Allen-Bradley 1756-CN2 ControlLogix ControlNet Bridge Module

Product Overview

The Allen-Bradley 1756-CN2 is a high-performance ControlNet bridge module designed for the rugged ControlLogix automation environment. Acting as a deterministic communications interface, this module establishes high-speed, real-time links between ControlLogix controllers and distributed I/O racks, variable frequency drives, or other intelligent field platforms. Weighing a compact 0.26 kg (0.57 lbs), the single-slot 1756-CN2 routes scheduled and unscheduled peer-to-peer data over a reliable 5 Mbps ControlNet network line, ensuring deterministic timing that is completely unaffected by changes in node configuration or general network traffic overhead.

Core Technical Advantages

• High-Capacity Network Bridging: Manages up to 131 total connections (including 100 dedicated Logix communication paths and separate unscheduled channels) to efficiently facilitate dense, factory-wide controller message routing.
• Deterministic High-Speed Backplane: Utilizes a fixed 5 Mbps ControlNet communication rate to ensure time-critical interlocking data arrives precisely when expected, avoiding the jitter or packet collisions common in non-deterministic architectures.
• Rugged Environmental Engineering: Rated for operational shock conditions up to 30G and 2.0G of continuous mechanical vibration, this module delivers robust hardware endurance across an industrial temperature envelope of 0 to 60 degrees Celsius.

Technical Specifications

Installation & Engineering Guide

• Chassis Slot Installation: Isolate power to the local ControlLogix rack housing before mounting. Align the 0.26 kg communication hardware card inside the physical guide rails of any open slot, pushing straight back until the dual locking clips snap securely onto the structural frame.
• Coaxial Tap Connectivity: Wire the ControlNet network link using standard RG-6 coaxial cables and approved ControlNet taps. Ensure that the active node switches on the front panel or configuration software are addressed uniquely before applying power to prevent network communication faults.
• Network Update Interval (NUT) Tuning: Use RSNetWorx for ControlNet to properly schedule network data traffic. The 1756-CN2 allows you to prioritize time-sensitive interlocking signals via the scheduled data band while routing broad diagnostic diagnostic data via unscheduled slots.

Technical FAQs

Q1: What does "deterministic communication" mean when utilizing the 1756-CN2 on ControlNet?
A1: Deterministic communication means that the transmission time for your critical system data is mathematically guaranteed. Unlike standard Ethernet networks where packet collisions can cause unexpected execution delays, the 5 Mbps ControlNet frame provides a predictable schedule so that I/O states updates are delivered reliably cycle after cycle.

Q2: How does the 1756-CN2 module balance scheduled versus unscheduled traffic?
A2: The module manages a total budget of 131 connections. It reserves 100 solid paths for scheduled Logix controller updates (like safety lines or remote I/O loops), leaving the remaining buffer slots available for unscheduled actions like loading programs, checking web pages, or pulling non-critical hardware diagnostics.

Q3: Does the low 0.26 kg weight profile mean the hardware is prone to damage in heavy manufacturing settings?
A3: No. The efficient 0.26 kg structural weight is the result of a compact, single-slot integration strategy. The internal electronics are fully engineered to withstand up to 30G of operational shock forces and 2.0G of industrial vibration without losing backplane connectivity.