The Allen-Bradley 1756-CNBR is a ControlNet redundant communication bridge module used in the ControlLogix PLC system from Rockwell Automation. It provides high-speed, deterministic communication over the ControlNet network and supports dual-redundant media paths to improve system reliability and fault tolerance.
Compared with the standard CNB/CNB module, the CNBR is designed for applications where network redundancy is required to prevent communication loss due to cable or trunk failure.
It is widely used in mission-critical industrial systems such as power generation, oil & gas, petrochemical plants, and large-scale manufacturing automation.
Technical Specifications
| Parameter | Details |
|---|---|
| Product Type | ControlNet Redundant Bridge Module |
| Model | 1756-CNBR |
| System Compatibility | Allen-Bradley ControlLogix |
| Network Type | ControlNet |
| Communication Speed | 5 Mbps |
| Channels | 2 ControlNet ports (redundant media A/B) |
| Data Transfer | Scheduled & unscheduled messaging |
| Max Nodes | 99 nodes |
| Max Connections | ~40–48 Logix connections |
| Backplane Interface | ControlLogix chassis backplane |
| Power Consumption | ~5–6 W |
| Isolation Voltage | 30 V continuous |
| Installation Type | Chassis slot-mounted module |
| Operating Temperature | 0°C to 60°C |
The module is designed to support redundant coaxial ControlNet networks, ensuring continuous communication even if one media path fails.
Physical Dimensions & Weight
- Dimensions (H × W × D): 55 mm × 218 mm × 181 mm
- Weight: ~0.39 kg
The compact single-slot design allows installation in standard ControlLogix chassis systems.
Function in ControlLogix System
The 1756-CNBR is used to:
- Provide redundant ControlNet communication (dual media paths)
- Enable deterministic real-time I/O data exchange
- Support scheduled and unscheduled messaging
- Prevent communication loss from trunk or tap failure
- Connect distributed I/O and controllers in ControlNet systems
- Improve network reliability in critical automation systems
Recommended Related Models
- Allen-Bradley 1756-CNB (non-redundant ControlNet bridge)
- Allen-Bradley 1756-CN2 / CN2R modules
- Allen-Bradley 1756-EN2T Ethernet communication module
- Allen-Bradley 1756-L7x / L8x ControlLogix controllers
- Allen-Bradley 1756-IB16 / OB16E I/O modules
