Programming manual M238 | 3 MB - BERGER - POSITEC

Task Types
Introduction
Cyclic Task
Tasks
The following section describes the various task types available for your program,
along with a description of the task type characteristics.
A Cyclic task is assigned a fixed cycle time using the Interval setting in the Type
section of Configuration sub-tab for that task. Each Cyclic task type executes as
follows:
1. Read Inputs: The physical input states are written to the %I input memory
variables and other system operations are executed.
2. Task Processing: The user code (POU, etc.) defined in the task is processed.
The %Q output memory variables are updated according to your application
program instructions but not yet written to the physical outputs during this
operation.
3. Write Outputs: The %Q output memory variables are modified with any output
forcing that has been defined; however, the writing of the physical outputs
depends upon the type of output and instructions used.
For more information on defining the Bus cycle task, refer to the CoDeSys part
of the SoMachine online help and Modicon M238 Logic Controller Settings
(see page 69).
For more information on I/O behavior, refer to Controller States Detailed
Description (see page 49).
NOTE: Expansion I/Os are always physically updated by the MAST task.
4. Remaining Interval time: The controller OS carries out system processing and
any other lower priority tasks.
NOTE: If you define too short a period for a cyclic task, it will repeat immediately
after the write of the outputs and without executing other lower priority tasks or any
system processing. This will affect the execution of all tasks and cause the controller
to exceed the system watchdog limits, generating a system watchdog exception.
NOTE: You can get and set the interval of a Cyclic Task by application using the
GetCurrentTaskCycle and SetCurrentTaskCycle function.
EIO0000000384 04/2012 35