296 • Common MODBUS functions
Watchdog (Fieldbus failure)
Modular I/O System
ETHERNET TCP/IP
Register address 0x1004
Designation
Minimum current trigger time, WD_AC_TRG_TIME
Access
read / write
Default
0xFFFF
Description
Using this value the current watchdog status can be read. If the watchdog is
triggered, the saved value is compared with the current value. If the current
value is smaller than the saved value, this is replaced by the current value. The
unit is 100 ms/digit. The saved value is changed by writing new values, which
does not affect the watchdog. 0x000 is not permissible.
Register address 0x1005
Designation
Stop watchdog, WD_AC_STOP_MASK
Access
read / write
Default
0x0000
Description
The watchdog is stopped if here the value 0xAAAA is written first, followed
by 0x5555. The watchdog fault reaction is blocked. A watchdog fault is reset
and writing on the process data is possible again.
Register address 0x1006
Designation
While watchdog is running, WD_RUNNING
Access
Read
Default
0x0000
Description
Current watchdog status.
at 0x0: Watchdog not active,
at 0x1: Watchdog active.
Register address 0x1007
Designation
Restart watchdog, WD_RESTART
Access
read / write
Default
0x0001
Description
Writing 0x1 into the register starts the watchdog again.
If the watchdog was stopped before the overrun, it is not restarted.
Register address 0x1008
Designation
Simply stop watchdog WD_AC_STOP_SIMPLE
Access
read / write
Default
0x0000
Description
The watchdog is stopped by writing the value 0x0AA55 or 0X55AA, if it was
already active. The watchdog fault reaction is deactivated. An existing watch-
dog fault is reset and it is possible to write in the watchdog register again.
In all registers the length is 1, i.e. with each access only one word can be writ-
ten or read.