Allen-Bradley 1756-CN2R ControlLogix ControlNet Communication Module | Replacement, Equivalent & Selection Guide
The Allen-Bradley (AB) 1756-CN2R is a redundant ControlNet communication module designed for use within the Rockwell Automation ControlLogix platform. It provides deterministic, high-speed communication across ControlNet networks and supports redundant media configurations for mission-critical industrial applications. This page serves as a comprehensive selection, replacement, and compatibility reference for engineers and procurement teams.
Technical Specifications
- Part Number: 1756-CN2R
- Manufacturer: Allen-Bradley / Rockwell Automation
- Platform: ControlLogix (1756 chassis)
- Network: ControlNet (redundant media)
- Communication Rate: 5 Mbps
- Ports: 2 × BNC (coaxial, redundant)
- Max Nodes per Network: 99
- Scheduled Connections: Up to 64
- Unscheduled Connections: Up to 64
- Backplane Current Draw: 1.0 A @ 5 VDC
- Power Dissipation: 5.0 W
- Operating Temperature: 0 °C to 60 °C
- Storage Temperature: -40 °C to 85 °C
- Relative Humidity: 5% to 95% (non-condensing)
- Certifications: UL, CE, C-Tick, ATEX (Zone 2)
- Form Factor: Single-slot ControlLogix module
- Firmware: Field-upgradeable via RSLogix 5000 / Studio 5000
Compatible Replacement & Equivalent Models
When the 1756-CN2R is unavailable or end-of-life in your region, the following models may serve as functional replacements or equivalents depending on your system architecture:
- 1756-CN2 — Non-redundant ControlNet module; suitable for single-media ControlNet networks where redundancy is not required.
- 1756-CN2RXT — Extended-temperature variant of the 1756-CN2R; for harsh environments (−25 °C to 70 °C).
- 1756-CNBR — ControlNet bridge module; used for bridging between ControlNet segments in larger topologies.
- 1756-EN2T / 1756-EN2TR — EtherNet/IP communication modules; consider as a network migration path from ControlNet to Ethernet.
- 1756-EN3TR — Dual-port EtherNet/IP module with DLR support; modern replacement for redundant communication needs.
Note: Always verify firmware compatibility and I/O tree configuration before substituting modules in a live system.
Why Choose the Original 1756-CN2R
- Deterministic Communication: ControlNet’s scheduled bandwidth guarantees cycle-time consistency critical for motion and safety applications.
- Redundant Media: Dual BNC ports allow coaxial cable redundancy, eliminating single points of failure on the network layer.
- Proven Reliability: Deployed globally in automotive, oil & gas, water treatment, and discrete manufacturing for over two decades.
- Native ControlLogix Integration: Seamless configuration via Studio 5000 Logix Designer with no third-party drivers required.
- Backward Compatibility: Supports legacy PLC-5 and SLC 500 bridging via ControlNet, protecting existing infrastructure investments.
Typical Applications
- Automotive assembly line control with deterministic I/O scanning
- Oil & gas pipeline SCADA and remote I/O communication
- Water and wastewater treatment plant automation
- Redundant process control in chemical and pharmaceutical plants
- High-availability discrete manufacturing cells
- Legacy system integration bridging ControlNet to newer EtherNet/IP architectures
System Compatibility
- Chassis: All 1756 ControlLogix chassis (4, 7, 10, 13, 17-slot)
- Power Supplies: 1756-PA72, 1756-PB72, 1756-PA75, 1756-PB75, and compatible variants
- Controllers: All 1756-Lxx ControlLogix controllers (L61, L62, L63, L71, L72, L73, L83E, etc.)
- Software: RSLogix 5000 v16+, Studio 5000 Logix Designer v21+
- Network Topology: Coaxial bus, star (via repeaters), tree
- Remote I/O: Compatible with 1794 FLEX I/O, 1734 POINT I/O, and 1756 remote chassis via ControlNet adapters
Selection Guide
Use the following criteria to determine whether the 1756-CN2R is the right module for your application:
- Need redundant ControlNet media? → Choose 1756-CN2R (this module).
- Single-media ControlNet only? → Consider 1756-CN2 for lower cost.
- Harsh environment (below 0 °C)? → Specify 1756-CN2RXT.
- Migrating to EtherNet/IP? → Evaluate 1756-EN2TR or 1756-EN3TR as a long-term replacement.
- Bridging multiple ControlNet segments? → Use 1756-CNBR in conjunction.
- Existing ControlNet infrastructure to preserve? → Retain 1756-CN2R; it remains the most compatible option for existing coaxial networks.
Quality Assurance & Sourcing
- All modules sourced through authorized distribution channels or verified surplus with full traceability documentation.
- Each unit undergoes visual inspection, label verification, and functional pre-shipment testing where applicable.
- Counterfeit-risk screening applied to all surplus stock per industry best practices.
- Original factory packaging and firmware version documented upon request.
- Certificate of Conformance (CoC) and test reports available for qualified orders.
How to Order
- Part Number: 1756-CN2R
- Manufacturer: Allen-Bradley / Rockwell Automation
- Add to cart directly, or contact us for volume pricing, lead time confirmation, or export documentation.
- Expedited shipping available for urgent MRO and production-down situations.
- OEM and system integrator accounts welcome — request a trade account for net terms.
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Replacement & Compatibility FAQ
Q: Can I replace a 1756-CN2R with a 1756-CN2 without reconfiguring my network?
A: Functionally yes for single-media networks, but you will lose redundant media capability. Update the module configuration in Studio 5000 after swapping.
Q: Is the 1756-CN2R still in production?
A: Rockwell Automation has announced migration paths toward EtherNet/IP. Availability may vary by region. Contact us to confirm current stock and lead times.
Q: Can the 1756-CN2R coexist with EtherNet/IP modules in the same chassis?
A: Yes. Multiple communication modules of different network types can occupy the same ControlLogix chassis simultaneously.
Q: What cable type does the 1756-CN2R use?
A: RG-6 coaxial cable with BNC connectors per the ControlNet specification. Fiber-optic repeaters can extend distance.
Q: Do you provide firmware upgrade support?
A: We can advise on firmware compatibility. Firmware flashing must be performed by a qualified engineer using Rockwell-licensed software.
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