Allen-Bradley 1785-BEM Backup Communication Module

Essential Technical Specifications

• Manufacturer: Allen-Bradley / Rockwell Automation
• Model Number: 1785-BEM
• System Series: PLC-5
• Module Function: Backup Communication Expansion
• Backplane Current Draw: 0.6 Amps @ 5V DC
• Data Transfer Speed: Up to 1.2 Mega Baud
• Interface Ports: DH+ and Remote I/O (RIO) via 1771-CD
• Auxiliary Output: Factory-installed 0.25A relay @ 24V DC
• Wiring Compatibility: 26-14 AWG Field Wiring Arm
• Operating Temperature: 0°C to 60°C (32°F to 140°F)
• Storage Temperature: -40°C to 85°C (-40°F to 185°F)
• Certifications: CE, UL, and CSA
• Weight: 0.52 kg

Configuration and Network Integration

The front-facing switch assembly allows for rapid hardware configuration through four adjustable switches. These manual controls define the specific operational modes for the backup communication link. Additionally, the module uses the specialized 1771-CD cable connector to maintain high-integrity signal paths. This ensures that DH+ and Remote I/O protocols operate at peak performance without interference.

Installation remains simple due to the standardized 1771 chassis design and mechanical keying. The module uses specific backplane pin connections to verify correct placement during system setup. Furthermore, the integrated field wiring arm supports a wide range of cable gauges for secure terminations. These mechanical features contribute to a stable and vibration-resistant communication interface.

Diagnostic Monitoring and Field Reliability

The 1785-BEM provides clear operational feedback through its front-panel status indicators. These LEDs inform technicians about processor states, active forces, and communication health. Consequently, troubleshooting becomes faster and more accurate during routine system maintenance. The module also features a small relay for external fault signaling or interlock logic.

This hardware withstands demanding industrial environments while maintaining strict safety compliance. It operates effectively in high-humidity conditions without sacrificing data throughput. Although Rockwell officially retired this model in 2011, our brand-new units support vital legacy upgrades. This module provides a proven solution for extending the life of existing PLC-5 architectures.