Fault Behavior; Loss Of Fieldbus; Figure 80: Function Block For Determining Loss Of Fieldbus, Independently Of Protocol - WAGO -I/O-SYSTEM 750 Manual

206 Diagnostics
11.2

Fault Behavior

11.2.1

Loss of Fieldbus

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 lighting up,
provided the MODBUS watchdog has been configured and activated.
Fieldbus monitoring independently of a certain protocol is possible using the
function block 'FBUS_ERROR_INFORMATION' in the library "Mod_com.lib". This
checks the physical connection between modules and the controller and
assumes evaluation of the watchdog register in the control system program. The
I/O bus remains operational and the process images are retained. The control
system program can also be processed independently.

Figure 80: Function Block for Determining Loss of Fieldbus, Independently of Protocol

'FBUS_ERROR' (BOOL)
'ERROR' (WORD)
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.
Manual
1.5.0
750-882 Media Redundancy ETHERNET Controller
FBUS_ERROR_INFORMATION
FBUS_ERROR
ERROR
= FALSE
= TRUE
= 0
= 1
WAGO-I/O-SYSTEM 750
= no fault
= loss of field bus
= no fault
= loss of field bus