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1-8 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide
–
May 2000 GFK-1527A
1
Control Strategies
There are two different Control Strategies for Enhanced Hot Standby CPU Redundancy: GHS
and
GDB.
GHS Control Strategy
The GHS control strategy has the following features:
Multiple single bus Genius I/O networks with redundant controller in each synchronized PLC
Multiple local single bus Genius I/O networks
Redundant Genius I/O driven exclusively by the active unit
Primary Unit is always the Active Unit in synchronized system unless explicitly overridden by
user or application; switchover from secondary active to primary active may not be bumpless
in certain failure conditions
Only critical control data must be transferred from Active to Backup CPU
Compatible with the release 4 based Hot Standby Redundancy Product (CPU780)
GDB Control Strategy
The GDB control strategy has the following features:
Multiple dual bus Genius I/O Networks with redundant controllers in each synchronized PLC
Multiple single bus Genius I/O networks with redundant controller in each synchronized PLC
Multiple local Genius I/O networks with single or dual buses or controllers
Active unit does not automatically switch to Primary on resynchronization
Bumpless switchover with either PLC active
Critical control data plus all redundant outputs must be transferred from Active to Backup
CPU