Allen-Bradley 1756-DHRIO Industrial Network Interface for ControlLogix Systems

Allen-Bradley 1756-DHRIO: Industrial Data Link Gateway for ControlLogix Smart Factory Networks

The Allen-Bradley 1756-DHRIO is a high-performance DH+/Remote I/O (RIO) communication gateway module designed for the ControlLogix chassis platform. In modern smart factory environments where legacy field devices must coexist with contemporary Ethernet-based supervisory systems, the 1756-DHRIO serves as the critical bridge that eliminates data isolation and enables seamless, real-time data flow across the entire automation hierarchy. From signal acquisition at the field level to data presentation at the SCADA and MES layers, this module ensures that no device is left behind in the digital transformation of your production floor.

Network Communication Table

Connected Automation Data Flow

In a typical ControlLogix-based automation architecture, the 1756-DHRIO module is installed directly into the 1756 chassis alongside the primary controller — such as the 1756-L73 or 1756-L83E ControlLogix CPU — and the 1756-EN2T EtherNet/IP communication module. This configuration allows the Logix controller to simultaneously manage modern EtherNet/IP devices and legacy DH+ or RIO networks through a single unified control platform.

On the field device side, the 1756-DHRIO connects directly to legacy SLC 500 and PLC-5 processors over the DH+ network, enabling peer-to-peer messaging, program uploads/downloads, and live data exchange without requiring hardware replacement. Remote I/O racks — including 1771 I/O chassis populated with analog input, digital output, and specialty modules — are scanned by the 1756-DHRIO acting as an RIO scanner, bringing discrete and analog signals into the ControlLogix data table in real time.

At the drive and motion layer, variable frequency drives such as the PowerFlex 700 series, when connected via DH+ adapter cards, report speed references, current feedback, and fault status directly through the 1756-DHRIO data path. This eliminates the need for separate serial converters or protocol translators at each drive cabinet, reducing wiring complexity and improving diagnostic transparency.

For HMI and operator interface integration, PanelView Plus terminals connected to the DH+ network can communicate with the ControlLogix controller through the 1756-DHRIO bridge, maintaining operator visibility into process variables, alarm states, and production counts. At the supervisory level, FactoryTalk View SE SCADA servers access real-time data from legacy DH+ nodes via the ControlLogix gateway path, enabling centralized monitoring, historian logging, and alarm management across both new and legacy network segments.

For remote diagnostics and asset management, the 1756-ENBT or 1756-EN2T module in the same chassis provides the EtherNet/IP uplink to the plant network, allowing FactoryTalk AssetCentre and RSLinx Classic to browse, monitor, and configure all DH+ and RIO nodes remotely — without requiring a technician to be physically present at the panel. This remote access capability is essential for multi-site operations and reduces mean time to repair (MTTR) significantly.

Solving Data Isolation in Industrial Sites

One of the most persistent challenges in brownfield industrial facilities is the coexistence of multiple communication protocols across different generations of equipment. A plant may have PLC-5 controllers on DH+ networks installed in the 1990s running alongside modern ControlLogix systems on EtherNet/IP — and the data from those legacy nodes is effectively invisible to the plant’s SCADA and MES systems without a proper gateway solution.

The 1756-DHRIO directly addresses this data isolation problem. By bridging DH+ and RIO networks into the ControlLogix backplane, it makes legacy device data available to the Logix controller’s data table, which is then accessible to any EtherNet/IP-connected system on the plant network. This means production counts from a 1990s-era PLC-5 line can appear on a modern FactoryTalk View SE dashboard in real time, enabling production line transparency without a full system replacement.

Protocol unification is another key benefit. Rather than maintaining separate software drivers, communication servers, and network infrastructure for DH+ and EtherNet/IP segments, the 1756-DHRIO consolidates protocol translation within the ControlLogix chassis. This simplifies network architecture, reduces the number of single points of failure, and lowers the total cost of ownership for the communication infrastructure.

For remote monitoring and predictive maintenance, the gateway enables SCADA systems to poll legacy RIO-connected sensors — including temperature transmitters, pressure transducers, and flow meters — at regular intervals, feeding data into historian databases for trend analysis and anomaly detection. When a fault condition is detected on a legacy RIO rack, the alarm propagates through the ControlLogix controller to the SCADA alarm server, triggering notifications to maintenance personnel without any manual intervention.

System expansion is equally straightforward. As production requirements grow, additional DH+ nodes or RIO racks can be added to the existing network without disrupting the ControlLogix architecture. The 1756-DHRIO supports up to 32 RIO rack addresses and multiple DH+ nodes per channel, providing substantial headroom for future expansion while protecting the existing investment in legacy field hardware.

Every 1756-DHRIO unit supplied by ZYPLC undergoes a full functional test prior to shipment, verifying DH+ channel communication, RIO scanner operation, backplane data exchange, and firmware integrity. Units are supplied with a 12-month warranty and are available from stock for fast global delivery, minimizing downtime for urgent replacement requirements.

Industrial Connectivity FAQ

Q1: What is the maximum communication distance supported by the 1756-DHRIO on a DH+ network?
The DH+ network supports cable runs of up to 3,048 meters (10,000 feet) at 57.6 Kbps using Belden 9463 shielded twisted-pair cable. At higher baud rates (115.2 or 230.4 Kbps), the maximum distance is reduced. Proper termination resistors must be installed at both ends of the DH+ trunk to ensure signal integrity and minimize communication errors.

Q2: Is the 1756-DHRIO compatible with all ControlLogix firmware versions?
The 1756-DHRIO is compatible with a wide range of ControlLogix controller firmware versions. However, Rockwell Automation recommends verifying compatibility between the module firmware revision and the Logix controller firmware using the Product Compatibility and Download Center (PCDC). ZYPLC supplies modules with tested firmware and can advise on compatibility for your specific controller revision upon request.

Q3: Can the 1756-DHRIO be used to connect a ControlLogix system to a legacy PLC-5 or SLC 500 for data exchange?
Yes. The 1756-DHRIO enables MSG (message) instructions in the ControlLogix controller to communicate directly with PLC-5 and SLC 500 processors on the DH+ network. This supports read/write operations on data files, program uploads/downloads, and peer-to-peer data exchange — making it the standard solution for ControlLogix-to-legacy PLC integration without replacing the existing controllers.

Q4: What warranty and testing does ZYPLC provide with the 1756-DHRIO?
All 1756-DHRIO modules supplied by ZYPLC are fully tested and inspected before shipment, covering DH+ channel A and B communication, RIO scanner functionality, backplane interface integrity, and LED status verification. Each unit is backed by a 12-month warranty against manufacturing defects and functional failures. Our technical team provides pre-sale compatibility consultation and post-sale support to ensure successful integration into your automation system.

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