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82 Series 90-70 Hot Standby CPU Redundancy User’s Guide – December 1993
GFK-0827
If an RCM fault is detected, proceed as follows:
STOP the unit with the suspected bad RCM.
Turn power off at that rack.
Unplug the terminated cable from the RCM and replace the module.
Reconnect the terminated cable.
Power-up the rack (mode switch is still in STOP).
Verify that the REMOTE ACTIVE and REMOTE READY LEDs are on, or look at the
%S bits in the stopped unit. Note that the RCM LEDs only update if the board is not
faulted.
Switch the repaired unit to RUN.
Redundancy Communications Link Failures
There are two types of Redundancy Communications Link failures; a ”Link Timeout”
and a ”Hard Link Failure”. When a Link Timeout occurs, the RCM BOARD OK LED will
remain ON and the LOCAL READY and LOCAL ACTIVE LEDs will continue to reflect
the status of the Local unit. The REMOTE ACTIVE and REMOTE READY LEDs will not
be updated by the Remote unit until the link is reinitialized by storing a configuration or
power cycling either unit. When a Hard Link Failure occurs, all five RCM LEDs will be
OFF. A power cycle of the Local unit is required to attempt to reinitialize the failed link.
Bus Transmitter Module
A fault in the BTM is treated just like a fault in the RCM. It is only fatal if the fault
prevents communications to any expansion racks within the system.
Failure of the BTM module may not easily be distinguished from an RCM cable failure or
even an RCM failure. However, most failure modes of the BTM can be isolated to the
BTM. When a BTM fails, the system will respond as described for the RCM and cable
failure, it will only fault the active PLC if the active PLC has expansion racks with critical
components installed.
The BTM can be replaced by removing power from the rack and replacing the BTM.
When power is restored to the CPU, the CPU will obtain synchronization with the active
system and either take control or become the backup CPU.
Genius Bus Controller
In a synchronized Hot Standby CPU Redundancy system, all GBC faults are considered
fatal. The failure of a Genius bus controller will be detected and isolated by the PLC. If a
GBC fails in the active PLC, the active PLC will fail and the backup will assume control.
The GBC can be replaced by removing power from the rack and replacing the GBC.
When power is restored to the CPU, the CPU will obtain synchronization with the active
system and either take control or become the backup CPU.