Rockwell Automation Logix5000 Controllers Tasks, Programs, and Routines Programming Manual - Manual (Page 35)

Chapter 2
Manage event tasks
An event task, if configured correctly, interrupts all other tasks for the minimum
amount of time required to respond to the event.
This section describes how to set up event tasks and lists considerations, such as a
higher priority task, that can affect the execution of an event task.
Each event task requires a specific trigger that defines when the task is to run. The
following table reviews some of these triggers.
To trigger an event task when Use this trigger With these considerations
Digital input turns On or Off Module Input Data State
Change • Only one input module can trigger a specific event task.
• The input module triggers the event task based on the change of state (COS) configuration for
the module. The COS configuration defines which points prompt the module to produce data if
they turn On or Off. This production of data (due to COS) triggers the event task.
• Typically, enable COS for only one point on the module. If you enable COS for multiple points, a
task overlap of the event task may occur.
Analog module samples data Module Input Data State
Change
• Only one input module can trigger a specific event task.
• The analog module triggers the event task after each real time sample (RTS) of the channels.
• All the channels of the module use the same RTS.
Controller gets new data via a consumed tag Consumed Tag • Only one consumed can trigger a specific event task.
• Typically, use an IOT instruction in the producing controller to signal the production of new data.
The IOT instruction sets an event trigger in the producing tag. This trigger passes to the
consumed tag and triggers the event task.
• When a consumed tag triggers an event task, the event task waits for all the data to arrive
before the event task runs.
Registration input for an axis turns On (or Off) Axis Registration
1 or 2
• For the registration input to trigger the event task, first run a Motion Arm Registration (MAR)
instruction. This lets the axis detect the registration input and in turn trigger the event task.
• Once the registration input triggers the event task, run the MAR instruction again to re-arm the
axis for the next registration input.
• If the scan time of your normal logic is not fast enough to re-arm the axis for the next
registration input, consider placing the MAR instruction within the event task.
Axis reaches the position that is defined as the
watch point Axis Watch • For the registration input to trigger the event task, first run a Motion Arm Watch (MAW)
instruction. This lets the axis detect the watch position and in turn trigger the event task.
• Once the watch position triggers the event task, run the MAW instruction again to re-arm the
axis for the next watch position.
• If the scan time of your normal logic is not fast enough to re-arm the axis for the next watch
position, consider placing the MAW instruction within the event task.
Introduction
Choose the trigger for an
event task
Rockwell Automation Publication 1756-PM005-EN-P - October 2014 35