Watchdog (Wd) - Siemens SIMATIC PC 670 Equipment Manual

Hardware Information
7.4.4

Watchdog (WD)

Function
The watchdog monitors the execution of a program. The purpose of the WD is to
report a program crashing to the user by means of different reactions.
After switching on the computing unit or after a HW-RESET (cold start) the
watchdog remains in standby, i.e. no WD reaction is activated and the RUN-LED
remains switched off. If the watchdog is activated (by driver or SOM program) the
Run LED is green.
WD-Reaktionen
If the WD is not retriggered within the set time (by driver or SOM program), the
following reactions are triggered:
RUN LED switches from green to red
Acknowledge WD
Initiate reset on the computing unit
IRQ an die Rechnereinheit absetzen
SOM application is displayed
The reactions you want to have triggered can be set by drivers or the SOM
program.
WD monitoring times TWD
The monitoring times can be adjusted in increments of one second over the range
from 3 to 255 seconds.
Note
If the watchdog time is modified after the watchdog has been activated – in other
words, while the watchdog is running – the watchdog will be retriggered as a
result!
7-8
Reaction
Panel PC 670 Computing Unit, Equipment Manual
Release 04/02
Options
Always
Always
Adjustable
Adjustable
Adjustable