Allen-Bradley 1756-CN2R/B ControlNet Communication Module | Replacement, Equivalent & Selection Guide
The Allen-Bradley 1756-CN2R/B is a ControlNet communication module designed for the Rockwell Automation ControlLogix platform. It provides a high-speed, deterministic ControlNet network interface for real-time I/O control, peer-to-peer messaging, and controller-to-controller communication in demanding industrial automation environments. This guide covers technical specifications, compatible replacements, application scenarios, and sourcing information to help engineers and procurement teams make confident selection decisions.
Technical Specifications
- Part Number: 1756-CN2R/B
- Vendor / Brand: Allen-Bradley (Rockwell Automation)
- Series: ControlLogix 1756
- Network Protocol: ControlNet (IEEE 802.4 based)
- Redundant Media: Yes — dual coax BNC connectors (redundant ControlNet)
- Data Rate: 5 Mbps
- Max Nodes per Network: Up to 99 nodes
- Scheduled Connections: Supports scheduled (I/O) and unscheduled (messaging) traffic
- Backplane Current Draw: 1.0 A @ 5 VDC; 3.0 mA @ 24 VDC
- Power Dissipation: 5.1 W (max)
- Operating Temperature: 0 °C to 60 °C (32 °F to 140 °F)
- Storage Temperature: -40 °C to 85 °C
- Relative Humidity: 5% to 95% (non-condensing)
- Dimensions (H × W × D): 147 mm × 45 mm × 94 mm (approx.)
- Weight: ~250 g
- Certifications: UL, CE, cUL, C-Tick
- Firmware Revision: /B (Series B)
- Form Factor: Single-slot ControlLogix chassis module
Compatible Replacement & Equivalent Models
When the 1756-CN2R/B is unavailable or end-of-life, the following models may serve as functional replacements depending on your system configuration. Always verify firmware compatibility and network topology before substitution.
- 1756-CN2 / 1756-CN2/B — Single-media ControlNet module (non-redundant); drop-in replacement for non-redundant topologies
- 1756-CN2R/A — Earlier series revision; functionally equivalent, verify firmware version compatibility
- 1756-CN2RXT — Extended-temperature variant for harsh environments (−25 °C to 70 °C)
- 1756-CN3 — Newer generation ControlNet bridge module; check RSNetWorx compatibility
- 1756-CNBR — ControlNet bridge module for remote I/O bridging applications
- Third-party equivalents: Certain HMS Anybus and ProSoft Technology ControlNet gateways can bridge ControlNet to EtherNet/IP as a migration path — consult your system integrator for topology impact
Note: Konmask.com supplies both new and tested-surplus 1756-CN2R/B units. Contact us to confirm availability and revision.
Why Choose the Original 1756-CN2R/B
- Redundant Media Support: Dual coax ports provide fault-tolerant ControlNet communication — critical for continuous process and safety applications
- Deterministic Performance: ControlNet’s scheduled bandwidth guarantees cycle-accurate I/O updates, unlike standard Ethernet
- Proven Reliability: Widely deployed in automotive, oil & gas, water treatment, and discrete manufacturing since the early 2000s
- Native ControlLogix Integration: Seamless backplane communication with Logix5000 controllers (L6x, L7x, L8x series)
- RSNetWorx for ControlNet: Full support for Rockwell’s network scheduling and configuration tool
- Long Service Life: Robust industrial-grade design with extensive installed base and available spare parts
Typical Applications
- High-speed I/O control in automotive assembly lines
- Redundant ControlNet backbone in oil & gas processing facilities
- Controller-to-controller messaging in multi-PLC manufacturing cells
- Remote I/O communication in water and wastewater treatment plants
- Distributed control in food & beverage packaging lines
- Safety-critical process control where deterministic communication is mandatory
System Compatibility
- Compatible Controllers: All ControlLogix L6x, L7x, L8x series (e.g., 1756-L61, 1756-L71, 1756-L83E)
- Compatible Chassis: All 1756 ControlLogix chassis (4, 7, 10, 13, 17-slot)
- Compatible Power Supplies: 1756-PA72, 1756-PB72, 1756-PA75, and other standard ControlLogix PSUs
