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

Configured for dual-channel ControlNet redundant network execution in ControlLogix backplane architectures, the Allen-Bradley 1756-CN2R/D (1756-CN2R/D ControlNet redundant communication module) provides direct physical and protocol-level routing of deterministic network frames across A/B media paths within industrial automation controller systems. The module maintains synchronized multi-path data transmission for up to 100 simultaneous ControlNet connections through backplane-managed scheduling.

Manufactured within the Rockwell Automation ControlLogix platform family, the unit integrates EtherNet/IP deterministic networks and ControlNet scheduling logic at the backplane interface layer to maintain continuous communication flow during redundancy operation.

Suffix Breakdown & Model Matrix

Single catalog configuration. No functional sub-variants defined beyond 1756-CN2R/D revision level within ControlLogix ControlNet redundant communication module series.

Hardware Specifications

ControlLogix Backplane Deterministic Network Execution

The 1756-CN2R/D executes ControlNet scheduling through ControlLogix backplane arbitration, where cyclic data packets are aligned with deterministic scan intervals. Redundant A/B channel operation is maintained at the media interface layer, allowing continuous propagation of network frames without application-layer intervention.

EtherNet/IP deterministic networks are coordinated through backplane bus communication scheduling, ensuring predictable data delivery timing between controller tasks and distributed I/O nodes. The redundancy logic operates independently of controller program execution, maintaining continuous synchronization across both ControlNet paths.

Frequently Asked Questions (FAQ)

Q: Does the 1756-CN2R/D support hot-swap operation in ControlLogix chassis?
A: Yes. The module supports hot insertion and removal, provided the chassis backplane reinitialization sequence is completed and configuration is retained in controller memory.

Q: How is redundancy handled between ControlNet A and B channels?
A: Both channels operate in parallel with synchronized transmission. Redundancy is maintained at the network interface layer, with no galvanic isolation between A and B paths.

Q: What limits the number of simultaneous ControlNet connections?
A: The module supports up to 100 connections, constrained by backplane bandwidth allocation and ControlNet scheduling capacity.

Field Installation Guidelines

Install the module into a compatible ControlLogix chassis slot ensuring full backplane connector engagement to maintain deterministic communication timing. ControlNet cabling must follow impedance-matched routing with continuous shielding integrity across trunk and drop segments.

Maintain physical separation between ControlNet media and high-frequency power conductors to reduce electromagnetic coupling. Shield termination should be implemented at a single-point earth reference to avoid ground loop formation across redundant A/B channels.

Verify firmware compatibility between controller, chassis, and communication module prior to commissioning to ensure consistent backplane synchronization and network scheduling alignment.