Product Overview

The Allen-Bradley 1785-BCM is a specialized redundancy interface designed for the PLC-5 platform to ensure continuous system operation and communication uptime. This module facilitates a "hot backup" configuration by managing the synchronization and switchover between a primary and a secondary (standby) PLC-5 processor. By monitoring the health of the active controller, the 1785-BCM can trigger an instantaneous transfer of control to the standby unit in the event of hardware failure, power loss, or software faults.

Occupying a single slot in a 1771 I/O chassis, the 1785-BCM is engineered for mission-critical applications where downtime is not an option. It provides the high-speed logic necessary to maintain the integrity of Data Highway Plus (DH+) and Remote I/O (RIO) networks during transition, ensuring that field devices and supervisory systems remain connected.

Key Technical Characteristics

The 1785-BCM utilizes a dedicated High-Speed Serial Link (HSSL) to coordinate data between the twin processor sets, offering robust performance for legacy industrial networks.

• Network Support: Fully compatible with Data Highway Plus (DH+) and Universal Remote I/O (RIO) protocols.

• Switchover Velocity: Supports high-speed data transfer rates up to 1.2 Megabaud via the HSSL connection.

• Data Buffering: Equipped with a 4K-word internal memory buffer to prevent data loss during processor status updates.

• Trigger Mechanisms: Automatic switchover occurs upon detection of processor parity errors, watchdog timeouts, power failures, or manual mode changes (e.g., Run to Program).

• Hardware Interface: Requires the 1771-WG wiring arm for secure field-side communication terminations.

Compatibility and Installation

This module is designed to integrate specifically with the Classic and Enhanced PLC-5 processor families within a 1771 chassis environment.

• Processor Support: Compatible with PLC-5/15 (Series B or later), PLC-5/20, PLC-5/25, PLC-5/30, PLC-5/40, and PLC-5/60.

• Chassis Requirement: Must be installed in a 1771 I/O chassis. Note that in backup configurations, I/O is typically handled through remote racks to allow both processors access to the same field data.

• Expansion Capabilities: Can be paired with the 1785-BEM (Backup Expansion Module) for systems requiring additional communication channel redundancy.

Physical Specifications

• Weight: 0.56 kg (1.23 lbs)

• Dimensions: 3.0 x 14.7 x 25.8 cm

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Storage Temperature: -40°C to 85°C (-40°F to 185°F)

• Relative Humidity: 5% to 95% (non-condensing)