The 1756-CN2R is a high-performance ControlNet communication bridge module manufactured by Allen‑Bradley, designed exclusively for the Allen‑Bradley ControlLogix 5570 and 5580 controller families. As a critical network interface component, it establishes reliable, deterministic ControlNet connectivity between ControlLogix backplane and the ControlNet industrial network, supporting real-time I/O control, peer-to-peer messaging, and data exchange among multiple PLC nodes on the same ControlNet trunk.

This module features dual redundant ControlNet communication ports, which is the core advantage of the 1756-CN2R variant. Redundant network ports deliver fault-tolerant network operation; if one network cable, tap or communication channel fails, the second channel automatically takes over communication without disrupting running production logic. This redundancy design makes the 1756-CN2R ideal for high-availability industrial environments where unexpected network downtime leads to heavy production losses, such as continuous process plants, power generation, oil and gas, water treatment, and automated assembly lines.

Installed directly in any available slot of a ControlLogix chassis, the 1756-CN2R communicates with the ControlLogix backplane via the high-speed backplane bus. It supports standard ControlNet communication rates at 5 Mbps, the fixed speed for ControlNet networks, and complies fully with the ControlNet specification for scheduled and unscheduled message transmission. Scheduled messages handle time-critical control data including analog and digital I/O, drive commands, and safety-related status signals, while unscheduled messages are used for programming upload/download, HMI data polling, configuration edits, and diagnostic data reading.

The 1756-CN2R supports a maximum network address range compliant with ControlNet standards, and it works seamlessly with other ControlNet devices including 1756-CNB modules, Flex I/O ControlNet adapters, PanelView HMIs, variable frequency drives, and third-party ControlNet-certified field devices. It supports network scheduling via RSNetWorx for ControlNet software. Users must configure the network schedule to allocate bandwidth for scheduled control traffic to guarantee deterministic response times across the whole network.

For physical specifications, the 1756-CN2R follows the standard ControlLogix module form factor. It operates within the industrial temperature range, tolerates vibration, electrical noise and EMI common inside factory control cabinets. The module has built-in LED status indicators for backplane communication, network A status, network B status, module health, and fault alarms. Technicians can quickly identify failures including network disconnection, duplicate node addresses, backplane communication errors, and module hardware faults directly from the front panel LEDs without dedicated diagnostic tools.

Common use cases for the Allen‑Bradley 1756-CN2R include upgrading legacy ControlNet systems, replacing end-of-life ControlNet bridge modules, building redundant ControlNet rings or trunks, connecting distributed remote I/O racks to the main ControlLogix controller, and integrating multiple ControlLogix processors for inter-controller data synchronization. Many system integrators and plant maintenance teams stock the 1756-CN2R as a spare part to minimize downtime during emergency module replacement.

When sourcing the 1756-CN2R, buyers should verify the module condition: new original sealed, surplus new open box, or tested used refurbished. Original Allen‑Bradley modules come with factory calibration, original firmware, and manufacturer warranty options. Refurbished units usually undergo full communication testing, backplane testing, and firmware reset before shipment. Always confirm firmware revision compatibility with your existing ControlLogix controller firmware version before installation, as mismatched firmware may cause communication failures or unexpected faults.

Key technical highlights of 1756-CN2R:

• Product brand: Allen‑Bradley (Rockwell Automation)
• Product number: 1756-CN2R
• Product type: ControlNet Redundant Communication Bridge Module
• Compatible series: ControlLogix
• Port configuration: Dual redundant ControlNet ports (Channel A / Channel B)
• Network speed: 5 Mbps ControlNet
• Function: Backplane to ControlNet network bridging, redundant communication
• Supported software: RSNetWorx for ControlNet, Studio 5000 Logix Designer
• Application: Process control, redundant industrial networks, real-time I/O, inter-PLC communication
• Mounting: Standard ControlLogix chassis slot installation
• Diagnostic: Multi-status LED indicators for fast troubleshooting

If you need a reliable 1756-CN2R module for your Rockwell Automation ControlLogix system, we supply genuine Allen‑Bradley industrial automation spare parts with strict quality inspection, fast worldwide shipping, professional pre-sales compatibility checking and after-sales technical support. We also provide other ControlLogix modules including digital I/O, analog modules, power supplies, controllers and other ControlNet communication adapters to complete your automation spare part list.

1756-CN2R