Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 14)

Choosing a Backup Configuration
Chapter 1
1-7
The three methods of switching control of outputs from the primary to the
backup processor are:
automatic switchover with no switchback
automatic switchover with controllable switchback
manual
switchover
You can use any one of these methods for scanner backup, but you must
use automatic switchover with controllable switchback for MX backup.
Table 1.C lists the attributes associated with each method.
Table 1.C
Switchover Method Attributes
Switchover
Method:
Attributes:
Automatic
Switchover with
No Switchback
Ć Backup processor automatically takes control of outputs when the primary
processor faults.
Ć No operator intervention required at switchover.
Ć Shutting off the primary processor initiates switchover.
Ć Both the primary and the backup processor must be shut down and
restarted when reĆinstalling a repaired processor.
Ć Not recommended for applications using multidrop modems with 1775ĆKA
modules because the modem port is not disabled after a processor fault.
Automatic
Switchover with
Controllable
Switchback
Ć Backup processor automatically takes control of outputs when the primary
processor faults.
Ć No operator intervention required at switchover.
Ć Shutting off the primary processor initiates switchover.
Ć Either processor can be the primary" processor.
Ć The backup processor does not have to be shut down when reĆinstalling a
repaired primary processor.
Ć Not recommended for applications using multidrop modems with 1775ĆKA
modules because the modem port is not disabled after a processor fault.
Continued on Next Page
Choosing a Switchover
Method