Allen-Bradley 1756-CNB/D ControlNet Bridge Module | ControlLogix Platform
Engineering Background
The Allen-Bradley 1756-CNB/D is a ControlNet Bridge module designed for the ControlLogix chassis. It enables deterministic, high-speed communication between ControlLogix controllers and ControlNet I/O, drives, and peer controllers across a coaxial or fiber ControlNet network. As a Series D revision, this module incorporates firmware and hardware refinements that improve network stability and diagnostic depth compared to earlier revisions.
Product Positioning
Targeted at process, hybrid, and discrete manufacturing environments where scheduled, time-critical data exchange is mandatory, the 1756-CNB/D serves as the backbone bridge between the ControlLogix backplane and the ControlNet fieldbus. It is the preferred choice for engineers maintaining or expanding legacy ControlNet architectures and for system integrators building new ControlLogix-based ControlNet cells.
Complete Technical Specifications
- Catalog Number: 1756-CNB/D
- Series / Revision: Series D
- Platform: ControlLogix (1756 chassis)
- Network Protocol: ControlNet (ANSI/ISA-S72.01, IEC 61158 Type 2)
- Network Topology: Coaxial trunk-and-drop; redundant media supported with 1756-CNBR/D
- Data Rate: 5 Mbps (fixed)
- Max Nodes per Network: 99 (addresses 1–99)
- Scheduled Connections: Up to 64 scheduled connections
- Unscheduled Connections: Up to 64 unscheduled connections
- 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: 5–95% non-condensing
- Vibration: 2 g @ 10–500 Hz (IEC 68-2-6)
- Shock: 30 g operational; 50 g non-operational
- Dimensions (H × W × D): 147 mm × 45 mm × 144 mm (5.79 × 1.77 × 5.67 in)
- Weight: Approx. 1,200 g (module only)
- Certifications: UL Listed, CE Marked, C-Tick, FM Class I Div 2
- Firmware: Field-upgradeable via RSLogix 5000 / Studio 5000
- Enclosure Rating: Open-type (chassis-mounted)
Proven Application Environments
- Automotive Assembly: Synchronizing robot controllers and conveyor drives over a deterministic ControlNet segment within a ControlLogix cell.
- Oil & Gas Processing: Bridging ControlLogix controllers to remote ControlNet I/O racks in hazardous-area enclosures (Class I Div 2 rated).
- Water & Wastewater: Connecting distributed pump stations and valve actuators across long-distance ControlNet coaxial runs.
- Pharmaceutical Manufacturing: Providing scheduled, auditable data exchange between batch controllers and ControlNet-connected weigh modules.
- Power Generation: Integrating ControlLogix-based turbine control systems with ControlNet-connected protection relays and HMI panels.
- Material Handling: Coordinating high-speed sortation systems where deterministic scan times are critical to throughput.
Engineering Advantages
- Deterministic Scheduling: ControlNet’s CTDMA media access guarantees scheduled data delivery within a defined Network Update Time (NUT), eliminating jitter-related faults in time-critical loops.
- Dual-Media Redundancy (with 1756-CNBR/D): Supports redundant coaxial cable paths; automatic failover with no data loss on media break.
- Transparent Backplane Integration: Appears as a standard 1756 module; configured entirely within RSLogix 5000 / Studio 5000 without separate network configuration software beyond RSNetWorx for ControlNet.
- Rich Diagnostics: Onboard LED indicators (NET, OK, LINK) plus detailed fault codes accessible via the controller’s I/O tree for rapid fault isolation.
- Scalable Node Count: Supports up to 99 nodes per network segment, accommodating large distributed I/O architectures without additional bridges.
- Series D Enhancements: Improved EMI immunity and refined firmware for more stable NUT negotiation compared to Series A/B/C revisions.
System Architecture & Signal Flow
The 1756-CNB/D occupies one slot in the 1756 ControlLogix chassis and communicates with the ControlLogix controller via the high-speed backplane bus. On the network side, a BNC or N-type coaxial connector interfaces to the ControlNet trunk cable. The module acts as a bridge: it maps I/O data from remote ControlNet nodes (1794-ACN15, 1756-CNB peers, PowerFlex drives, etc.) into the controller’s I/O tree as produced/consumed tags. Scheduled connections are configured in RSNetWorx for ControlNet, which programs the NUT and connection parameters into the module’s non-volatile memory. Unscheduled (explicit messaging) connections handle configuration and diagnostic traffic without consuming scheduled bandwidth.
Typical Signal Flow:
- ControlLogix controller writes output data to backplane.
- 1756-CNB/D reads backplane data and transmits scheduled ControlNet frames at the configured NUT.
- Remote ControlNet nodes receive frames, update outputs, and return input data in the next scheduled interval.
- 1756-CNB/D writes received input data back to the backplane for the controller to consume.
Sourcing & Quality Verification
- Source: Verified surplus and authorized-channel stock; no counterfeit or refurbished units.
- Inspection Protocol: Each unit undergoes visual inspection (PCB, connectors, label integrity), firmware version verification, and powered functional test on a live ControlLogix chassis prior to shipment.
- Traceability: Lot records and inspection reports available upon request for regulated industries.
- Packaging: Anti-static bag + foam-lined carton; double-boxed for international freight.
- Warranty: 12-month Konmask operational warranty covering defects in materials and workmanship.
Procurement Process
- Inquiry: Submit your quantity and required delivery date via the product page or email support@konmask.com.
- Quote: Receive a formal quotation with unit price, lead time, and shipping options within 1 business day.
- Order Confirmation: Approve the quote; Konmask issues a proforma invoice.
- Payment: T/T bank transfer, PayPal, or credit card accepted.
- Shipment: DHL / FedEx / UPS express with full tracking; export documentation (commercial invoice, packing list, COO) included.
- After-Sales: Technical support available via email or WhatsApp (+86 198-5928-8691) for installation and commissioning queries.
Technical FAQ
Q: Is the 1756-CNB/D compatible with all ControlLogix chassis sizes?
A: Yes. It is compatible with all 1756 chassis (4-, 7-, 10-, 13-, and 17-slot) running ControlLogix firmware L55, L61, L62, L63, L71, L72, L73, L74, L75, L81, L82, L83, L84, L85 controllers.
Q: What is the difference between 1756-CNB/D and 1756-CNBR/D?
A: The 1756-CNBR/D adds redundant media support (two independent coaxial ports) for fault-tolerant ControlNet topologies. The 1756-CNB/D has a single coaxial port and is used in non-redundant media configurations.
Q: Can I use this module with Studio 5000 Logix Designer?
A: Yes. Studio 5000 Logix Designer (v21 and later) fully supports the 1756-CNB/D. RSNetWorx for ControlNet is still required to schedule the network NUT and configure connections.
Q: What ControlNet cable and tap specifications are required?
A: Use RG-6 quad-shield coaxial cable with 75 Ω impedance. Taps must comply with the ControlNet specification (e.g., Allen-Bradley 1786-TPS, 1786-TPR). Maximum trunk length is 1,000 m (3,280 ft) without repeaters.
Q: How do I verify the firmware revision on a received unit?
A: Connect the module to a live chassis, open RSLogix 5000 / Studio 5000, navigate to the module properties under the I/O tree, and check the Firmware Revision field. Konmask can provide the firmware version in the pre-shipment inspection report upon request.
Q: Is export licensing required for this product?
A: The 1756-CNB/D is classified as EAR99 under U.S. Export Administration Regulations for most destinations. Buyers are responsible for verifying import regulations in their jurisdiction. Konmask provides all standard export documentation.
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