Allen-Bradley 1756-CNB/D ControlNet Bridge – ControlLogix Replacement

Product Overview

Allen-Bradley 1756-CNB/D ControlNet Bridge – ControlLogix Replacement & Upgrade Solution

The Allen-Bradley 1756-CNB/D ControlNet Bridge Module is a critical communication interface within the Rockwell Automation ControlLogix platform, enabling seamless data exchange between the ControlLogix backplane and a ControlNet network. As legacy installations age and Rockwell Automation progressively discontinues older firmware revisions, plant engineers and procurement teams face increasing pressure to source verified replacement units that maintain full backward compatibility with existing wiring, network topology, and PLC program logic.

At TOPNLMS, we stock the 1756-CNB/D as a direct drop-in replacement for earlier revisions including the 1756-CNB, 1756-CNB/A, and 1756-CNB/B. Each unit is sourced from authorized distribution channels, individually inspected, and shipped with a 12-month warranty. Whether you are managing a planned upgrade cycle or responding to an unplanned module failure, our inventory is ready to minimize your downtime.

Compatibility Comparison Table

Seamless Upgrade Solutions

A successful migration from an aging ControlNet architecture to a modernized ControlLogix system involves more than swapping a single bridge module. During the upgrade process, engineers typically address the entire communication chain. The 1756-CNB/D works in conjunction with the 1756-L71 or 1756-L73 ControlLogix controller, which serves as the program execution engine on the same backplane. Power to the chassis is supplied by the 1756-PA72 or 1756-PB72 power supply module, and the chassis itself — commonly a 1756-A10 ten-slot rack — houses all modules in a compact, DIN-rail or panel-mount enclosure.

On the I/O side, digital and analog field signals are typically wired through 1756-IB16 digital input modules and 1756-OF8 analog output modules, both of which remain fully compatible with the upgraded ControlNet bridge configuration. For installations that also require EtherNet/IP connectivity alongside ControlNet — a common requirement in hybrid migration projects — the 1756-EN2T EtherNet/IP bridge module can be installed in an adjacent slot without any conflict.

Where field devices communicate over DeviceNet rather than ControlNet, a 1756-DNB DeviceNet bridge module handles that protocol layer independently, allowing both networks to coexist on the same ControlLogix backplane. Programming and firmware updates are performed via a 1756-CP3 serial programming cable or directly over EtherNet/IP using Studio 5000 Logix Designer, eliminating the need for dedicated programming hardware in most retrofit scenarios.

For installations where signal isolation is required between field instruments and the ControlNet segment — particularly in high-noise industrial environments such as steel mills, chemical plants, or water treatment facilities — inline signal isolators and terminal block assemblies from the 1492-series wiring system provide a clean interface without modifying the existing cable runs. This end-to-end compatibility across the ControlLogix ecosystem is what makes the 1756-CNB/D the preferred replacement choice for system integrators managing multi-phase modernization projects.

Retrofit Guidance FAQ

Q: Do I need to re-terminate my ControlNet coaxial cables when replacing the 1756-CNB/B with the 1756-CNB/D?
No. The 1756-CNB/D uses the same BNC coaxial connector interface as all previous CNB revisions. Your existing RG-6 or RG-11 trunk cable and tap assemblies connect directly without any re-termination or new cable runs.

Q: Will my existing RSLogix 5000 or Studio 5000 project require modification?
In most cases, no. The 1756-CNB/D is recognized by Studio 5000 Logix Designer as a compatible replacement. You may need to update the module definition in your I/O tree if the firmware revision tag differs, but the underlying program logic, scheduled connections, and produced/consumed tags remain unchanged.

Q: How do I reconfigure the ControlNet network after module replacement?
Use RSNetWorx for ControlNet to verify the node address, NUT (Network Update Time), and scheduled connection parameters. The 1756-CNB/D retains the same node address configuration method via rotary switches on the module faceplate, so no software-only reconfiguration is required for a direct swap.

Q: Can the 1756-CNB/D coexist with a 1756-EN2T in the same chassis?
Yes. The ControlLogix backplane supports multiple communication bridge modules simultaneously. The 1756-CNB/D handles ControlNet traffic while the 1756-EN2T manages EtherNet/IP connections independently, with the controller arbitrating both networks through its connection manager.

Q: What is the physical installation space requirement?
The 1756-CNB/D occupies a single slot in any 1756-series chassis (1756-A4 through 1756-A17). No additional mounting hardware, DIN rail adapters, or panel cutouts are required beyond what the existing chassis already provides.

Q: Is the module compatible with redundant ControlNet topologies?
The 1756-CNB/D supports both single-media and dual-media (redundant) ControlNet configurations. For redundant installations, two 1756-CNB/D modules are installed in adjacent slots and configured as a redundant pair via RSNetWorx, providing automatic failover without program changes.

Warranty Assurance

Every 1756-CNB/D unit shipped by TOPNLMS is covered by a 12-month warranty from the date of delivery. Prior to shipment, each module undergoes a functional verification process that includes backplane communication testing, ControlNet port integrity checks, and firmware revision confirmation. Units that do not pass inspection are not shipped.

In the event of a warranty claim, TOPNLMS provides a replacement unit or full refund within the warranty period. Our after-sales response team is reachable via email at [email protected] or by phone at +86 18359293191. We support procurement teams with documentation including test reports, packing lists, and commercial invoices for customs clearance on international shipments.

Standard lead time for in-stock units is 1–3 business days for domestic China shipments and 5–10 business days for international express delivery. Expedited shipping options are available upon request. We accept T/T bank transfer, PayPal, and trade assurance payment terms for qualified buyers.