160 Rockwell Automation Publication 1756-UM001M-EN-P - February 2012
Chapter 10 Develop Applications
A task provides scheduling and priority information for a set of one or more
programs. Configure tasks as continuous, periodic, or event using the Task
Properties dialog box.
Figure 26 - Configuring the Task Type
This table explains the types of tasks you can configure.
The ControlLogix controller supports up to 32 tasks, only one of which can be
continuous.
A task can have up to 100 separate Programs
, each with its own executable
routines and program-scoped tags. Once a task is triggered (activated), all the
programs assigned to the task execute in the order in which they are grouped.
Programs can appear only once in the Controller Organizer and cannot be shared
by multiple tasks.
Table 41 - Task Types and Execution Frequency
Task Type Task Execution Description
Continuous All of the time The continuous task runs in the background. Any CPU time not allocated to other operations (such as motion,
communication, and other tasks) is used to execute the programs in the continuous task.
• The continuous task runs constantly. When the continuous task completes a full scan, it restarts immediately.
• A project does not require a continuous task. If used, there can be only one continuous task.
Periodic • At a set interval, such as every
100 ms
• Multiple times within the scan
of your other logic
A periodic task performs a function at a specific interval.
• Whenever the time for the periodic task expires, the task interrupts any lower priority tasks, executes once, and then
returns control to where the previous task left off.
• You can configure the time period from 0.1...2,000,000.00 ms. The default is 10 ms. It is also controller and configuration
dependent.
• The performance of a periodic task depends on the type of Logix5000 controller and on the logic in the task.
Event Immediately when an event occurs An event task performs a function only when a specific event (trigger) occurs. The trigger for the event task can be the
following:
• A consumed tag trigger
• An EVENT instruction
• An axis trigger
• A motion event trigger
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