Common MODBUS functions • 295
Watchdog (Fieldbus failure)
Modular I/O System
ETHERNET TCP/IP
Watchdog Register:
The watchdog registers can be addressed in the same way as the described in
MODBUS function codes (read and write). Specify the respective register ad-
dress in place of the address of a module channel.
Register address 0x1000
Designation
Watchdog time, WS_TIME
Access
read / write
Default
0x0000
Description
This register saves the value for time exceeded (Time-out). To be able to start,
the watchdog default value must have a value which is not equal to zero. The
time is set as a multiple of 100 ms, 0x0009 means a time out time of 0.9 s.
This value cannot be changed when the watchdog is running.
Register address 0x1001
Designation
Watchdog function coding mask, function code 1...16, WDFCM_1_16
Access
Read / write
Default
0x0000
Description
Using this mask the function codes can be set to trigger the watchdog function.
The function code can be selected via a ‘1’ to
( = 2(Function code-1)+ ....)
Bit 1001.0 corresponds to function code1,
Bit 1001.1 corresponds to function code2...
The watchdog function is started if a value is not equal to zero. If codes from
non-supported functions are entered in the mask the watchdog will not start.
An existing fault is reset and writing into the process illustration is possible.
Also here changes cannot be made while the watchdog is running.
Register address 0x1002
Designation
Watchdog function coding mask, function code 17...32, WD_FCM_17_32
Access
Read / write
Default
0x0000
Description
Same function as above, however, with the function codes 17 to 32. These
codes are not supported, for this reason the default value of this register should
not be changed. It is not possible to modify this value while the watchdog is
running.
Register address 0x1003
Designation
Watchdog trigger, WD_TRIGGER
Access
Read / write
Default
0x0000
Description
This register is used for an alternative trigger method. The watchdog is trigge-
red by writing different values in this register. Values following each other
must differ in size. Writing of a value not equal to zero starts the watchdog. In
case of a watchdog fault this register is reset to zero.