Watchdog (Wd) - Siemens SIMATIC RI 45 PIII Series Manual

Motherboard

2.11.4 Watchdog (WD)

Function The watchdog monitors the program execution. The watchdog has the task of
informing the user about different reactions to a program crash.
When you switch on your PC, or when you execute a cold restart
(HW RESET) the watchdog remains in its quiet state, that means that it does
not trigger any reaction and the RUN LEDs remain dark. If the watchdog is
actve, this is indicated by the green RUN LED (per Treiber or
SFC-Programm).
Watchdog
If the watchdog is not triggered within a preset time interval, the following
Reactions
reactions occur:
RUN LED changes from GREEN to RED
Canceling WD
Relay output falls in quiet state (False contact with middle
contact )
Initiating of PC reset
Transmitting IRQ to PC
If an executed watchdog is retriggered, the green LED is illuminated again.
Options are set via the configuration register bits 6 and 7.
Watchdog Monitoring times are set in steps (from 3 to 255) in the configuration register.
Monitoring Times
TWD
In order to secure the recognition of a fail-state from an interrupt-evaluating
unit which is connected to the relay interface, the SafeCard guarantees an
error hold time of at least 500 ms. This also applies if the PC is reset, for
example, after the watchdog has been executed.
Note
If you modify the watchdog time after the watchdog has been activated (that
is during watchdog execution), the watchdog is retriggered.
2-30
Reaction Option
always
always
always
to be set
to be set
RI 45 PIII, Manual
C79000-G7076-C817-01