Watchdog (Wd) - Siemens SIMATIC PC RI25/45 Technical Description

4.4

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 (hardware
reset) the watchdog remains in its quiet state, that means that it does not
trigger any reaction and the RUN LEDs remain dark. The description of the
I/O cell base address +0Eh triggers the watchdog. This is indicated by the
green RUN LED The watchdog status can be checked in bit 1 of the I/O cell
base address + 0Eh.
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 bit in cell base address + 0Eh
Relay output falls in quiet state
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 four steps in the configuration register.
Monitoring Times
TWD
TWD1
TWD2
TWD3
TWD4
SIMATIC PC RI25/45, Technical Description
C79000-G7076-C808-01
Reaction
Time Contents of register base address
+0Eh
Bit 3
1 s 0
2 s 0
8 s 1
16 s 1
Monitoring Module
Option
always
always
always
to be set
to be set
Bit 4
0
1
0
1
4-7