Rockwell Automation 1785-BCM_BEM, D17856.5.4 PLC-5 Backup Communication Module User Manual - Manual (Page 148)

Appendix
B
B-1
Reference Information
This appendix provides the following reference information:.
answers to PLC-5 backup configuration questions
formulas for determining delay and transfer times between the primary
and secondary processors
The following questions may arise when you are configuring a PLC-5
backup system. We’ve provided answers to these questions and also
provided references to pages in this manual and to other publications to
help you find more information if needed.
Q. What size I/O chassis should I use for installing the PLC-5
processors in the backup system?
A. You can use any size chassis for the PLC-5 processors. However,
keep in mind that only the PLC-5 processor, power supply, the
1785-BCM module, and the 1785-BEM module (if any) will reside in
the chassis; therefore, we recommend a 4-slot chassis (cat. no.
1771-A1B).
Q. Can I install I/O modules in the local I/O chassis?
A. The PLC-5 backup system does not back up local I/O. Since the
objective of having a backup system is to guard against interruptions
due to shutdown of your operation, we recommend that you do not
install modules for controlling your process in the local chassis. (Refer
to page 3-1 for more information.)
Q. In which slot of the local I/O chassis do I install the 1785-BCM
module?
A. You can install the 1785-BCM module in any slot of the I/O chassis.
We, however, recommend that you install the module in the left-most
slot of the first I/O module group in the I/O chassis for ease in making
connections and programming. (Refer to Chapter 3 for more
information.)
Appendix Objectives
Answers to PLC-5 Backup
Configuration Questions