Allen-Bradley 1756-CNBR ControlNet Bridge Module

Allen-Bradley 1756-CNBR ControlNet Redundant Media Bridge Module

Product Introduction

The Allen-Bradley 1756-CNBR is a ControlNet communication module for ControlLogix systems. This module serves as a bridge between the ControlLogix backplane and ControlNet networks. What makes the 1756-CNBR unique is its redundant media support. It features two BNC ports instead of one.

Additionally, this module handles both scheduled and unscheduled data. It works with Logix5550 controllers to manage real-time I/O. The 1756-CNBR also bridges unscheduled messages between devices. This makes it essential for distributed I/O architectures.

Technical Specifications

Communication Features
ControlNet communication rate is 5 Mbps. The module supports 40-48 Logix communication connections. Maximum connections reach 64 total. Maximum number of nodes on the network is 99.

Port Configuration
The 1756-CNBR includes three ports total:

• Two (2) ControlNet BNC ports for redundant media

• One (1) Network Access Port (NAP) with RJ-45 8-pin shielded connector

The dual BNC ports enable redundant ControlNet media. If one trunk line fails, communication continues through the second path. This redundancy prevents communication loss during cable disconnection.

Power Requirements
Backplane current at 5.1 Volts DC draws 970 milliamps. Backplane current at 24 Volts DC draws 1.7 milliamps. Maximum power dissipation is 5.5 Watts. Thermal dissipation measures 17.4 BTU/hour.

Isolation and Enclosure
Isolation voltage rating is 30 Volts continuous. Enclosure type is open.

Physical and Environmental Data

Dimensions and Weight
Dimensions measure 5.51 x 4.41 x 5.71 inches. Slot width is 1. Weight equals 0.64 lbs (0.293 kg).

Temperature Rating
Operating temperature ranges from 32°F to 140°F (0°C to 60°C).

Compatible Chassis
The 1756-CNBR fits in these ControlLogix chassis:

• 1756-A4

• 1756-A7

• 1756-A10

• 1756-A13

• 1756-A17

Compatible Power Supplies
Standard power supply options include:

• 1756-PA72/C

• 1756-PA75/B

• 1756-PB72/C

• 1756-PB75/B

• 1756-PC75/B

• 1756-PH75/B

Redundant power supply options include:

• 1756-PA75R

• 1756-PB75R

• 1756-PSCA2

Communication Cable Requirements

Use 1786-RG6 quad shield RG6 coaxial cable for trunk connections. Connect to the trunk cable using ControlNet taps. Before making connections, check the tap drop cable label. This label indicates the attached segment. Proper labeling prevents accidental reversal of tap connections. Reversed connections cause incorrect status display and require troubleshooting.

Installation Guidelines

First, ensure chassis power is off. Install the 1756-CNBR into any available slot. The module requires only one slot. Next, connect the ControlNet BNC ports to your redundant network. Use proper 1786-RG6 cable and taps.

Furthermore, use the NAP port for local programming. Connect a standard Ethernet cable to your computer. Configure network parameters using Studio 5000 software. Finally, verify both redundant paths are working. Check module status indicators for proper operation.

Local vs. Distributed Installation

You can install the 1756-CNBR in two ways. First, as a local communication module alongside the ControlLogix processor. Second, as a head communication module in a distributed I/O rack. Both configurations work reliably.

Packaging List

• 1 x Allen-Bradley ControlLogix ControlNet bridge module (1756-CNBR)

• 1 x Module with dual BNC ports and NAP port

• 1 x Anti-static protective bag

• 1 x Factory cardboard box

Shipping Information

All orders ship via FedEx, UPS, or DHL. Delivery typically takes 3 to 7 business days.

Frequently Asked Questions (FAQ)

1. What is the difference between 1756-CNB and 1756-CNBR?
The 1756-CNBR has two ControlNet BNC ports for redundant media. The standard 1756-CNB has only one BNC port. Both modules have one RJ-45 NAP port.

2. Can I use the 1756-CNBR without redundant media?
Yes, you can use only one BNC port in simplex mode. The second port remains unused. However, you lose the redundancy benefit.

3. How many connections does the 1756-CNBR support?
The module supports 40-48 Logix communication connections. Maximum total connections reach 64 including scheduled and unscheduled types.

4. What cable is required for ControlNet connections?
Use 1786-RG6 quad shield RG6 coaxial cable. Standard RG6 cable is not sufficient. Always use Allen-Bradley approved ControlNet cable.

5. Does the 1756-CNBR work with any ControlLogix chassis?
Yes, it works with all standard ControlLogix chassis. Compatible models include 1756-A4, A7, A10, A13, and A17. The module occupies only one slot.