Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 56)

Publication 1785-UM024B-EN-P - January 2003
4-2 Using I/O in Your ControlNet Hot Backup System
This non-redundant I/O should only be used when all the
consequences of its operation are fully understood.
Redundant Connections
Redundant connections are required so that the PLC-5 ControlNet Hot
Backup system can properly switch over ownership of the scheduled
output from the former primary PLC-5 to the current primary PLC-5.
You must configure identical redundant connections for both PLC-5
programmable controllers to an I/O rack for discrete I/O or to specific
I/O modules.
Once both PLC-5 programmable controllers establish the redundant
connection, the scheduled output will only be used from the primary
PLC-5. The outputs from the secondary PLC-5 are discarded. However,
even after the outputs from the secondary PLC-5 are discarded, the
connection from the secondary PLC-5 remains open. This allows the
secondary PLC-5 to quickly take control of the outputs in the event of
a switchover.
The scheduled inputs for a redundant connection are sent to both
PLC-5 programmable controllers simultaneously, insuring that both the
primary and secondary PLC-5 programmable controllers receive the
scheduled inputs at the same time.
If only one of the redundant connections is established, it works
exactly like an exclusive owner connection. It is only when both of
the redundant connections are established to an I/O chassis or
module that special handling of the scheduled outputs occurs.
There are three adapter modules that support redundant connection
in the ControlNet Hot Backup system:
• 1771-ACN(R) adapter - with this adapter, the rack connection
must be established before any module connections can be
established
• 1794-ACN(R) FLEX I/O adapter
• 1747-ACN(R) SLC I/O adapter
How to Configure Redundant Connections
Configuration parameters of a redundant connection must be the
same for both the primary and secondary PLC-5. If any of the
configuration parameters are different, the second of the two
connections that attempts to be established will fail with a Redundant
Connection Mismatch error.