CJ2 CPU Unit Software User's Manual - CIP ETI

5 Understanding ProgrammingInputInput ON delay time(Interrupt Input Unit retrieval)Ready for nextinterrupt Input Unit retrievalInterrupt task executionI/O interrupt taskinterrupt response timeLadder programexecution timeCyclic taskreturn timeCycle execution task execution(main program)External InterruptsInterrupt processing is performed at the CPU Unit in PLCs containing Special I/O Units or CPU BusUnits. Settings do not have to be made at the CPU Unit unless the program contains an external interrupttask for a particular task number. The Special I/O Unit or CPU Bus Unit must be connected in theCPU Rack to enable external interrupts.Receiving external interrupt tasks is always enabled. The maximum number of tasks is 256 (interrupttask numbers 0 to 255).Example: External Interrupt from a CJ1W-CT021 High-speed Counter UnitCPU UnitCyclic taskSpecifiesexternal interrupttask number andrequestsinterruptprocessing.CJ1W-CT021Data55-2 TasksInterrupt task5-2-3 Interrupt TasksI/O memoryTo communicate to the CPU Unit the status information for the two external control inputs and 32 outputsof this Unit for other than I/O refreshing, set the external control inputs or outputs so that they triggerthe external interrupt task.Precautions for Correct UseDo not use the same number for more than one interrupt task.If an external interrupt task (0 to 255) has the same number as a power OFF task (task 1),scheduled interrupt task (task 2 or 3), or I/O interrupt task (100 to 131), the interrupt task will beexecuted for either interrupt condition (external interrupt or the other interrupt condition). Overhead Time for External Interrupt TasksFor external interrupt tasks, the time until the CPU Unit receives the interrupt signal depends on thetype of Unit or Board (i.e., Special I/O Unit or CJ-series CPU Bus Unit) that requests execution of theexternal interrupt task from the CPU Unit and the service type of the interrupt request. For details,refer to the relevant Unit manual.CJ2 CPU Unit Software User’s Manual5-27