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Fieldbus controller 750-842
Fault behavior
Modular I/O System
ETHERNET TCP/IP
3.2.9 Fault
behavior
3.2.9.1 Fieldbus
failure
A fieldbus failure is given i. e. when the master cuts-out or the bus cable is in-
terrupted. A fault in the master can also lead to a fieldbus failure.
A fieldbus failure is indicated by illuminating the red "ERROR"-LED.
If the watchdog is activated, the watchdog-register is evaluated in the case of
fault free communication.
The evaluation of the watchdog register is made using the function block
’FBUS_ERROR_INFORMATION’ in the control program. The internal bus
remains in function and the process illustrations are retained. The control pro-
gram can be further processed independently.
Fig. 3-37: Function block for determining a fieldbus failure
g012926x
’FBUS_ERROR’ (BOOL) = FALSE = no fault
= TRUE = fieldbus failure
’ERROR’ (WORD)
= 0 = no fault
= 1 = fieldbus failure
The nodes can set to a safe status in the case of a fieldbus failure using these
outputs and a corresponding control program.
i
More information
For detailed information to the Watchdog register see Chaper 6.2.12
"Watchdog (Fieldbus failure)".
3.2.9.2
Internal bus fault
An internal bus fault is created, for example, if an I/O module is removed. If
this fault occurs during operation, the output modules behave in the same
manner as an I/O module stop.
The "I/O" LED blinks red.
The controller generates a fault message (fault code and fault argument).
Once the internal bus fault is fixed, the controller starts up following power
being cycled as during a normal start-up. The transfer of the process data is
then resumed and the node outputs are correspondingly set.
