task:

Both MAST task cycle modes are controlled by a watchdog.

The watchdog is triggered if the MAST task execution time is longer than the maximum period defined in the configuration, and causes a software error. The application then goes into HALT status, and the bit %S11 is set to 1 (the user must reset it to 0).

The watchdog value (%SW11) may be configured between 10 ms and 1,500 ms (default value: 250 ms).

NOTE: Configuring the watchdog to a value that is less than the period is not allowed.

In periodical operating mode, an additional check detects when a period has been exceeded. The PLC will not switch off if the period overrun remains less than the watchdog value.

Bit %S19 signals a period overrun. It is set to 1 by the system when the cycle time becomes longer than the task period. Cyclical execution then replaces periodical execution.

The MAST task can be checked with the following system bits and system words:

System Object

Description

%SW0

MAST task period

%S30

Activation of the master task

%S11

Watchdog default

%S19

Period exceeded

%SW27

Last cycle overhead time (in ms)

%SW28

Longest overhead time (in ms)

%SW29

Shortest overhead time (in ms)

%SW30

Last cycle execution time (in ms)

%SW31

Longest cycle execution time (in ms)

%SW32

Shortest cycle execution time (in ms)

Fast Task

The FAST task is for periodical processing and processing over short durations.

FAST task execution is periodical and must be quick so that no lower priority tasks overrun. The FAST task period can be configured (1 - 255 ms). The FAST task execution principle is the same as for periodical execution of the master task.

The FAST task can be checked with the following system bits and system words:

System Object

Description

%SW1

FAST task period

%S31

Activation of the fast task

%S11

Watchdog default

%S19

Period exceeded

%SW33

Last cycle execution time (in ms)

%SW34

Longest cycle execution time (in ms)

%SW35

Shortest cycle execution time (in ms)

Event Tasks

With event processing, the application program’s reaction time can be reduced for events originating from:

  • input/output modules (EVTi blocks)

  • events timers (TIMERi blocks)

Event processing execution is asynchronous. The occurrence of an event reroutes the application program towards the process associated with the input/output channel, or to the event timer that caused the event.

Event tasks can be checked with the following system bits and system words:

System Object

Description

%S38

Activation of events processing

%S39

Saturation of the event signal management stack.

%SW48

Number of IO events and telegram processes executed

NOTE: TELEGRAM is available only for PREMIUM (not on Quantum neither M340)

Single Task Execution

A single-task application program is associated with one task; the MAST task.

The following diagram shows a single-task application’s execution cycle:

Multi-Task Execution

The following diagram shows the level of priority of the tasks in a multi-task structure:

The following diagram shows the execution of tasks in a multi-task structure: