Rockwell Automation 1785-BCM_BEM, D17856.5.4 PLC-5 Backup Communication Module User Manual - Manual (Page 68)

Operating Your PLC-5 Backup System
Chapter 5
5-4
This scheme, where status and block identification information are always
present, permits continuous verification of the data transfer, and if necessary,
the re-sending of a block of data if that block was not successfully transmitted.
In addition, the 1785-BCM modules exchange the status word over the HSSL
continuously (even when the processors are not in RUN mode). This constant
communication allows the modules to always have information about each
other.
Figure 5.2 shows transfer of data from the primary processor to the secondary
processor through the 1785-BCM modules. Note that the path of automatic
transfer of remote input data is represented by a dotted line.
Figure 5.2
Transferring Data With Block Transfer Instructions
in the PLC-5 Backup System
• • • • •
HSSL
REM I/O REM I/O
BTR BTW
Segment Segment
Block 1
(64 words)
Block 2
(64 words)
Block N
(64 words)
Block 1
(64 words)
Block 2
(64 words)
Block N
(64 words)
BTW
BTR
Block ID
Data
(62 Words)
Status
Block ID
Data
(62 Words)
Status
Block ID
Reserved
Primary PLC-5 Secondary PLC-5
Primary
1785-BCM
Secondary
1785-BCM
PRIMARY SYSTEM SECONDARY SYSTEM
#of Blocks in
Segment
#of Blocks in
Segment
Remote Inputs (discrete and analog values)
•
sent directly to the primary processor
•
transferred automatically to the secondary processor
Remote I/O Chassis
11054I