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GFK-1527A Chapter 5 Fault Detection 5-7
5
The following actions are taken when a link has timed out.
1. Link Timeout fault is logged in the PLC Fault Table.
2. The OK and Local LEDs on the Redundancy Communications Module in the RCM to BTM
link that failed continue to be maintained (that is, they will stay ON and the Local LEDs reflect
the state of the Local unit) but the Remote LEDS are turned OFF. The LEDs on the other
RCM continue to be updated as long as that RCM is OK.
3. The module fault contact is set. If the failed link is through the Redundancy Communications
Module in the local main rack, then the SLOT_0X fault contact is set (X is the slot number for
the Redundancy Communications Module). If the failed link is through the Redundancy
Communications Module in the other unit's main rack, then the SLOT_71 fault contact is set.
4. The corresponding communications link is no longer used. If the other link is still operating,
then that link will be used for all further data transfer and units can remain in synchronization.
5. If no other communications link is available, then the unit functions as a stand-alone unit when
in RUN mode.
A power cycle or storing a hardware configuration to either unit is required to restore the link to
service. In this case, if the RCM is at fault, it will need to be replaced before power is restored.
Fault Actions in a CPU Redundancy System
Fault actions in the Hot Standby CPU Redundancy System are handled differently than fault
actions in a non-redundant system. Whenever there is a ready backup unit in the system, the fault
actions taken are not those normally specified in the configuration.
When the two CPUs are synchronized the following faults are considered FATAL and will cause
the affected unit to transition to STOP/FAULT mode.
any fault that degrades performance
any fault that causes loss of control of I/O
The configurable fault actions are applied whenever the system is running in stand-alone mode in
case you prefer fault tolerance (availability) versus safety (depending on the application).
Note
In a CPU redundancy system a
Fatal
fault from a Genius Bus Controller causes
the active unit to transition to
STOP/FAULT
mode. All
Diagnostic
faults allow
the CPU to continue to operate.