Allen-Bradley 1768-CNB CompactLogix Communication Module

Configured for ControlNet network integration in CompactLogix platforms, the Allen-Bradley 1768-CNB (1768-CNB Communication Interface) provides direct physical and electrical execution of high-speed data exchange across distributed I/O and controller networks.

Hardware Specifications

Backplane Bus Communication and Network Determinism

The 1768-CNB utilizes the CompactLogix backplane bus to facilitate deterministic data transfer between the controller and the ControlNet medium. The module supports I/O density scaling by allowing the connection of up to 99 nodes across the ControlNet segment. Firmware flash compatibility is managed through the ControlLogix or CompactLogix programming environment, ensuring that the communication stack remains synchronized with the master controller. The module provides a 5 Mbps communication rate, maintaining deterministic network performance for time-critical control tasks.

Frequently Asked Questions

Q: Can the 1768-CNB be installed in any slot of the CompactLogix system?

A: The 1768-CNB requires a 1768-based communication slot. It must be installed adjacent to the controller or another compatible 1768 module, following the specific physical hardware limitations of the CompactLogix 1768 chassis.

Q: Is hot-swapping supported for the 1768-CNB?

A: No. The system must be powered down before the insertion or removal of the 1768-CNB to prevent electrical damage to the backplane communication pins or internal module logic.

Field Installation Guidelines

• Module Mounting: Align the module with the 1768 backplane connector and slide it into the chassis. Ensure the locking tabs are fully engaged to provide mechanical stability and maintain the integrity of the high-speed data connection.
• Network Cabling: Use RG-6 quad-shield coaxial cable for ControlNet connections. Ensure that the cable is properly terminated with the correct impedance at both ends of the segment to prevent signal reflections and data collisions.
• Grounding: Bond the controller chassis to the cabinet's protective earth ground. Maintain a low-impedance ground path to minimize common-mode noise and ensure the 30 V isolation rating is maintained between the network and the chassis ground.
• Thermal Management: The module dissipates 17.5 BTU/hour. Ensure that the control cabinet is designed with sufficient airflow to keep the module within the 0 to 60 deg C operating temperature range, particularly when installed in densely packed racks.