Products: ACR9600, ACR9630, ACR9640
A task is equivalent to a program plus the information about how the program can be executed. The definition of a task consists of the name, the information about the execution of the task and a POU of type PROGRAM which should be executed in this task.
IEC61131-3 defines 3 tasks types
-Called once whenever interrupt is called
-Called every N milliseconds
-Must finish before restarted
Cyclic (aka Freewheeling)
-Rescheduled immediately when finished
-Default task type in ACR
Task definition and optimization are managed from the Resources Tab of the IEC PLC Browser
Right-click on the controller name to view or change the resource optimization. The default setting of "Size Only" is recommended. Change individual task optimization as needed.
Right-click on an task to view or edit Optimization settings. By default the task will assume the "resource defaults" described above. Also select from:
Changing the task type is also accomplished by a right-click of the program name and selecting properties.
Cyclic Task is the default. Cyclic tasks will run to completion, in the order listed in the Resource list. The order of execution can be changed by right-clicking the program name and selecting MoveUp or MoveDown.
The Priority of a cyclic task indicates how often the task will run
1= every turn
2= every 2nd turn
3= every 3rd turn, etc
A System Timer task will run every "x" milliseconds as designated by the user. The priority determines which System Timer task takes precedence if more than one are called to run at the same time. System timer tasks always have higher priority than cyclic tasks.Cyclic tasks that are interrupted by a timer task will "pause" during the timer task execution, then resume where left off when the timer task is complete
The Time (ms) (aka Periodic task scan period) should be less than the overall time to run the task and should allow for sufficent time to run other tasks. For example, if the Time=10ms and the actual execution time is 9ms then only 1ms is left to run any other tasks. If the execution time exceeds the interrupt Time, the controller will increase the interrupt time accordingly.
The numeric status panel can be used to determine utilization of System Timer tasks.
Interrupt Tasks are the highest priority. There are three types: