Free online RSLogix 5000 - Controllogix 5000 (Studio 5000 logix designer) RSLogix 5000 Tutorial. This one goes over the PAC controller (some call it a 'Controllogix PLC', really it is a Process Automation Controller) programming project and task.
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A control logics project is comprised of tasks that contain programs routines and other elements. Tasks within the project set the execution priority for one or more programs and schedule the program's execution with up to 32 tasks available.
The task are configured to execute ...
At the creation of a new project, the continuous task in RSLogix 5000 is referred to as the main task. The continuous task is executed continuously as long as periodic or event tasks are not being executed. When the continuous task completes a full scan, it restarts immediately.
Periodic tasks perform a function at a specified interval. Configurable time periods range from point 1 milliseconds to 2,000 seconds. Priorities assigned, range from 1 to 15, with 1 being the highest priority, and are necessary for scheduling when multiple tasks are used. Periodic tasks interrupt the continuous task and execute one time returning control to where the previous task left off.
Event task are executed immediately when a specific trigger occurs. A trigger is defined by the user and can be a change of state of an input or specific motion control operations. Event tasks are assigned priorities with the same scale of periodic tasks ranging from 1 to 15. Event tasks interrupt lower priority tasks when a specific trigger occurs and perform the function defined in the program.
Prioritization and scheduling of tasks is demonstrated with a label applicator production line in a RSLogix 5000 video (subscribe while there). For example a continuous task controls the overall machine functions and conveyor control. A periodic task is assigned to execute every 50 milliseconds to update a visual display with current OEE data. To alert the production line of missing labels and event task is configured using a vision sensor. Each time a missed label is triggered the event task is executed, incrementing a counter on the display screen.
In summary tasks are executed one at a time depending on their priority and only one task is continuous.