Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 55)

I/O Communication
Chapter 3
3-7
Important: Remember to reset the counter for the MVF, or the move
operation does not function properly.
Backup Communication
You can use the backup communication with the PLC-3 or PLC-3/10
backup feature. The backup feature has an I/O listening mode that enables
the backup system to monitor input data. To transfer other information to
the backup system, you can install a backup communication channel
(Figure 3.5).
With a backup communication channel, you can program data transfers
between the primary and backup controller (Figure 3.5). Then, when the
primary controller shuts down, the backup controller has up-to-date data
for running your application. Such data could be storage, block transfer,
timer, or counter information.
Figure 3.5
Using a Backup Communication Channel
Twinaxial cable for setting
up backup communication
channel.
15412
Primary System Backup System
Backup cable for
setting up type of
switchover.
Important: You cannot use peer-to-peer communication to
communication between the primary and backup system because the
backup processor listens but does not respond to communication received
on a peer-to-peer communication channel.
You configure the primary and backup controllers for the backup
communication channel through LIST. Communication occurs via files
that you specify in LIST (Figure 3.6).