Watchdog timer (watchdog error supervision timer)
Watchdog timer (watchdog error
The watchdog timer is a PLC function internal timer for detecting errors in the hardware or sequence program. Use FR
Configurator2 (Developer). Select the [PC parameter] window, [PC RAS setting] tab, and set the watchdog timer.
PLC RAS setting
Watchdog timer reset
The PLC function resets the watchdog timer before step 0 is executed (after the END processing is executed).
When the PLC function operates normally and the END instruction is executed by the sequence program within the setting
value, the watchdog timer does not output the signal.
When a PLC function hardware failure occurs or if the END instruction of the scan time could not be executed well within
the setting value, the watchdog timer outputs the signal.
Process when the watchdog timer reaches the setting value
If the scan time exceeds the setting value of the watchdog timer, a watchdog timer error occurs and the PLC function is as
• All outputs of the PLC function turn OFF.
• The P.RUN LED blinks.
• SM1 turns on, and an error code is stored in SD0. (Refer to
WDT (Watchdog timer)
10 to 2000 ms
Excess of scan time over setting
results in watchdog timer error.
Watchdog timer resetting