User Manual
Publication 1747-UM010B-EN-P - September 2003
1-24 Overview
Role of the 1747-BSN Module
As an integral part of the backup system, the 1747-BSN modules
enable high-speed communication between the two SLC processors
and permit the secondary processor to assume control of the process.
In addition, the 1747-BSN module provides:
• high-speed transfer of the data table values from the primary to
the secondary system (HSSL), to ensure that the secondary
system’s data table is a copy of the primary system’s (2K words
maximum per BSN module pair)
• exchange of information on the status of the primary and
secondary systems (LSL)
• automatic transfer to the secondary system of the remote input
• transfer of control from the primary processor to the secondary
processor when one of the following conditions occur:
– power failure or power loss
– major processor fault
– 1747-BSN module fault
• change in the primary processor’s mode from:
– RUN to PROGRAM (manual switchover)
– REM RUN to REM PROG
– REM RUN to REM TEST
• transfer of control from the primary processor to the secondary
when one of the following conditions is detected by the
secondary processor:
– communication timeout in the HSSL between the two
1747-BSN modules and primary system is not updating the
remote I/O
– transfer of control command from the primary 1747-BSN
• substitution of equipment without interruption of the process;
that is, the faulted system can be repaired while the other system
is controlling the process
• connections for remote I/O and Data Highway Plus network
(the 1747-BSN module routes the remote I/O network and the
Data Highway Plus network to the primary processor)
• isolation of the systems, in order to guarantee that a fault in one
system does not affect the other
• diagnostics information
• remote programming capability for secondary processor. The
secondary processor is in the DH+ network
• the capability of switching two communication channels (one
configurable as RIO or DH+ and one RS-232/485 for DH485)
• minimal user programming impact
• use of standard SLC 5/02 or later and 1746 platform