Allen-Bradley 1747-DCM Data Highway Plus Communications Module

The Allen-Bradley 1747-DCM Direct Communication Module is a DH+ (Data Highway Plus) interface that enables data exchange between a supervisory AB controller and distributed SLC-500 controllers over the Data Highway Plus network via the RIO Link. This 1/4‑rack module installs in an SLC 500 modular chassis and does not scan its own local I/O; instead, it passes supervisory data between controllers, forming a distributed processing system. It supports Data Highway Plus speeds of 57.6, 115.2, or 230.4 kb/s and provides dual DH+ data lines with a shield connection for robust, noise‑tolerant communication. By bridging DH+ networks to non‑DH+ AB controllers, the 1747-DCM enables data exchange and coordination across multiple controllers, facilitating remote I/O and cross‑rack communication on existing DH+ installations. Typical applications include linking an SLC‑500 system to a PLC‑5 or to other SLC processors over DH+ to share discrete data, control status, and messages without duplicating I/O in each rack.