The 1756-CNBR is a legacy redundant ControlNet communication bridge module for the Allen‑Bradley ControlLogix chassis family, manufactured by Rockwell Automation. It serves as the interface between the ControlLogix backplane and a redundant ControlNet industrial network, delivering deterministic, fault-tolerant real-time communication for distributed I/O, peer-to-peer controller messaging, HMI polling and scheduled process control traffic. This module has been officially discontinued by Rockwell Automation, with the 1756-CN2R designated as its direct engineering replacement, making the 1756-CNBR highly sought-after for legacy plant maintenance, spare part stocking and retrofit projects where existing ControlNet infrastructure cannot be upgraded immediatelyRockwell A….

Designed with dual BNC ControlNet ports for redundant media, the 1756-CNBR supports automatic media failover. If one ControlNet trunk, tap or coaxial cable path fails, the second channel seamlessly takes over communication without halting scheduled control logic. This media redundancy is critical for continuous process industries including oil and gas, power generation, chemical processing, water and wastewater, pulp and paper, and other facilities where unplanned network downtime creates substantial production and safety risks. It operates at the fixed ControlNet speed of 5 Mbps and uses standard 1786‑RG6 quad-shielded coaxial trunk and tap cabling.

The 1756-CNBR provides 40 to 48 CIP connections, a key distinction compared to its successor 1756-CN2R which supports up to 100 connections. It also includes an onboard NAP (Network Access Port) RJ45 connector, allowing technicians to connect programming terminals directly to the ControlNet network via a 1786‑CP cable for online edits, firmware updates, diagnostics and tag monitoring without disrupting the main trunk wiring. The module consumes approximately 5.1 W of backplane power and occupies a single standard slot inside any ControlLogix chassis, compatible with a wide range of ControlLogix 5550 and early 5570 controllers, subject to firmware and series compatibility rules for redundant chassis pairsRockwell A….

Configuration and network scheduling for the 1756-CNBR are completed using RSNetWorx for ControlNet. Proper network scheduling is required to reserve bandwidth for scheduled I/O and inter-controller produced/consumed tags, preserving the deterministic timing that ControlNet is known for. Unscheduled messaging handles non-time-critical tasks such as program upload and download, alarm retrieval and diagnostic data collection. It interoperates with the full ControlNet ecosystem: Flex I/O adapters, PanelView HMIs, variable speed drives, third-party ControlNet-certified field devices and other ControlLogix communication modules.

Front-panel LED indicators give fast visual status for backplane activity, Channel A and Channel B network health, module run status and fault conditions. Common visible alarms include duplicate node addresses, trunk disconnection, backplane bus errors and module hardware faults, reducing troubleshooting time during plant outages. Series D and Series E hardware revisions have different compatibility rules for ControlLogix redundant controller systems; Series D units support older redundant firmware revisions, while Series E requires later Logix firmware versions, and they are not interchangeable without careful verificationRockwell A….

Typical use cases for the 1756-CNBR include emergency spare replacement for running legacy ControlNet systems, maintaining older redundant ControlLogix chassis pairs, matching existing module types during partial plant upgrades, and supporting brownfield automation projects where full migration to newer network topologies is scheduled for a later shutdown. Since original factory new stock is no longer available, most available units are surplus new, open-box, fully tested refurbished or used working pull units. All refurbished 1756-CNBR modules should undergo complete backplane communication testing, dual-port redundancy failover testing, firmware reset and LED verification before installation.

When sourcing the 1756-CNBR, buyers must confirm series, firmware revision, and compatibility with their existing ControlLogix controller and redundant configuration. If a direct drop-in replacement with higher connection capacity is acceptable, the 1756-CN2R is Rockwell’s official replacement, but migration will require engineering review of network schedules and connection count limits. We stock inspected 1756-CNBR spare modules for legacy automation maintenance, alongside other ControlLogix ControlNet communication modules, I/O cards, power supplies and controllers, with worldwide shipping and pre-sales compatibility checks for your existing ControlNet network layout.

Key technical highlights of 1756-CNBR:

• Brand: Allen‑Bradley (Rockwell Automation)
• Catalog number: 1756-CNBR
• Product type: Legacy ControlNet Redundant Bridge Module
• Compatibility: ControlLogix chassis, 5550 / early 5570 controllers
• ControlNet ports: Dual redundant BNC ports (Channel A / B)
• Auxiliary port: NAP RJ45 programming port
• Network speed: 5 Mbps ControlNet
• CIP connections: 40–48 connections
• Power consumption: 5.1 W
• Mounting: Single-slot ControlLogix chassis installation
• Configuration software: RSNetWorx for ControlNet, Studio 5000
• Lifecycle: Discontinued since Dec 31, 2024
• Official replacement: 1756-CN2R
• Application: Legacy redundant process control, distributed I/O, inter-PLC communication

1756-CN2R