- Software: RSLogix 5000 / Studio 5000 Logix Designer; RSNetWorx for ControlNet (required for network scheduling)
- ControlNet Cable: RG-6 coaxial cable with BNC connectors; max segment length per ControlNet specification
- Not Compatible With: CompactLogix (1769) or SoftLogix platforms without an appropriate bridge
Selection Guide
Use the following criteria to determine whether the 1756-CN2R/B is the right module for your application:
- Need redundant ControlNet media? → Choose 1756-CN2R/B (this module) or 1756-CN2RXT for extended temperature
- Single-media ControlNet sufficient? → Consider 1756-CN2/B for lower cost
- Migrating to EtherNet/IP? → Evaluate 1756-EN2T / 1756-EN2TR as a long-term platform migration; note this requires network redesign
- Harsh environment (below 0 °C or above 60 °C)? → Specify 1756-CN2RXT
- Need ControlNet bridging to remote chassis? → Evaluate 1756-CNBR
- Budget-constrained replacement? → Tested-surplus 1756-CN2R/B or /A units from Konmask.com offer significant cost savings with functional equivalence
Quality Assurance & Sourcing
- Source: Konmask.com sources 1756-CN2R/B modules from authorized distributors and verified surplus channels
- Inspection: All surplus units undergo visual inspection, firmware version verification, and functional power-on testing before shipment
- Authenticity: We do not supply counterfeit or remarked parts — provenance documentation available on request
- Warranty: 90-day functional warranty on tested-surplus units; new units carry standard Rockwell Automation warranty
- Lead Time: In-stock units ship within 1–3 business days; contact us for bulk order lead times
- Export Compliance: Orders subject to applicable export control regulations (EAR/ECCN); end-user declaration may be required
How to Order
- Part Number: 1756-CN2R/B
- Specify: Quantity, required firmware revision (if critical), and whether new or tested-surplus is acceptable
- Request a Quote: Email support@konmask.com or call +0086 19859288691
- Payment: T/T (wire transfer), PayPal, and other methods available — contact us for details
- Shipping: DHL, FedEx, UPS international express; local courier options for domestic CN orders
- Documentation: Commercial invoice, packing list, and test report provided with each shipment
Replacement & Compatibility FAQ
Q: Can I replace a 1756-CN2R/A with a 1756-CN2R/B?
A: Yes, in most cases. The /B revision is backward compatible. Verify that your RSNetWorx schedule and controller firmware support the /B revision — a re-scheduling of the ControlNet network may be required after module swap.
Q: Is the 1756-CN2R/B compatible with ControlLogix L8x (v30+ firmware) controllers?
A: Yes, the 1756-CN2R/B is supported on L8x controllers. Confirm the module firmware revision is compatible with your controller’s Logix firmware version via Rockwell’s Product Compatibility and Download Center (PCDC).
Q: Can I use the 1756-CN2R/B in a single-media (non-redundant) ControlNet topology?
A: Yes. You can connect only one coax port and leave the second unused. The module will operate in single-media mode.
Q: What is the difference between 1756-CN2R/B and 1756-CN3?
A: The 1756-CN3 is a newer generation module with updated firmware and improved diagnostics. Both support redundant ControlNet media. The CN3 may require updated RSNetWorx versions. For legacy systems, the CN2R/B is often preferred for direct replacement.
Q: Is the 1756-CN2R/B still in production?
A: Rockwell Automation has moved toward EtherNet/IP as the preferred network. The 1756-CN2R/B may be in a mature/limited availability phase. Konmask.com maintains surplus stock to support ongoing maintenance needs — contact us for current availability.
Q: Can Konmask.com provide a certificate of conformance or test report?
A: Yes. Test reports and certificates of conformance are available for tested-surplus units upon request.
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Original Source: https://Konmask.com
Contact: support@konmask.com | +0086 19859288691
