The watchdog monitors the execution of a program. The purpose of the WD is to
notify the user of a program crash through various reactions.
The watchdog is idle when the PC is switched on or after a HW-RESET(cold
restart), i.e., no reaction of the WD will be triggered and the RUN LED is switched
off. If the watchdog is activated (by driver or SOM program) the Run LED is green.
If the WD is not triggered again within the set time (by driver or SOM program), the
following reactions are initiated:
Watchdog LED switches from green to red
Initiate reset of the PC
SOM application is displayed
The reactions which are to be triggered can be parameterized by driver or
WD Monitoring Times TWD
The monitoring times are adjustable in increments of one second in a range from
3 to 255 seconds.
If the watchdog time is changed after the watchdog was activated (i.e., while the
watchdog is running), the watchdog is retriggered!
SIMATIC Box PC 840 Manual