How to implement a software watchdog

FAQ #101285

With an activated software watchdog the processor monitors itself and restarts the PCD in the event of a malfunction or a loop.


Description (extract from the hardware manual)
The hardware watchdog provides maximum security. However, for non-critical applications, a software watchdog may be suffcient, whereby the processor monitors itself and the CPU is restarted in the event of a malfunction or a loop.
The core of the software watchdog is the instruction SYSWR K 1000. When this is first issued, the software watchdog function is activated. This instruction must then be issued at least every 200 ms, or the watchdog will trigger and restart the controller.


  • Placing a "Watchdog"-FBox in a FUPLA-file is the easiest solution:
  • Instead of using the FBox it is possible calling the Software Watchdog in IL (using the instruction SYSWR K 1000)




PCD1 / _Firmware Classic

PCD2 / _Firmware Classic

PCD3 / _Firmware Classic

Last update: 29.05.2015 00:47

First release: 21.08.2009 11:58

Views: 29313

The requested software / document is no longer marketed by Saia-Burgess Controls AG and without technical support. It is an older software version which can be operated only on certain now no longer commercially available products.