Rockwell Automation 5720 DriveLogix System - Manual (Page 40)

Publication 20D-UM002C-EN-P - November 2003
2-6 What Is DriveLogix?
Using the Event Task The event task is available with DriveLogix controllers using firmware version
12.x or greater. Previously, the only tasks available were the continuous task
and periodic task. However, the event task offers DriveLogix controller users a
task that executes a section of logic immediately when an event occurs.
An event task performs a function only when a specific event (trigger) occurs.
Whenever the trigger for the event task occurs, the event task:
• interrupts any lower priority tasks
• executes one time
• returns control to where the previous task left off
For DriveLogix controller, the event task trigger can only be the EVENT
instruction.
Prioritizing Periodic and Event Tasks
Although a DriveLogix project can contain up to 8 tasks, the controller
executes only one task at a time. If a periodic or event task is triggered while
another task is currently executing, the priority of each task tells the controller
what to do.
The DriveLogix controller has 15 priority levels for its tasks. To assign a
priority to a task, use the guidelines described in Table 2.1.
Table 2.1
If you want: Then Notes:
this task to interrupt another
task Assign a priority number
that is less than (higher
priority) the priority number
of the other task. • A higher priority task
interrupts all lower
priority tasks.
• A higher priority task
can interrupt a lower
priority task multiple
times. another task to interrupt this
task Assign a priority number
that is greater than (lower
priority) the priority number
of the other task.
this task to share controller
time with another task Assign the same priority
number to both tasks. The controller switches back
and forth between each task
and executes each one for
1ms.