Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manual de usuario descargar pdf (Pagina 87)

Publication 1794-UM001G-EN-P - January 2007

Develop Applications 87

Programmatically Determine if an EVENT Instruction Triggered

aTask

To determine if an EVENT instruction triggered an event task, use a

Get System Value (GSV) instruction to monitor the Status attribute of

the task.

The controller does not clear the bits of the Status attribute once they

are set.

• To use a bit for new status information, you must manually clear

the bit.

• Use a Set System Value (SSV) instruction to set the attribute to a

different value.

Checklist for an EVENT Instruction Task

For more information on using the event task, see Logix5000

Controllers Common Procedures programming manual,

publication 1756-PM001.

Status Attribute of the TASK Object

Attribute: Data Type: Instruction: Description:

Status DINT GSV

SSV

Provides status information about the task. Once the controller sets a bit, you

must manually clear the bit to determine if another fault of that type occurred.

To determine if: Examine this bit:

An EVENT instruction triggered the task (event task

only).

A timeout triggered the task (event task only). 1

An overlap occurred for this task. 2

For this: Make sure you:

q 1. EVENT instruction Use a Trigger Event Task (EVNT) instruction at each point in your logic that you

want to trigger the event task.

q 2. Task priority Configure the event task as the highest priority task.

If a periodic task has a higher priority, the event task may have to wait until the

periodic task is done.

q 3. Number of event tasks Limit the number of event tasks.

Each additional task reduces the processing time that is available for other tasks.

This could cause an overlap.

q 4. Automatic Output Processing For an event task, you can typically disable automatic output processing (default).

This reduces the elapsed time of the task.

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Rockwell-automation 1794-L34 FlexLogix Controller System User Manual Manual de usuario Pagina 87