36 Rockwell Automation Publication 1789-UM002K-EN-P - January 2015
Chapter 2 What is the SoftLogix System?
Determining Programs
Each program contains program tags, a main executable routine, other routines,
and an optional fault routine. Each task can schedule as many as 100 programs
(including equipment phases).
The scheduled programs within a task execute to completion from first to last.
Programs that are not attached to any task appear as unscheduled programs.
You must specify (schedule) a program within a task before the controller can
scan the program.
Table 2 - Task Execution Order for Application with Periodic Tasks and Continuous Task
Task Priority Level Task Type Actual Execution Time Worst Case
Execution Time
1 1 20 ms periodic task 2 ms 2 ms
2 2 10 ms periodic task 4 ms 6 ms
N/A None (lowest) Continuous task 25 ms 35 ms
N/A None Dwell time 10 ms 14 ms
Task 1
Task 2
Continuous
Tas k
Dwell
Time
Task Description
A The highest priority task interrupts all lower priority tasks.
B A lower priority task can be interrupted multiple times by a higher priority task.
C The continuous task runs at the lowest priority and is interrupted by all other tasks.
D The dwell time starts when the continuous task completes. The dwell time does not affect periodic tasks.
Periodic tasks execute as scheduled, regardless of the dwell time.
E The continuous tasks restart, when the dwell time completes, unless a higher priority task is running.
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