Product Overview

The Allen-Bradley 1756-DNB is a specialized communication interface card designed to link a ControlLogix® chassis to a DeviceNet™ network. Operating as a master scanner, this module facilitates the seamless integration of up to 63 downstream field devices—such as motor starters, photoelectronic sensors, and variable frequency drives—into the Logix control environment. It acts as the central hub for data arbitration, ensuring that time-critical I/O information is delivered to the processor with high deterministic reliability.

Engineered for high-capacity industrial automation, the 1756-DNB offloads the heavy lifting of network management from the CPU. It manages the complex polling sequences and heartbeat monitoring required to maintain a stable fieldbus. This module is essential for distributed control architectures where minimizing wiring costs and localized device diagnostics are top priorities.

Network Performance and Data Management

The 1756-DNB supports adjustable communication speeds, allowing for network lengths of up to 500 meters at 125 Kbps or high-speed bursts of 500 Kbps for shorter segments. To optimize bandwidth, the module utilizes multiple data triggering methods, including Cyclic, Polled, COS (Change-of-State), and Strobed messaging. This flexibility ensures that analog values are updated at a steady rate while discrete events are reported instantly upon detection.

In terms of configuration, the module interfaces directly with Rockwell Software’s RSNetWorx™ for DeviceNet. Through this environment, engineers can map I/O memory, set node addresses, and configure electronic keying to prevent incorrect device replacement. The 1756-DNB also supports "Auto-Device Replacement" (ADR), which automatically downloads configuration parameters to a new device if a failure occurs, significantly reducing Mean Time to Repair (MTTR).

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Model Number: 1756-DNB

• Module Function: DeviceNet Scanner / Communication Bridge

• Backplane Current (5.1V DC): 440 mA

• Backplane Current (24V DC): 3 mA

• DeviceNet Power Requirements: 11-25V DC (Linear bus power)

• DeviceNet Current Draw: 60 mA (at 24V DC)

• Max Number of Nodes: 64 (Scanner plus 63 devices)

• Communication Rates: 125 Kbps, 250 Kbps, 500 Kbps

• Operational Temperature: 0°C to 60°C (32°F to 140°F)

• Dimensions: 3.5 x 13.0 x 14.5 cm

• Weight: 0.9 kg

Diagnostics and Maintenance

The 1756-DNB provides an onboard four-character alphanumeric display that offers real-time status updates and error codes. This hardware-level diagnostic tool allows technicians to identify network faults, duplicate MAC IDs, or bus power issues without needing a laptop. Furthermore, the module supports bridging and routing, allowing programmers to "pass through" the ControlLogix backplane to configure field devices from a central Ethernet or ControlNet workstation.