Allen Bradley 1756-CNB | 5 Mbps ControlNet Interface

Description

Note: Many products are not yet listed. Please contact us for more product information. Our supply channels are constantly expanding, and we currently have 20 stable shared supply channels. Please confirm the model, product, price, and all other necessary information with customer service before placing an order. We offer new, refurbished, and used products, and prices are adjusted according to the year of the item you require.

Key Technical Specifications

The 1756-CNB is the standard, nonredundant ControlNet bridge. For redundant ControlNet media, the corresponding module is the 1756-CNBR, which has two BNC connectors.

Product Introduction

The Allen-Bradley 1756-CNB is a ControlNet Bridge Module designed for the ControlLogix 1756 automation platform. It provides communication between ControlLogix controllers, remote I/O chassis, and other ControlNet-compatible devices over a 5 Mbps industrial network.

Supporting up to 99 network nodes and 64 connections, the module is used in distributed control architectures where deterministic communication between controllers and remote equipment is required. Its BNC network interface and NAP programming port support maintenance and network access in established ControlNet installations.

1756-CNB

1756-CNB

1756-CNB

1756-CNB

Application Scenarios & Field Experience

In distributed ControlLogix systems, remote I/O communication depends on a correctly configured ControlNet network. A failed bridge module can interrupt data exchange between the controller and remote chassis, potentially affecting multiple machines or process areas. During replacement, engineers need to check the network address, ControlNet schedule, connection configuration, and media topology. Matching the catalog number alone does not guarantee that the existing network will resume operation without configuration checks.

Typical application scenarios

1. Automotive Manufacturing — Connects ControlLogix controllers with remote I/O stations across production lines and assembly equipment.
2. Oil & Gas Processing — Supports ControlNet communication between central controllers and distributed process I/O cabinets.
3. Water Treatment — Exchanges control and status data between local PLC racks and remote pumping or treatment stations.
4. Power Generation — Provides network communication between ControlLogix controllers and distributed auxiliary equipment.

Illustrative engineering scenario, not a documented customer installation: A production facility experiences intermittent communication loss between a ControlLogix processor and a remote I/O chassis. Initial checks identify unstable network communication, and the maintenance team investigates the bridge module, cable connections, and network schedule. A replacement 1756-CNB is checked against the existing module revision and network configuration. After installation, the team verifies node communication, scheduled connections, and remote I/O data exchange before returning the equipment to operation.

Standard Operating Procedure (SOP) for Quality Control

1. Visual & Origin Inspection

• Verify the Allen-Bradley label, catalog number, serial number, and hardware series.
• Inspect the BNC connector, NAP port, backplane connector, and module housing.
• Check for corrosion, damaged contacts, cracks, or signs of unauthorized repair.
• Review available OEM packaging and origin documentation.

2. Functional Testing

• Where a compatible ControlLogix chassis and ControlNet test network are available, verify module startup and backplane communication.
• Check the module status and network status indicators.
• Verify communication through the BNC interface using compatible ControlNet equipment.
• Check node recognition and connection status.
• Where a suitable controller and remote I/O setup are available, verify data exchange between the processor and remote chassis.

3. Firmware & Configuration Verification

• Record the hardware series and firmware revision.
• Confirm compatibility with the ControlLogix processor and project configuration.
• Check the ControlNet node address and network schedule.
• Verify connection requirements and the configured network topology.
• Confirm whether the application requires standard or redundant ControlNet media. The 1756-CNB is not a substitute for the dual-BNC 1756-CNBR in a redundant media arrangement.

4. ESD-Safe Packaging

• Handle the module using appropriate electrostatic-discharge precautions.
• Protect the BNC connector, NAP port, and backplane connector.
• Use anti-static packaging and protective cushioning for transportation.

5. Pre-Shipment Documentation

• Provide actual product photos and a clear identification-label photo.
• Confirm the catalog number and hardware series.
• Provide available inspection records and test results for checks actually completed on the specific unit.

Frequently Asked Questions (FAQ)

Q1: Can the 1756-CNB replace the 1756-CNBR?
A: Not as a direct replacement in a redundant ControlNet media configuration. The 1756-CNB has one BNC connector for standard media operation, while the 1756-CNBR has two BNC connectors for redundant media. Confirm the existing network architecture before ordering.

Q2: What warranty do you provide for the 1756-CNB?
A: We offer a 12-month warranty, subject to confirmed order terms. Product condition and warranty coverage will be stated in the order confirmation.

Q3: Is the 1756-CNB available for immediate shipment?
A: Stock availability and condition must be confirmed before ordering. For confirmed available stock, our usual arrangement is shipment within one week after payment. Product photos and live video inspection can be arranged before shipment.

Q4: Does firmware compatibility matter when replacing a 1756-CNB?
A: Yes. Check the module’s firmware revision, hardware series, ControlLogix processor compatibility, and ControlNet configuration. A replacement module may require network and project verification before it can communicate correctly with existing devices.

Q5: What should engineers check before installing the replacement?
A: Record the original node address, network schedule, cable connections, and module revision. Confirm that the network is designed for standard rather than redundant media. Follow the approved shutdown and network maintenance procedures, and verify remote I/O communication before restoring normal operation.

Lifecycle note: Rockwell Automation lists the 1756-CNB as discontinued effective December 31, 2024, and identifies the 1756-CN2 as its engineering replacement. The 1756-CN2 is a replacement option requiring system compatibility assessment, not an automatic plug-in substitute.