Allen-Bradley 1756-CNBR/E ControlNet Redundant Communication Module

The Allen-Bradley 1756-CNBR/E, also cataloged as the 1756-CNBR ControlNet redundant communication module, serves as the primary communication interface for dual-channel ControlNet networking across ControlLogix platforms. It provides direct physical layer execution for redundant A/B ControlNet data paths, supporting deterministic scheduled and unscheduled message exchange between controllers and distributed nodes.

Suffix Breakdown & Model Matrix

• 1756: ControlLogix chassis platform identifier

• CNBR: ControlNet redundant bridge communication module designation

• /E: Hardware revision level indicator within the CNBR series

No additional functional segmentation is defined beyond platform family and revision suffix.

Hardware Specifications

Redundant ControlNet Channel Execution and Backplane Behavior

The module implements dual independent ControlNet channels (A/B) for fault-tolerant deterministic communication. Both channels operate in parallel with synchronized network scheduling to maintain continuity of scheduled and unscheduled data transfer.

Backplane integration is executed through the 1756 chassis communication bus, with module-level arbitration managing connection instances up to 100 simultaneous links. Channel monitoring logic maintains link status and triggers failover behavior at the network interface layer without requiring controller intervention.

Electromagnetic immunity design supports operation under defined industrial field strengths, ensuring signal integrity across redundant coaxial ControlNet media paths.

Frequently Asked Questions (FAQ)

Q: Does the 1756-CNBR/E support simultaneous operation of both ControlNet channels?
A: Yes. Both A and B channels operate in parallel, with synchronization handled internally for redundancy and continuous communication.

Q: What happens if one ControlNet channel fails?
A: The module continues operation on the remaining channel while reporting channel fault status through diagnostic registers and controller feedback.

Q: Is the module hot-swappable during chassis operation?
A: Yes. It supports hot replacement within a ControlLogix chassis, but communication re-establishment depends on network rescheduling and connection recovery.

Field Installation Guidelines

The module shall be installed in a compatible ControlLogix 1756 chassis slot with controlled insertion into the backplane connector. Power cycling is recommended unless hot-swap procedures are explicitly supported by system configuration.

ControlNet A/B coaxial cables must be routed with physical separation to reduce correlated interference risk. Proper 75 ohm termination must be verified at network endpoints to maintain signal integrity.

Shielding shall be grounded at a single-point earth reference to prevent loop currents across redundant paths. All cabling must comply with ControlNet topology requirements including trunk/drop length constraints and connector torque specifications defined by system standards.