Allen-Bradley 1756-CN2R ControlLogix Communication Module – Obsolete ControlLogix Spare Part

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756-CN2R ControlLogix Communication Module – Obsolete ControlLogix Spare Part

RFQ support for obsolete parts: Send the model number, required quantity and destination so DriveKNMS can confirm sourcing options before quotation.

Technical Specifications

Solving the Discontinued Hardware Crisis

Rockwell Automation officially discontinued the 1756-CN2R as part of its broader migration push toward EtherNet/IP. For facilities that built their automation architecture on ControlNet in the 1990s and 2000s — particularly in automotive body shops, chemical batch processing, and water treatment — this discontinuation creates a structural vulnerability. The 1756-CN2R handles scheduled and unscheduled messaging between ControlLogix controllers and ControlNet I/O adapters. There is no firmware patch, no software workaround, and no drop-in EtherNet/IP substitute that does not require a full network re-architecture.

Plants running Rockwell's ControlNet-based systems — including those integrated with legacy SCADA platforms and third-party DCS bridges — face a hard reality: when this module fails and no spare exists, the line stops. The question is not whether to source a spare. The question is whether to source it before or after an unplanned outage.

Condition & Reliability Assurance

Every 1756-CN2R unit processed by DriveKNMS undergoes a structured 5-step quality verification protocol before it is offered for sale:

• Step 1 – Electrolytic Capacitor Inspection: Capacitor aging is the primary failure mode in modules of this vintage. Each unit is inspected for bulging, leakage, and ESR deviation. Units with degraded capacitors are either recapped or rejected.
• Step 2 – Firmware Version Verification: The installed firmware revision is confirmed and documented. Compatibility with the target ControlLogix controller firmware is verified prior to shipment where customer system information is provided.
• Step 3 – Connector and Pin Corrosion Audit: Backplane edge connectors and ControlNet coax ports are inspected under magnification for oxidation, pin deformation, and contact resistance anomalies.
• Step 4 – Functional Communication Test: Where test bench infrastructure permits, modules are powered and ControlNet communication is verified against a known-good ControlLogix chassis.
• Step 5 – Packaging and ESD Protection: Units are packaged in anti-static bags with desiccant and rigid outer packaging to prevent transit damage and moisture ingress.

Condition grades (New Surplus, Refurbished, or Used-Tested) are disclosed on each order confirmation. No unit is shipped without a documented condition grade.

Key Features for System Maintenance

• Drop-in replacement: The 1756-CN2R installs directly into any open 1756 chassis slot. No hardware modification to the chassis or backplane is required.
• No PLC reprogramming required: The module retains its ControlNet node address configuration. Replacing a failed unit does not require changes to the RSLogix 5000 / Studio 5000 project file in most standard configurations.
• No network redesign: ControlNet topology, scheduled bandwidth allocation, and NUT (Network Update Time) settings are preserved. The replacement module joins the existing network without disrupting other nodes.
• Avoids engineering re-architecture costs: Migrating from ControlNet to EtherNet/IP requires new I/O adapters, new cabling infrastructure, controller firmware updates, and full Factory Acceptance Testing. A spare 1756-CN2R eliminates this cost for the duration of the asset's planned operational life.