GFK-1527A Chapter 4 Normal Operation 4-15
4
RUN Disabled Mode
RUN/DISABLED mode causes all physical outputs to go to their default state in that PLC. Inputs
are still scanned and logic i s solved. A CPU in RUN/DISABLED mode may be the active unit.

RUN Disabled Mode for GHS Control Strategy

There are several guidelin es for using RUN/DISABLED mode when using th e G HS Con trol
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 an d the corresponding LEDs on the Redun dan cy
Communications Modules are OFF. This indicates that the unit (with LOC_RDY reference
off) is not available to drive outputs.
2. You cannot command a role switch from an active unit that is in RUN/ENABLED mode to a
unit that is in RUN/DISABLED mode. The Redundancy Communication Module role switch
pushbutton and SVCREQ #26 are ignored if a role switch is attempted in this situation.
3. If the units are transitioned so that the Primary Unit is active with outputs disabled and the
Secondary Unit is the backup with outputs enabled, the Primary Unit continues to solve logic
and transfer outputs to the backup, and the backup unit drives the transferred outputs.
4. If units are transitioned in any manner where the Secondary Unit is active with outputs
disabled and the Primary Unit is the backup with outputs enabled, the units automatically
switch roles, so that Primary Unit becomes active in RUN/ENABLED mode.
5. If a unit is in RUN/ENABLED m od e an d the other unit is in RUN/DISABLED, the unit in
RUN/ENABLED 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.
Note
If the backup unit is in RUN/DISABLED mode, the backup unit continues to
NOT drive output s upon failure of th e active unit and therefore is not a true
backup.

Example 1: Role switches allowed on both unit s

Primary Unit Secondary Unit
Role Active Backup
Operating Mode RUN/ENABLED RUN/ENABLED
OK LED on RCM ON ON
LOC_RDY LED on RCM and %S Bit ON ON
LOC_ACT LED on RCM and %S Bit ON OFF
REM_RDY LED on RCM and %S Bit ON ON
REM_ACT LED on RCM and %S Bit OFF ON