Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 54)

Publication 1747-UM010B-EN-P - September 2003
4-2 Operating Your SLC 500 Backup System
The secondary 1747-BSN module responds with current data to the
remote I/O scan requests of the secondary processor, making the
secondary processor “think” that it is communicating with remote I/O
chassis. This response prevents remote I/O faults in the secondary
processor, since the secondary BSN module is not physically
connected to the remote I/O link.
In addition to providing the secondary processor a copy of the remote
discrete input image table, the 1747-BSN modules in both systems
work together to provide the secondary processor a copy of block
transfer data read from the remote I/O chassis.
The 1747-BSN automatically exchanges system status information
when communicating with another 1747-BSN through the High-
Speed Serial Link (HSSL). Both modules are continuously
communicating with each other, even when both processors are not
in Run mode. This is achieved by sending and receiving the system
status words. This information can be read from either module at any
time and provides for both SLC 5/0x (primary and secondary) the
“other side status”. HSSL is also used to transfer user data table data,
up to 2K total per BSN module.
RS-232/485 Communication Channel
The RS-232/485 channel is a dumb communication channel which is
used to switch the connection to one operator interface or other serial
communications device (through RS-232/485). The communication
channel relays are closed when the module is primary; otherwise the
relays are open as shown in the figure below.
Primary Secondary
SLC 5/03 1747-BSN
To Operator Interface
1747-BSN SLC 5/03