Allen-Bradley 1756-DHRIO ControlLogix DH+ and Remote I/O Module
A chassis communication module for legacy Data Highway Plus messaging and Remote I/O scanner operation.
Overview
1756-DHRIO is an Allen-Bradley ControlLogix communication module that bridges a Logix chassis to Data Highway Plus or Universal Remote I/O networks. Channel A and Channel B can be assigned to the legacy network duties required by the installed architecture.
The module supports DH+ message routing and Remote I/O scanning for digital and block-transfer data. A controlled replacement must preserve the module series, firmware, channel configuration and any stored routing table.
Specs
| Manufacturer | Rockwell Automation / Allen-Bradley |
|---|---|
| Catalog Number | 1756-DHRIO |
| Platform | ControlLogix Bulletin 1756 |
| Network Function | Data Highway Plus and Universal Remote I/O |
| Network Channels | 2, individually selectable for DH+ or Remote I/O |
| Communication Rates | 57.6, 115.2 or 230.4 Kbps |
| DH+ Capacity | 32 DH+ messages per module |
| Remote I/O Role | Scanner only |
| RIO Capacity per Channel | 32 logical rack connections |
| Block Transfers per RIO Channel | 16 connections |
| Current Draw at 5.1 V DC | 850 mA |
| Current Draw at 24 V DC | 1.7 mA |
| Power Dissipation | 4.5 W |
| Module Width | 1 ControlLogix slot |
| Operating Temperature | 0 to 60 °C |
Features
- DH+ messaging allows ControlLogix applications to exchange data with established PLC-5, SLC and operator-interface assets.
- Remote I/O scanner operation transfers discrete and block-transfer data to compatible legacy adapters.
- The front programming connector is electrically associated with Channel A, which must be considered when planning service access.
- Status indicators expose module and channel conditions during commissioning and network troubleshooting.
Applications
- ControlLogix integration with brownfield DH+ messaging networks.
- Scanner service for installed Remote I/O racks and intelligent adapters.
- Phased modernization projects that retain legacy field networks while controller architecture is updated.
Lifecycle
- Rockwell Automation lists the product as discontinued from 31 December 2024 and classifies the replacement path as an engineering replacement.
- Archive the Logix project, channel selections, node addresses and routing table before module removal.
- When a Series E unit replaces an earlier series, use compatible Series E firmware and restore the routing information required by the application.
- Validate messages, rack ownership, block transfers, operator interfaces and fault recovery under controlled plant conditions.
FAQ
Can a current-series 1756-DHRIO replace an earlier module series?
A Series E module can serve in an earlier installation, but firmware compatibility and the saved routing table must be handled as part of the change.
Can 1756-RIO be used as a direct substitute for 1756-DHRIO?
Not when DH+ messaging is required. The 1756-RIO has different Remote I/O capabilities and does not provide the same DH+ function.
What configuration should be backed up before changing 1756-DHRIO?
Retain the complete Logix project, channel modes, baud rates, node addresses, rack definitions, block transfers and message-routing data.
What cabling information matters when ordering 1756-DHRIO?
Identify the installed Belden twinaxial cable, connector condition, selected data rate, network length, termination and grounding arrangement.
How should 1756-DHRIO be commissioned after replacement?
Confirm chassis recognition first, then validate each channel separately before proving all messages, rack data and machine interlocks.
What should be included in a quotation request for 1756-DHRIO?
Provide the full catalog label, hardware series, firmware revision, channel duties, chassis type, project version and required test documentation.
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