Product Overview

The Allen-Bradley 1756-CNBR is a high-performance communication bridge designed to interface a ControlLogix® chassis with a ControlNet™ network. Distinguishing itself from standard interface modules, the 1756-CNBR is specifically engineered for high-availability systems, featuring dual BNC connectors to support redundant media. This allows for the implementation of two independent cable paths, ensuring that deterministic communication between controllers and distributed I/O remains uninterrupted even if one cable is severed or compromised.

This module serves a dual role in industrial architectures: it can function as a local communication adapter for a ControlLogix processor or as a remote head module in a distributed I/O rack. Operating at a data rate of 5 Mbps, it facilitates both scheduled messaging (interlocking and I/O control) and unscheduled messaging (configuration and diagnostics). By utilizing a Producer/Consumer network model, the 1756-CNBR ensures that critical control data is delivered with the precise repeatability required for synchronized motion and complex process applications.

Network Architecture and Redundancy

The 1756-CNBR is the cornerstone of a "fault-tolerant" ControlNet network. It manages up to 64 bidirectional connections and supports a maximum of 99 nodes on a single segment.

• Redundant Media Ports: Two BNC connectors (Channel A and Channel B) allow for parallel cabling using RG-6 quad-shield coax, providing a seamless failover mechanism.

• Network Access Port (NAP): An integrated RJ-45 port provides local access for configuration and programming without disturbing the primary network cabling.

• Deterministic Communication: Unlike standard Ethernet, this module ensures I/O data is transmitted at pre-defined intervals, making it suitable for safety and high-speed coordination.

• Capacity: Supports 40 to 48 logical communication connections and can buffer up to 20 unconnected messages simultaneously.

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Model Number: 1756-CNBR

• Module Type: ControlNet Bridge (Redundant)

• Communication Rate: 5 Mbps

• Nodes Supported: 99 (Maximum)

• Backplane Current (5.1V DC): 970 mA

• Backplane Current (24V DC): 1.7 mA

• Power Dissipation: 5.1 Watts

• Thermal Dissipation: 17.4 BTU/hr

• Isolation Voltage: 50V (Continuous)

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Weight: 0.25 kg (0.55 lbs)

• Dimensions: 17.0 x 13.0 x 3.2 cm

Installation and Reliability Features

• Chassis Flexibility: Compatible with all 1756 ControlLogix chassis (4, 7, 10, 13, and 17-slot variations) and power supplies.

• Alphanumeric Display: The front panel includes a scrolling 4-character display that provides real-time diagnostic codes and network status, facilitating rapid troubleshooting.

• Producer/Consumer Logic: Optimizes network bandwidth by allowing multiple controllers to consume the same data packet simultaneously.

• Rugged Construction: Built to withstand industrial shock and vibration, ensuring stable operation in heavy manufacturing and continuous process environments.