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.

4-18

Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide – May 2000

GFK-1527A

Page 57
Image 57
GE 90-70 manual Example 8 Invalid, RUN Disabled Mode for GDB Control Strategy