Allen-Bradley 1756-CN2R/C ControlLogix ControlNet Redundant Communication Module

The Allen-Bradley 1756-CN2R/C, also cataloged as the 1756-CN2R/C ControlLogix ControlNet redundant communication module, operates as a dedicated hardware interface for deterministic ControlNet data exchange and redundant A/B channel network routing within ControlLogix backplane architectures. Configured for dual-channel ControlNet communication in ControlLogix systems, the 1756-CN2R/C provides direct physical transmission handling for up to 100 simultaneous network connections across redundant paths.

Manufactured under Rockwell Automation ControlLogix platform architecture, the module executes backplane-to-network protocol handling via ControlNet media, maintaining synchronized communication frames across redundant channels without galvanic separation between A and B paths.

Suffix Breakdown & Model Matrix

Single configuration model. No documented functional suffix segmentation beyond catalog designation 1756-CN2R/C within ControlLogix ControlNet redundant communication module family.

Hardware Specifications

ControlNet Redundant Backplane Communication Architecture

The 1756-CN2R/C integrates into the ControlLogix backplane, where cyclic data is scheduled via deterministic ControlNet media access control. The module maintains dual-channel synchronization across A and B ControlNet segments, ensuring continuous frame-level alignment for redundancy switching without requiring external arbitration logic. Backplane-to-network throughput is managed through the ControlLogix internal communication scheduler, supporting multi-node distributed I/O and controller interlocking structures.

Redundancy handling is implemented at the network interface layer; both channels remain active, with real-time propagation of scheduled data packets across parallel media paths. Channel switching behavior is constrained by ControlNet scheduling integrity rather than application-layer intervention.

Frequently Asked Questions (FAQ)

Q: Does the 1756-CN2R/C support hot-swap in ControlLogix chassis?
A: Yes. The module supports removal and insertion under chassis power, provided ControlLogix system configuration allows module re-registration through Studio 5000 and network resynchronization is complete.

Q: Is there galvanic isolation between ControlNet A and B channels?
A: No. The A and B channels share basic insulation only; there is no galvanic isolation between redundant media paths.

Q: What limits apply to simultaneous ControlNet connections?
A: The module supports up to 100 simultaneous ControlNet connections, constrained by network scheduling bandwidth and ControlLogix backplane communication capacity.

Field Installation Guidelines

Ensure the module is inserted into a compatible ControlLogix chassis slot with proper backplane seating to maintain signal integrity across the communication interface. ControlNet coaxial cabling must follow standard impedance-matched routing practices, with consistent shielding continuity across trunk and drop segments.

Maintain separation between ControlNet media and high-noise power conductors to reduce induced coupling. Shield grounding should be terminated at a single-point earth reference to prevent ground loop formation across redundant channels. Avoid sharp bending radii in coaxial runs to preserve impedance stability.

Chassis firmware and module revision compatibility must be verified prior to commissioning to ensure backplane scheduling consistency and network synchronization stability.