Fault Behavior; Fieldbus Failure; Internal Bus Fault - WAGO 750 Series Manual

3.1.10 Fault behavior

3.1.10.1

Fieldbus failure

When a Modbus TCP fieldbus failure occurs (e.g., the Ethernet cable is
removed or broke), the outputs that are controlled by the fieldbus port remain
in their current state by default. If this behavior is undesirable, a fieldbus
watchdog timer can be programmed to monitor Fieldbus communications.
The watchdog monitors the data transfer between the master controls and the
PFC. In the event of a watchdog timeout (i.e., there is a Fieldbus failure), the
PFC can be programmed to control the state of the outputs, based on your
application needs. In the case of fault free communications, the watchdog
timer will not timeout, since after each successful data transfer the watchdog
timer is reset.
Monitoring the watchdog time in the PFC is done by using the function block
'FBUS_ERROR_INFORMATION' in the control program. This function is
part of the "mod_com.lib" library.
Fig. 3-17: Function block for determining a fieldbus failure
'FBUS_ERROR' (BOOL) = FALSE = no fault
'ERROR' (WORD)
More information
For detailed information to the Watchdog register see the Chapters "MODBUS
Functions"; "Watchdog (Fieldbus failure)" and "Watchdog Register".
3.1.10.2

Internal bus fault

When an internal bus fault occurs (e.g., an I/O module is removed), all output
modules turn off. Additionally, the "I/O" LED blinks red and generates a fault
message. This message is decoded from the blink code, in the form of a fault
code and fault argument.
Once the internal bus fault is fixed, the controller is restarted by cycling its
power. At this point the transfer of the process data resumes and the outputs
are updated.
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
Fieldbus Controller 750-841
= TRUE = fieldbus failure
= 0 = no fault
= 1 = fieldbus failure
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Fault behavior
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