The multi-task system
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Operating Manual ProNumeric XCI 600 Version 07/16
9.6
Tasks and watchdogs
Each user-defined task has its own settable watchdog. The watchdog
checks that task execution has been completed by the end of the watchdog
interval. 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 the
'STOP'
state if no other actions were programmed. An entry is also made in the
error catalogue. The watchdog time starts when the task is ready to execute.
The watchdog interval is defined in the
“Task ... Settings”
dialog in
MULTIPROG.
Note
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 behaviour may be that you selected address status
with powerflow when debugging in online mode.
Example
Figure 81:
Multi-Task System,
Example for tasks and
watchdogs
In
example 1
the watchdog time of the displayed task is set to 10 ms. In the
figure, the watchdog time is exceeded in the second cycle after 20 ms. Task
execution is interrupted and the "Watchdog" system task is called.
In
example 2
the watchdog time is set to 20 ms. For this reason, it does not
address the time overrun of the task in the second cycle. The task is only
interrupted for the next cycle, and is performed again at 30 ms in the fourth
cycle.
