Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 124)

Publication 1785-UM024B-EN-P - January 2003
F-2 Comparison to the 1785-BCM System
In terms of how data is provided to the two PLC-5 systems, similar to
the BCM system, the ControlNet PLC-5 backup system does
automatically present the ControlNet input data (both discrete and
analog) to both PLC-5 processors. Unlike the BCM, however, the
ControlNet PLC-5 backup system does NOT provide the remote
output data (discrete and analog) to both PLC-5s. The secondary
PLC-5 in the ControlNet PLC-5 backup system generates its own
output data based upon internal program execution. Should you wish
to do so, you can develop and implement message instructions to
crossload output data from one PLC-5 processor to the other.
Another difference in the two backup systems is that the ControlNet
backup system does NOT provide a Customer Relay.
Because of the system architecture, it is possible with the ControlNet
backup system to have MMI devices actively communicating with
both the Primary and Secondary PLC-5s.