Product Overview

The Allen-Bradley 1756-CNB (specifically the current Series E revision, 1756-CNB/E) operates as a high-velocity communication bridge within the ControlLogix 1756 chassis ecosystem. This module links your central Logix processor to a dedicated 5 Mbps ControlNet network via robust 75-ohm coaxial cabling. By handling both scheduled, deterministic I/O traffic and unscheduled peer-to-peer messaging, this card establishes predictable, time-critical control links across sprawling manufacturing networks.

We deliver this product as a 100% Brand New, original factory-sealed unit in its native factory packing. Each module includes an authentic 12-month factory-backed warranty, ensuring pristine component status, zero runtime hours, and clean BNC interface ports for immediate installation.

Technical Specifications

Part Number Breakdown

While the base model remains the 1756-CNB, the letter suffix denotes manufacturing lifecycle enhancements and component revisions.

• 1756-CNB: Base model identifier for the ControlLogix ControlNet Coaxial Bridge.

• Suffix /E: Designates Series E hardware. This specific hardware layer includes updated internal microprocessors, optimized thermal profiles, and enhanced backplane transmission bandwidth compared to obsolete Series A, B, C, or D modules.

Engineering Advantages

• Enforce Deterministic System Response: Industrial networks often suffer from unpredictable data packet collisions. The 1756-CNB eliminates this variance by strictly managing Network Update Time (NUT) parameters, locking in guaranteed I/O refresh cycles for time-critical motion control and precise valve positioning.

• Establish True Media Redundancy: The dual-BNC architecture interfaces seamlessly with 1786-TPYR or 1786-TPSC Y-taps. By deploying two parallel coaxial trunk lines, the system maintains uninterrupted data routing even if a stray forklift or mechanical vibration severs one physical cable path.

• Defeat Extreme Electromagnetic Interference: Heavy variable frequency drives (VFDs) and high-voltage motor starters emit massive electromagnetic noise. The 1756-CNB utilizes heavy-duty quad-shield RG-6 coaxial connections combined with channel-to-backplane electrical isolation to shield network integrity from harsh ambient factory floor interference.

• Simplify Universal Chassis Placement: This bridge contains independent power management hardware, allowing engineers to slide the module into any available slot within a standard 1756 chassis. It shares data smoothly across the multi-master backplane without choking adjacent processor or I/O modules.

FAQs

• Can I replace an older Series D 1756-CNB module with this new Series E version?

  Yes. The 1756-CNB/E provides complete backward compatibility. It directly replaces previous Series A, B, C, and D variants inside existing ControlLogix architectures. You simply configure the matching slot location in your RSLogix 5000 or Studio 5000 hardware tree to resume operations.

• Does this module support fiber-optic ControlNet networks directly?

  No. The 1756-CNB features physical BNC connectors designed for 75-ohm quad-shield coaxial networks. If your plant routing requires fiber-optic segments to span long physical distances, you must connect the coaxial output of this card into an external 1786-RPFM fiber-optic repeater module.

• What is the difference between scheduled and unscheduled messaging on this card?

  Scheduled messaging reserves a precise slice of network bandwidth exclusively for interlocking data and real-time I/O status, guaranteeing execution times. Unscheduled messaging utilizes the remaining leftover bandwidth to execute non-critical tasks, such as uploading controller programs, altering recipes, or adjusting HMI parameters.