Filter
Top Products
4
65GFK-0827 Chapter 4 Operation
Differences in Operation for CPU 780
The following features operate differently with the CPU 780 than they do with other
Series 90-70 CPUs:
RUN/DISABLED mode
Configuration of Fault Actions
STOP to RUN mode transition
Background Window Time (default is different)
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 is solved. A CPU in RUN/DISABLED mode may
be the active unit.
There are several guidelines that you should be aware of regarding the use of the
RUN/DISABLED mode.
1. If a unit is in RUN/DISABLED mode, its LOC_RDY %S reference and the remote
unit’s REM_RDY %S reference will not be set and the corresponding LEDs on the
RCMs will not be ON. 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 RCM role switch pushbuttons
and SVCREQ #26 will be ignored if a role switch is attempted in this situation.
3. If the units are transitioned when the primary unit is active with outputs disabled
and the secondary unit is backup with outputs enabled, the primary unit will
continue to solve logic and transfer outputs to the backup, and the backup unit will
drive 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 backup with outputs enabled, then the
units will automatically role switch so that the primary unit becomes active in
RUN/ENABLED mode.
5. If a unit is in RUN/ENABLED and the other unit is in RUN/DISABLED, the unit in
RUN/ENABLED will not use its synchronized fault action table. Instead, it will use
the user-configurable fault actions since there is no backup available to drive
outputs.
Note
If the backup unit is in RUN/DISABLED mode, then the backup unit will
continue to NOT drive outputs upon failure of the active unit and
therefore is not a true backup.