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4-18 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide
–
May 2000 GFK-1527A
4
Example 8: Invalid
The following situation is not valid. If detected, the units switch roles automatically and behave as
in Example 3 above.
Primary Unit Secondary Unit
Role
Backup Active
Operating Mode
RUN/ENABLED RUN/DISABLED
RUN Disabled Mode for GDB Control Strategy
The following guidelines apply to using RUN/DISABLED mode with the GDB Control Strategy.
1. If a unit is in RUN/DISABLED mode, its LOC_RDY %S reference and the remote unit's
REM_RDY %S reference are not set and the corresponding LEDs on the Redundancy
Communications Modules are OFF. This indicates that the unit (with LOC_RDY reference
off) is not available to drive outputs.
2. If a unit is in RUN/ENABLED mode and the other unit is in RUN/DISABLED mode, the unit
in RUN/ENABLED mode does not use its synchronized fault action table. Instead, it uses the
user-configurable fault actions since there is no backup available to drive outputs.
3. Since redundant outputs must always be transferred from the active unit to the backup unit
when using the GDB control strategy, if outputs are enabled on either unit, the outputs of the
active unit are driven by the Genius I/O blocks.
Note
If the backup unit is in RUN/DISABLED mode, the backup unit continues NOT
to drive outputs upon failure of the active unit and
therefore is not a true backup.