Allen-Bradley controllogix 1756-L55M12, Руководство пользователя

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Publication 1756-UM001G-EN-P - January 2007
Develop Applications 69
Define Tasks
A task provides scheduling and priority information for a set of one or
more programs. You can configure tasks as continuous, periodic, or
event.
Types of ControlLogix Controller Tasks
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 only appear once in the
Controller Organizer and cannot be shared by multiple tasks.
Specify Task Priorities
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. You can configure periodic tasks to
execute from the lowest priority of 15 up to the highest priority of 1. A
higher priority task will interrupt any lower priority task. The
continuous task has the lowest priority and is always interrupted by a
periodic or event task.
Task Execution Task Type Description
All of the time Continuous 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.
•
At a set interval,
such as every
100 ms
•
Multiple times
within the scan
of your other
logic
Periodic 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...2000
μ
s. 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.
Immediately when
an event occurs Event An event task performs a function only when a specific event (trigger) occurs. The trigger for the event
task can be:
•
a consumed tag trigger.
•
an EVENT instruction.
•
an axis trigger.
•
a motion event trigger.