Rockwell Automation 1785-BCM_BEM, D17856.5.4 PLC-5 Backup Communication Module User Manual - Manual (Page 20)

Understanding the 1785-BCM
Hardware Components
Chapter 2
2-4
Table 2.A
Communication Ports
Communication Port: This link is used to:
High Speed Serial Link (HSSL) permit two-way alternating communication (half-duplex)
between the two 1785-BCM modules of the backup system
at a distance of up to 15 feet.
Channel 1A connect the primary PLC-5 processor to the Data Highway
Plus network or to the remote I/O link; the secondary
processor is isolated from this link.
Channel 1B connect the primary PLC-5 processor to the Data Highway
Plus network or to the remote I/O link; the secondary
processor is isolated from this link.
Channels 1A and 1B have a default communication mode which can be
changed by resetting switches, if necessary. Table 2.B describes the default
communication mode for each of the two channels.
Table 2.B
Default Communication Modes
Channel Default Communication Mode
1A Data Highway Plus
1B Remote I/O – Scanner mode at 57.6 kbaud
With the exception of the HSSL, all of the connections in the 1785-BCM
module have an internal relay whose contacts are closed when the
controller is primary and open when the processor is secondary. Figure 2.3
shows these relays for processor A and processor B of a PLC-5 backup
system.