4-7
SIMATIC PC RI25/45, Technical Description
C79000-G7076-C808-01
4.4
Watchdog (WD)
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 a0Eh 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 a
0Eh.
If the watchdog is not triggered within a preset time interval, the following
reactions occur:
Reaction
Option
RUN LED changes from GREEN to RED
always
Canceling WD bit in cell base a 0Eh
always
Relay output falls in quiet state
always
Initiating of PC reset
to be set
Transmitting IRQ to PC
to be set
If an executed watchdog is retriggered, the green LED is illuminated again.
Options are set via the configuration register bits 6 and 7.
Monitoring times are set in four steps in the configuration register.
Time
Contents of register base address
+0Eh
Bit 3
Bit 4
TWD1
1 s
0
0
TWD2
2 s
0
1
TWD3
8 s
1
0
TWD4
16 s
1
1
Function
Watchdog
Reactions
Watchdog
Monitoring Times
TWD
Monitoring Module