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5-14 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide
–
May 2000 GFK-1527A
5
Dual Bus Networks
For dual bus Genius networks, a single trunk cable failure will result in the blocks downstream
from the failure switching to the other Genius bus. Since both busses are attached to the same
Genius blocks no loss of inputs or outputs will result.
Failures in bus stubs (the portion from a BSM to its associated blocks) result in the loss of the
blocks on that bus stub that are downstream from the failure. These blocks will be lost for both the
active and the backup unit.
The failed Genius bus can be repaired without disturbing power to either system and thus without
disturbing which PLC is in control of the process. To repair a failed trunk cable, first disconnect
the failed bus from both GBCs which will cause any remaining blocks on that bus to switch to the
other bus; the failed bus can then be replaced. Failure of a Genius bus stub can be done online but
will result in the loss of any remaining blocks on that stub until the bus is repaired.
Genius Blocks
The failure of a single block is not fatal when the PLCs are synchronized.
If the fault action of LOSS OF OR MISSING I/O MODULE is configured to be Fatal, the failure
of a single block will be fatal when the PLCs are not synchronized.