The XCx Multi-Tasking System
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Operating Manual XCx 300 / 500 / 540 Version 09/08
8.5
Tasks and Watchdogs
Each user-defined task has its own settable watchdog.
The watchdog checks that task execution is complete at the end of the
watchdog time. If task execution is not complete at the end of this time
the system task SPG 10 'WATCHDOG' is executed and the PLC
switches to 'STOP' state if no other actions were programmed.An
entry is also made in the error catalog. The watchdog time starts when
the task is ready to execute. The watchdog interval is defined in the
'Task ... einrichten' [Task ... Setup] dialog in MULTIPROG.
If the execution time of the task and the watchdog time are roughly the
same, and the CPU workload is high, the watchdog time may be
exceeded during certain online operating steps.
The reason for this may be that you selected address
status with powerflow when debugging in online mode.
In this example the watchdog time of the displayed task is set to 10
ms. In the figure the task exceeds its watchdog time at 20 ms. If the
watchdog time of the task is set to 20 ms it will next be executed at
30 ms. In this case task execution at 20 ms will be skipped.
