Purchase now: Allen-Bradley 1756-DHRIO Bridge Module
Purchase now: Atlantechdrives provides you the 1756-DHRIO, an incredibly vital industrial communication bridge module engineered by Rockwell Automation for the ControlLogix 1756 programmable automation controller (PAC) platform. In the complex world of industrial automation, migrating an entire factory to modern EtherNet/IP networks simultaneously is often physically and financially impossible. The 1756-DHRIO serves as the ultimate transitional lifeline. It allows a state-of-the-art ControlLogix 5570 or 5580 processor to seamlessly communicate with decades-old legacy Allen-Bradley hardware, specifically classic PLC-5 systems, SLC 500 controllers, and legacy remote I/O (RIO) chassis. Equipped with two independent communication channels, this module acts as a powerful gateway, routing messages between the high-speed ControlLogix backplane and traditional Data Highway Plus (DH+) or Universal Remote I/O networks. It is the absolute cornerstone for phased plant upgrades, allowing engineers to replace aging central processors while temporarily keeping vast networks of existing field I/O intact, saving hundreds of thousands of dollars in rewiring costs.
Technical Specifications of the 1756-DHRIO
The 1756-DHRIO module provides enormous flexibility, allowing each of its two channels to be individually configured via software and hardware switches as either a DH+ network connection or a Remote I/O (RIO) Scanner/Adapter.
- Part Number: 1756-DHRIO
- Platform: ControlLogix 1756 System
- Communication Channels: 2 independent channels (Channel A and Channel B)
- Supported Protocols: Data Highway Plus (DH+) and Universal Remote I/O (RIO)
- DH+ Node Capacity: Up to 32 nodes per channel
- RIO Capacity: Supports up to 32 logical racks per channel as a Scanner
- Communication Rates: 57.6 Kbps, 115.2 Kbps, 230.4 Kbps
- Backplane Current Draw: 850 mA at 5.1V DC; 1.7 mA at 24V DC
Expert Installation Advice: The Blue Hose and Terminating Resistors
Connecting modern hardware to 1980s network technology requires strict adherence to legacy wiring rules. Expert Tip: The 1756-DHRIO utilizes the classic 3-pin Phoenix-style connector to attach to the iconic Allen-Bradley «Blue Hose» (Belden 9463 twinaxial cable). You must maintain strict polarity (Clear wire to terminal 1, Shield to terminal 2, Blue wire to terminal 3) across the entire daisy-chained network. Reversing the clear and blue wires at any single node will instantly crash the entire DH+ or RIO network. Furthermore, because these are linear bus topologies, you must install terminating resistors across the clear and blue terminals at the physical first and last devices on the wire. The resistor size (typically 82 ohms or 150 ohms) is strictly dictated by the baud rate you select. Failing to install these resistors will cause signal reflections that corrupt data packets, leading to intermittent and highly frustrating control faults.
Maintenance: Rotary Node Switches and Routing Tables
Before physically inserting the 1756-DHRIO into the chassis backplane, maintenance technicians must configure the physical rotary switches located on the side of the module’s printed circuit board. These switches dictate the DH+ node address (from 00 to 77 octal) or the RIO baud rate. If you attempt to change these switches while the module is powered up in the chassis, the changes will not take effect until the module is reset. Additionally, when using the module to route messages from modern EtherNet/IP down to DH+, engineers must carefully configure the routing tables within the RSLinx Classic software, mapping the logical ControlLogix backplane paths to the physical DH+ node addresses of the legacy PLC-5 processors.
Frequently Asked Questions (FAQs)
Q: Can the 1756-DHRIO act as an adapter on a Remote I/O network?
A: Yes. While typically used as a RIO Scanner to control older 1771 or 1746 I/O chassis, the 1756-DHRIO can also be configured as a RIO Adapter. This allows a modern ControlLogix chassis to appear as a remote I/O rack to a legacy PLC-5 scanner.
Q: Is this module compatible with ControlLogix Redundancy?
A: Yes, the 1756-DHRIO is fully supported in ControlLogix high-availability redundancy architectures, ensuring bumpless transfer of control for critical legacy networks.
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To bridge your modern ControlLogix system with legacy Data Highway Plus devices, use this module to communicate with SLC 5/04 processors.
