Allen-Bradley 1756-L63XT, User Manual

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Rockwell Automation Publication 1756-UM001O-EN-P - October 2014 151
Develop Applications Chapter 10
Task Priority
Each task in the controller has a priority level. The operating system uses the
priority level to determine which task to execute when multiple tasks are
triggered. A higher priority task interrupts any lower priority task. The
continuous task has the lowest priority and a periodic or event task interrupts it.
You can configure periodic and event tasks to execute from the lowest priority of
15 up to the highest priority of 1. Configure the task priority by using the Task
Properties dialog box.
Figure 31 - Configure Task Priority
Programs
The controller operating system is a preemptive multitasking system that is in
compliance with IEC 1131-3. This system provides the following:
• Programs to group data and logic
• Routines to encapsulate executable code that is written in one
programming language
Each program contains the following:
•
Local Tags
• Parameters
•
A main executable routine
•
Other routines
• An optional fault routine