Warning on the use of the Watchdog timer in DL PLCs

[WRT]

Be warned, despite the apparent documentation of the watchdog timer being able to force the PLC mode into program mode if it takes too long to scan (200ms is the default), neither the toggle switch nor the watchdog will help if you program an endless loop.  The watchdog and toggle are only checked at the END of the scan.

So, if your program gets into a death loop, the only way to restore communications or anything is to:
1) switch the toggle to STOP
2) cycle the power to stop the program
3) return the toggle to TERM (typically)