Description

Brief Product Description

The Allen-Bradley 1785-BCM is a specialized redundancy module for the PLC-5 platform that manages automated switchovers between primary and standby processors. It ensures continuous system operation by mirroring Data Highway Plus (DH+) and Remote I/O (RIO) traffic across a high-speed serial link.

Product Description

Redundant Processor Synchronization and Fault Recovery

The Allen-Bradley 1785-BCM serves as the architectural foundation for high-availability PLC-5 systems. This single-slot module facilitates a “hot backup” configuration by monitoring the status of a primary processor and maintaining a standby unit in a state of readiness. By utilizing a High-Speed Serial Link (HSSL), the 1785-BCM synchronizes critical data between the two controllers. If the primary unit encounters a hardware failure, power loss, or a software fault, the module executes an automated switchover. This transition ensures that the standby processor assumes control of the process with minimal disruption, effectively maximizing facility uptime and protecting sensitive industrial operations.

High-Speed Communication and Scannable Reliability

The module excels in managing high-bandwidth communication protocols, specifically supporting Data Highway Plus (DH+) and Remote I/O (RIO) networks. It handles data transfer rates up to 1.2 Megabaud, providing the speed necessary for real-time industrial synchronization. To manage high volumes of status information and network traffic during a switchover, the 1785-BCM features an internal 4K-word buffer. This buffer prevents data loss during the transition period. Furthermore, the module allows for manual switchovers when engineers shift the processor mode from Run to Program or Test, giving maintenance teams granular control over system redundancy during scheduled updates.

System Integration and Legacy Compatibility

Engineered for the 1771 I/O chassis, the 1785-BCM Allen-Bradley module integrates seamlessly with a wide range of legacy PLC-5 processors, including the PLC-5/15 (Series B), 5/20, 5/25, 5/30, 5/40, and 5/60. For a successful redundant setup, users must deploy the I/O modules in remote racks rather than the local processor chassis, ensuring that the distributed I/O stations remain accessible to both the primary and standby modules. Installation requires the use of a 1771-WG Wiring Arm to ensure secure and standardized termination of communication cables. Although this module entered legacy status in 2011, it remains a vital component for maintaining and repairing existing PLC-5 infrastructure.

Technical Specifications