Allen-Bradley 1756-DHRIO ControlLogix DH+ Remote I/O Module

Description

Product Introduction

The Allen-Bradley 1756-DHRIO is a ControlLogix communication module designed to bridge modern ControlLogix platforms with legacy Data Highway Plus (DH+) and Remote I/O (RIO) networks. It provides two configurable communication channels, allowing ControlLogix controllers to exchange data with older PLC-5, SLC 500, PanelView, and Remote I/O systems.

In our field experience, the 1756-DHRIO is often the difference between a controlled migration and a forced shutdown. Many plants still operate validated PLC-5 or SLC systems where rewriting thousands of lines of ladder logic is not practical. This module creates a communication bridge, but engineers must remember that DH+ and RIO are legacy networks with aging cable infrastructure and configuration requirements.

Key Technical Specifications

1756-DHRIO

1756-DHRIO

Application Scenarios & The “Trench” Experience

A plant manager calls maintenance:

“The new ControlLogix rack is online, but the old PLC-5 equipment disappeared.”

The processor is fine. Ethernet is fine. The problem is the other side of the plant still speaks DH+.

This is where the 1756-DHRIO earns its place.

Legacy networks rarely fail because of one component. Cable condition, node addressing, termination, and routing paths all matter.

Typical applications include:

• Automotive Manufacturing – PLC-5 to ControlLogix migration – The 1756-DHRIO allows existing DH+ machine networks to continue operating while the control platform is upgraded.
• Packaging Systems – Legacy PanelView communication – Provides a communication path between ControlLogix systems and older operator terminals.
• Material Handling – Remote I/O replacement projects – Maintains communication with existing Remote I/O racks without immediate field rewiring.
• Water Treatment – Pump station modernization – Connects newer ControlLogix supervisory systems with older SLC controllers.
• Process Industries – Brownfield upgrades – Allows phased migration instead of full plant shutdowns.

Field Case

A production facility replaced an aging PLC-5 processor with a ControlLogix platform. The original plan was to replace every Remote I/O rack during the same outage window.

That plan changed quickly.

The wiring drawings were incomplete. Several Remote I/O drops were undocumented. The shutdown window was only 36 hours.

The engineering team installed a ControlLogix chassis with a 1756-DHRIO module and kept the existing RIO network operational. Production resumed on schedule.

The long-term migration plan continued afterward without emergency pressure.

Transparency SOP: Quality Assurance & Testing

We don’t just ship boxes; we test them on actual Allen-Bradley ControlLogix racks.

• Inbound Inspection
  • Verify Allen-Bradley label, catalog number, series, and hardware revision.
  • Inspect communication terminals, chassis connector, and module housing.
  • Check for corrosion, physical damage, or unauthorized repairs.
• Live Rack Testing
  • Install module in a ControlLogix chassis.
  • Verify module recognition through Studio 5000.
  • Test DH+ communication channel operation.
  • Test Remote I/O scanner functionality when applicable.
• Electrical Parameter Checks
  • Measure backplane current draw.
  • Verify communication port stability.
  • Confirm diagnostic LED operation.
• Firmware Verification
  • Record exact firmware revision.
  • Confirm compatibility with existing RSLogix 5000 projects.
  • Verify EDS identification files.
• Final QC & Anti-static Packaging
  • Complete communication testing.
  • Protect connectors from ESD exposure.
  • Package with anti-static materials.

The Veteran’s Tech Trap Guide

⚠️ Do not assume DH+ and RIO are interchangeable. The 1756-DHRIO supports both, but each channel must be configured correctly. A wrong channel setting can make a healthy network appear dead.

❗ Check DH+ node addressing carefully. DH+ uses octal addressing in many legacy systems. A decimal/octal mistake can send messages to the wrong controller.

⚠️ Do not ignore old cable problems. Blue Hose cable, termination resistors, grounding, and connector condition are common failure points.

⚠️ Save the routing path before replacement. Ethernet-to-DH+ gateway applications depend on correct slot, channel, and node routing information.

⚠️ Do not pull this module without following site procedures. Always verify whether your ControlLogix chassis supports energized module removal for the specific application.

Take screenshots of RSLinx routing before removing the old module. Trust me. Nobody wants to rebuild a DH+ map during a production outage.

Frequently Asked Questions (FAQ)

Q1. What is the Allen-Bradley 1756-DHRIO?

The 1756-DHRIO is a ControlLogix communication module that provides DH+ and Remote I/O connectivity for integrating legacy Allen-Bradley networks with ControlLogix systems.

Q2. What networks does the 1756-DHRIO support?

It supports:

• Data Highway Plus (DH+)
• Allen-Bradley Remote I/O (RIO)

Each communication channel can be configured according to the application requirements.

Q3. Can the 1756-DHRIO replace a communication module?

Not directly inside a rack. It is installed in a ControlLogix chassis and acts as a communication bridge to existing DH+ networks.

Q4. Can the 1756-DHRIO communicate through Ethernet?

Yes, when installed in a ControlLogix system with an EtherNet/IP communication module, it can provide routing between Ethernet networks and DH+ devices. Correct routing paths must be configured.

Q5. Is the 1756-DHRIO still manufactured?

No. Rockwell Automation discontinued the 1756-DHRIO DH Plus/RIO Communication Module on December 31, 2024. Existing systems typically rely on repair services, surplus inventory, or migration planning.

Q6. What is the difference between 1756-DHRIO and 1756-DHRIOXT?

The 1756-DHRIOXT is the extended-temperature version designed for harsher environmental conditions. Standard 1756-DHRIO is intended for normal industrial temperature ranges.

Q7. Why is a surplus 1756-DHRIO cheaper than buying directly from Rockwell?

Because the product is discontinued. Available units usually come from industrial surplus inventory, plant spare stock, and equipment retirement programs. The critical factor is documented testing, not only the label condition.

Q8. What warranty is typically provided?

Qualified automation suppliers commonly provide a 12-month warranty on tested new surplus and refurbished 1756-DHRIO modules. Always confirm warranty terms and test coverage before purchase.