WAGO 750-830 Manual page 233

4.3.5.1 Description of the internal variables
4.3.5.1.1 Watchdog (Fieldbus failure)
The watchdog monitors the data transfer between the fieldbus master and the
controller. Every time the controller receives a specific request (as define in
the watchdog setup registers) from the master, the watchdog timer in the con-
troller resets.
In the case of fault free communication, the watchdog timer does not reach its
end value. After each successful data transfer, the timer is reset.
If the watchdog times out, a fieldbus failure has occurred. In this case, the
fieldbus controller answers all following MODBUS TCP/IP requests with the
exception code 0x0004 (Slave Device Failure).
In the controller special registers are use to setup the watchdog by the master
(Register addresses 0x1000 to 0x1008).
By default, the watchdog is not enabled when you turn the controller on. To
activate it, the first step is to set/verify the desired time-out value of the
Watchdog Time register (0x1000). Second, the function code mask must be
specified in the mask register (0x1001), which defines the function code(s)
that will reset the timer. Finally, the Watchdog-Trigger register (0x1003)
must be changed to a non-zero value to start the timer.
Reading the Minimum Trigger time (Register 0x1004) reveals whether a
watchdog fault occurred. If this time value is 0, a fieldbus failure is assumed.
The timer of watchdog can manually be reset, if it is not timed out, by writing
a value of 0x1 to the Restart Watchdog register (0x1007).
After the watchdog is started, it can be stopped by the user via the Watchdog
Stop register (0x1005) or the Simply Stop Watchdog register (0x1008)
4.3.5.1.2 Watchdog Register
The watchdog registers can be addressed in the same way as described with
the MODBUS read and write function codes. Specify the respective register
address in place of the reference number.
Register address 0x1000 (MODBUS Address 404097)
Designation Watchdog time, WS_TIME
Access
Default
Description
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
read / write
0x0000
This register stores the watchdog timeout value as an unsigned 16 bit value. The
default value is 0. Setting this value will not trigger the watchdog. However, a
non zero value must be stored in this register before the watchdog can be trig-
gered. The time value is stored in multiples of 100ms (e.g., 0x0009 is .9 seconds)
It is not possible to modify this value while the watchdog is running.
Fieldbus Communication
MODBUS Functions
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