Description

Product Overview

The Allen‑Bradley 1756-CNB is a ControlNet communication scanner module built for ControlLogix PLC chassis, enabling deterministic real-time data exchange between the local controller and distributed ControlNet field devices. It plugs into the ControlLogix backplane and bridges scheduled I/O data, messaging and tag sharing across the ControlNet coaxial network, supporting up to 64 CIP connections and a maximum of 99 network nodes. This hardware resolves inconsistent or non-deterministic field communication, delivering tightly synchronized I/O updates required for continuous process and motion control applications. Automation engineers and maintenance teams rely on this module to build and sustain Allen‑Bradley ControlNet networks, with an integrated NAP RJ45 port for temporary laptop access to configure and diagnose the network without disrupting live production traffic. The module’s fixed 5 Mbps bus speed preserves data timing even under heavy network load for critical industrial control loops. Word count overview:176

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Technical Specifications

• Product Model: 1756-CNB
• Brand: Allen‑Bradley
• Warranty: One Year
• Input Voltage: Powered via ControlLogix backplane
• Operating Temperature: 0 °C to 60 °C
• Storage Temperature: -40 °C to 85 °C
• Response Time: Deterministic scheduled ControlNet update
• Protection Class: IP20 (cabinet mounted)
• Accuracy Class: Not applicable (communication module)
• Output Frequency: Not applicable
• Rated Current Range: 970 mA @5.1 V DC; 1.7 mA @24 V DC
• Communication Interface: 1 × BNC ControlNet port; 1 × NAP RJ45 service port
• Supported Protocols: ControlNet, CIP
• Overload Capacity: Backplane overcurrent protection, transient EMC protection
• Dimensions: Single slot for 1756 ControlLogix chassis
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Application Scenarios

• Continuous Chemical Process Control: This scanner module connects the ControlLogix CPU to remote ControlNet I/O racks, variable frequency drives and valve positioners. The deterministic network timing ensures synchronized analog and discrete control actions, preventing process deviation caused by variable communication latency.
• Packaging Line Motion Control: The 1756-CNB links the main controller to multiple remote ControlNet nodes on high-speed packaging machinery. Scheduled I/O transfers coordinate conveyor speeds, cut-off actions and product sensing, maintaining precise machine synchronization during continuous production runs.
• Offshore Skid Auxiliary Monitoring: Installed inside rated control enclosures, the module connects the ControlLogix rack to remote instrument clusters on oil and gas skids. Coaxial ControlNet media resists electrical interference, and the NAP port lets technicians perform diagnostics without shutting down the network.

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Key Product Notes

This single-slot ControlNet scanner works exclusively within the ControlLogix 1756 chassis and uses quad-shield RG6 coaxial cable for network wiring. It acts as a network keeper for ControlNet, managing node scheduling and media access for connected devices. Allen‑Bradley has moved this module to end-of-life status, so available spare units are used to maintain legacy ControlNet installations. Proper network tap termination and grounding are required to avoid signal reflections and communication dropouts on the coaxial bus.