Technical data
BACnet/IP Controller 750-830 • 135
Fault behavior
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
3.1.10 Fault behavior
3.1.10.1 Loss of Fieldbus - MODBUS
A fieldbus and, hence, a link failure is recognized when the set reaction time
for the watchdog expires without initiation by the higher-order control system.
This may occur, for example, when the Master is switched off, or when there
is a disruption in the bus cable. An error at the Master can also result in a
fieldbus failure. No connection via ETHERNET.
The MODBUS watchdog monitors the ongoing MODBUS communication via
MODBUS protocol. A fieldbus failure is signaled by the red "I/O" LED light-
ing up, provided the MODBUS watchdog has been configured and activated
(see section 4.3.5.1.1), Fieldbus monitoring independently of a certain proto-
col is possible using the function block 'FBUS_ERROR_INFORMATION' in
the library 'Mod_com.lib'. This checks the physical connection between mod-
ules and the controller and assumes evaluation of the watchdog register in the
control system program. The I/O bus remains operational and the process im-
ages are retained. The control system program can also be processed inde-
pendently.
Fig. 3-24: Function block for determining loss of fieldbus, independently of protocol g012926x
'FBUS_ERROR' (BOOL) = FALSE = no fault
= TRUE = Loss of field bus
'ERROR' (WORD) = 0 = no fault
= 1 = Loss of field bus
The node can be put into a safe status in the event of a fieldbus failure with the
aid of these function block outputs and an appropriately programmed control
system program.
Additional Information
Loss of fieldbus detection through MODBUS protocol:
For detailed information about the watchdog register, refer to section
4.3,
"MODBUS Functions", in particular 4.3.5.1.1, "Watchdog (Response on loss
of fieldbus)".
Protocol-dependent loss of fieldbus detection:
You can obtain the library 'Mod_com.lib' with the function block
'FBUS_ERROR_INFORMATION' free of cost at the website
http://www.wago.com under Downloads ! AUTOMATION ! WAGO-I/O-
PRO Libraries ! Mod_com.lib