The Multi-Task System
130
Operating Manual XCA 1100 / XCA 1200
●
Version 12/17
9.5
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
'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 ... Set up”
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 may be that you selected address status with
powerflow when debugging in online mode.
Example
Figure124:
Multi-Task-System,
example for tasks and
watchdogs
In
example 1
the watchdog time of the displayed task is set to 10 ms.
The watchdog time is exceeded in the second cycle by 20 ms. The
execution of the task 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 executed again after
30 ms in the fourth cycle.
