Allen-Bradley 1785-BCM Backup Communication Module

Description

The Allen-Bradley 1785-BCM Backup Communication Module is a high-speed, legacy backup communication module designed exclusively for the PLC-5 programmable logic controller system, though it is now obsolete and no longer fully supported. As a single-slot chassis module, its core function is to provide communication redundancy and automatic switchover between a PLC-5 main processor and a standby processor, ensuring uninterrupted operation during critical events. It supports high-speed backup for Data Highway Plus (DH+) and Remote I/O (RIO) links via a high-speed serial link, with a maximum switchover speed of 1.2 megabaud. Equipped with an internal buffer of up to 4K words, the module can initiate switchover in response to multiple trigger events, including power failures, processor errors, partner 1785-BCM module faults, and manual mode transitions such as from RUN to PROGRAM, REMOTE RUN to REMOTE PROGRAM, or changes between REM RUN and REMOTE TEST modes. It is compatible with PLC-5/20, 5/30, 5/40, and 5/60 processors, requiring a series B revision C or higher for proper operation, and has a weight of 4 lbs.