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

Configured for deterministic ControlNet packet exchange within ControlLogix backplane architectures, the Allen-Bradley 1756-CN2R/B (1756-CN2R/B communication module) provides direct physical and protocol-level execution of redundant A/B channel data transfer across ControlNet network segments under the ControlLogix distributed I/O communication framework.

Suffix Breakdown & Model Matrix

The “/B” suffix denotes a hardware revision level within the 1756-CN2R product line. No functional segmentation of ControlNet redundancy logic is defined by the suffix beyond revision control and firmware alignment constraints.

Hardware Specifications

Backplane Bus Communication and ControlNet Deterministic Redundancy Behavior (Allen-Bradley ControlLogix Context)

The 1756-CN2R/B implements ControlLogix backplane arbitration logic for deterministic ControlNet scheduling, where A/B redundant channels maintain dual-path frame synchronization across scheduled and unscheduled communication segments. I/O data exchange timing is governed by chassis backplane scan cycles, with redundancy switching occurring at protocol level without interrupting scheduled connection states. Connection handling up to 100 simultaneous ControlNet links is managed through backplane-resident connection tables integrated with Logix controller task execution. The module supports hot-swappable insertion within active chassis without requiring full system shutdown, subject to backplane re-enumeration timing constraints.

Frequently Asked Questions (FAQ)

Q: Does the 1756-CN2R/B support hot-swap insertion in an energized ControlLogix chassis?
A: Yes. The module supports hot-swapping. Backplane re-initialization occurs after insertion, with temporary communication resynchronization across ControlNet connections.

Q: How is redundancy handled between ControlNet channels A and B?
A: Both channels operate in parallel with independent physical paths. Failover is handled at the communication layer without requiring controller task interruption.

Q: Does the module provide galvanic isolation between redundant channels?
A: No. Only basic insulation is specified between ControlNet interfaces and backplane; A/B channel separation does not include full galvanic isolation.

Field Installation Guidelines

• Install module only into compatible ControlLogix chassis backplane slot

• Ensure chassis power is removed before insertion when following conservative maintenance procedures

• Maintain separation between ControlNet coaxial routing and high-noise power conductors

• Use proper BNC termination for ControlNet segment ends to maintain impedance integrity

• Observe static discharge control during handling of backplane connectors

• Verify firmware compatibility with Logix controller and Studio 5000 configuration environment before commissioning

• Do not bend coaxial cables below minimum radius to avoid signal attenuation on ControlNet segments