Allen-Bradley 1756-DNB ControlLogix DeviceNet Comms Module

The Allen-Bradley 1756-DNB serves as a high-performance communication link within the ControlLogix hardware platform. It primarily functions as a DeviceNet scanner to coordinate data flow between the processor and field devices. This module manages real-time information exchange for up to 63 individual network nodes. Furthermore, it bridges the gap between the controller backplane and distributed industrial components. By centralizing device management, the 1756-DNB simplifies the integration of sensors, motor starters, and actuators.

The module architecture supports seamless data routing across various network segments. Consequently, engineers can access configuration parameters and diagnostic data from a single workstation. This capability streamlines the commissioning process for large-scale automation projects. It also ensures that the central PLC maintains constant oversight of every connected field instrument.

Optimized Communication and Messaging Modes

This scanner module provides superior flexibility through multiple data transmission methods. It effectively handles Polled, Cyclic, and Change-of-State (COS) messaging to reduce network traffic. Additionally, the 1756-DNB supports bit-strobe commands for rapid synchronization of simple discrete devices. Users can configure communication speeds at 125k, 250k, or 500k baud depending on the cable distance. These selectable rates allow the system to balance speed and transmission range according to specific site needs.

The hardware design includes a front-facing four-character status display. This interface provides immediate visual feedback regarding network health and node status. Because the module supports hot-swapping, technicians can replace it without disrupting the power to the chassis. This feature minimizes unplanned downtime during maintenance or system upgrades. The robust internal circuitry also protects the backplane from electrical transients on the DeviceNet trunk line.

Comprehensive Diagnostics and Maintenance

The 1756-DNB offers deep diagnostic insights to enhance system reliability. It continuously monitors the DeviceNet network for communication errors or device failures. When an issue occurs, the module reports specific error codes to the ControlLogix processor. This detailed feedback allows maintenance teams to pinpoint faults quickly without manual inspection. Furthermore, the module integrates perfectly with Studio 5000 and RSNetWorx software for advanced configuration.

Technical Characteristics and Specifications

• Acts as a DeviceNet master to control up to 63 slave devices simultaneously.
• Supports high-speed data rates up to 500 kbps for responsive machine control.
• Provides galvanic isolation between the PLC backplane and the field network.
• Features a diagnostic display for local troubleshooting and status monitoring.
• Occupies a single slot in any standard 1756 ControlLogix chassis.
• Enables electronic keying to prevent the installation of incorrect module versions.

Technical Specifications