Allen-Bradley 1768-CNBR ControlNet Bridge Module

The Allen-Bradley 1768-CNBR, also cataloged as the 1768-CNBR ControlNet Bridge Module, operates as a dedicated hardware component for deterministic network communication within CompactLogix control platforms. This module executes data transfer across ControlNet media, providing synchronized connectivity for distributed I/O and controller-to-controller messaging.

Hardware Specifications

Profinet / EtherNet/IP Deterministic Networks

The 1768-CNBR utilizes ControlNet's time-division multiple access (TDMA) scheduling to ensure deterministic data delivery across the network fabric. The module manages up to 48 Logix connections, maintaining strict timing cycles necessary for high-speed I/O updates. Communication integrity is sustained via quad-shield RG6 coaxial cabling, which minimizes electromagnetic interference. The module supports a maximum of 99 nodes, requiring precise configuration of network update times (NUT) to prevent packet collisions and ensure synchronized execution across the backplane bus. Firmware integration must be verified against the host CompactLogix controller to maintain full communication bandwidth and protocol compatibility.

Frequently Asked Questions

Q: Can the 1768-CNBR be installed or removed while the CompactLogix system is powered?

A: No. The 1768-CNBR does not support hot-swapping. Inserting or removing the module while the chassis is powered can result in electrical arcing at the backplane pins and permanent damage to the module communication circuits.

Q: What is the impact of reaching the 48-connection limit on network performance?

A: Exceeding the 48 Logix connection limit will result in the inability to establish further communication paths, leading to potential controller faults. Users must audit the connection count during system design to ensure sufficient bandwidth for all scheduled and unscheduled messaging.

Field Installation Guidelines

• Cable Management: Use only qualified RG6 quad-shield coaxial cable for BNC connections. Ensure the cable bend radius is maintained at least 10 times the cable diameter to prevent mechanical stress on the shielding.
• Grounding: Ensure the ControlNet trunk is grounded at only one point to prevent ground loops. Shielding must be terminated according to the standard ControlNet installation guidelines to mitigate noise in high-vibration environments.
• Environment: Install the module in an enclosure rated for the local environment. While the operating temperature range is 0 deg C to 60 deg C, maintain clear air gaps around the module to facilitate passive thermal dissipation.
• Termination: Ensure all unused BNC ports on the ControlNet network are terminated with a 75 ohm resistor to prevent signal reflections that compromise deterministic performance.