Allen-Bradley 1756-L61 User Manual page 150

Chapter 10 Develop Applications
Table 36 - Task Types and Execution Frequency
Task Type Task Execution
Continuous Constant
Periodic • At a set interval, such as each
100 ms
• Multiple times within the scan
of your other logic
Event Immediately when an event occurs
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A task provides scheduling and priority information for a set of one or more
programs. Configure tasks as continuous, periodic, or event by using the Task
Properties dialog box.
Figure 30 - Configuring the Task Type
Table 36 explains the types of tasks you can configure.
Description
The continuous task runs in the background. Any CPU time that is 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.
A periodic task performs a function at an interval.
• Whenever the time for the periodic task expires, the task interrupts any lower priority tasks, executes once, and 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.
An event task performs a function only when an event (trigger) occurs. The trigger for the event task can be the following:
• Module input data change of state
• A consumed tag trigger
• An EVENT instruction
• An axis trigger
• A motion event trigger
The ControlLogix controller supports up to 32 tasks, only one of which can be
continuous.
A task can have up to 1000 programs, starting with Logix Designer application,
version 24.00.00 and later, each with its own executable routines and program-
scoped tags. Once a task is triggered (activated), the programs that are assigned to
the task execute in the order in which they are grouped. Programs can appear only
once in the Controller Organizer and multiple tasks cannot share them.
Rockwell Automation Publication 1756-UM001O-EN-P - October 2014