Allen-Bradley 1785-BCM Backup Communication Module

The Allen-Bradley 1785-BCM Backup Communications Module is a PLC-5 backup communications device that provides rapid switchover for Data Highway Plus (DH+) and Remote I/O (RIO) paths to keep critical control data flowing when the primary network path fails. It implements two DH+/RIO interfaces and a single high-speed serial link interface, enabling redundant communications between the PLC-5 processor, DH+/RIO networks, and I/O devices. The module mounts in the PLC-5 system backplane and requires no external power; it supports up to four BCM modules per system. Physical specifications include dimensions of 4.5 by 12.4 by 6.3 inches (115 x 317 x 160 mm) and a weight of about 0.3 lb (0.1 kg). It features conformal coating for environmental protection and per-channel diagnosis/status LEDs to indicate link health and fault conditions. A wiring arm is available (1771-WN) for secure mounting within the rack. Compatible with PLC-5 processors and the DH+/RIO network architecture of the era, the 1785-BCM is part of the PLC-5 backup communications family and provides the redundancy needed for critical control loops.