Control logix project is comprised of tasks that contains programs,routines and other element.
Tasks within the project set the execution priority for one or more programs and scheduled programs execution.With up to 32 tasks available they are configured to execute continuous,periodic or event based.
At the creation of a new project the continuous task in RS Logix 5000 is referred to as the main task.
Continuous Task -
The continuous task is executed continuously as long as periodic or event tasks are not being executed. When the continuous task complete a full scan it restarts immediately.
Periodic Task performs a function at a specified interval.Configurable time period range from 0.1 milliseconds to 2000 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 tasks left off.
Event tasks 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 a 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.