Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 77)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-30
Disable Outputs Command
The DISABLE OUTPUTS command lets you inhibit the backup processor
from taking control of outputs when the primary processor faults. This
command is useful during an on-line editing session in an application
where control of the outputs by the backup processor after switchover is
undesirable while the programs are different.
When the primary processor executes a message instruction containing the
DISABLE OUTPUTS command, the memory communication module
inhibits the backup processor from taking control of outputs when the
primary processor faults. Some conditions that influence the operation of
this command are:
If the primary processor is not in run mode, the memory communication
module disables the outputs of the backup processor regardless of your
selection for the outputs.
If the primary processor shuts down while the outputs are disabled, the
backup processor cannot take control of outputs.
If the primary processor encounters a memory DOWNLOAD command
while the DISABLE OUTPUTS command is executing, the memory
communication module temporarily enables the outputs of the backup
processor. At the conclusion of the memory download, the outputs will
be disabled.
To restore normal operation, you must re-enable the outputs by using the
ENABLE OUTPUTS command.
Enable Outputs Command
The ENABLE OUTPUTS command lets you re-enable the backup
processor to assume control of the outputs after switchover.
When the primary processor executes a message instruction containing the
ENABLE OUTPUTS command, the memory communication module
enables the outputs in the backup processor.