Description
The Allen-Bradley 1756-CNBR is a high-performance communication module designed to bridge the ControlLogix backplane with a ControlNet network. This 1756-CNBR module provides high-speed, deterministic data exchange for mission-critical applications, supporting both redundant and non-redundant media configurations. It functions as a gateway for peer-to-peer communication between controllers and manages distributed I/O across the network, ensuring that time-critical control data is transmitted with repeatable latency and high reliability in complex industrial architectures.
Technical Specifications
- Model Number: 1756-CNBR
- Network: ControlNet (Redundant Media)
- Communication Rate: 5 Mbps
- Logix Connections: 64 to 128 (depending on firmware)
- Net throughput: 400 – 500 messages per second
- Backplane Current (5.1V DC): 970 mA
- Backplane Current (24V DC): 1.7 mA
- Power Dissipation: 5.14 Watts
- Operating Temperature: 0°C to +60°C
- Slot Width: 1 (Single Slot) Equipped with dual BNC connectors for media redundancy, this module allows for continuous system operation even if one trunk cable is compromised, making it an essential component for high-availability process control systems.
ALLEN BRADLEY 1756-CNBR
ALLEN BRADLEY 1756-CNBR
Model Comparison
The primary difference between the 1756-CNBR and the standard 1756-CNB is the “R” designation, which stands for Redundancy. While the 1756-CNB features a single ControlNet port, the 1756-CNBR features dual BNC ports to support a secondary physical cable path. Compared to newer Ethernet/IP modules like the 1756-EN2TR, the 1756-CNBR utilizes a deterministic scheduled bandwidth approach, which is often preferred in legacy systems or specific motion-control environments where precise timing is more critical than raw data throughput.
Operational Tips
- Redundant Media Wiring: For true redundancy, ensure Channel A and Channel B are routed through different physical paths to minimize the risk of simultaneous cable damage.
- Firmware Matching: In a redundant ControlLogix chassis pair, the 1756-CNBR firmware must be identical across both the primary and secondary chassis to ensure seamless switchover.
- Network Scheduling: Remember that any changes to the I/O configuration on a ControlNet network require the network to be re-scheduled using RSNetWorx for ControlNet.
- BNC Connection: Ensure that unused BNC ports are properly terminated with 75-ohm resistors if they are not part of an active redundant loop to prevent signal reflection.
