Siemens Simatic 620 - Manual (Page 139)

Hardware Information
7-7
SIMATIC Box PC 620 Manual
A5E00131465-01
7.4.4 Watchdog (WD)
Function
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 start),
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.
WD Reactions
If the WD is not triggered again within the set time (by driver or SOM program), the
following reactions are initiated:
Reaction Option
Watchdog LED switches from green to red always
Acknowledge WD always
Initiate reset of the PC adjustable
SOM application is displayed always
The reactions which are to be triggered can be parameterized by driver or
SOM program.
WD Monitoring Times TWD
The monitoring times are adjustable in increments of one second in a range from
3 to 255 seconds.
Note
If the watchdog time is changed after the watchdog was activated (i.e., while the
watchdog is running), the watchdog is retriggered!