1756-DHRIO | Allen-Bradley ControlLogix DH+/RIO Bridge Module

Introduction to the 1756-DHRIO

When a production line relies on both Data Highway Plus (DH+) and Remote I/O (RIO) networks, the 1756-DHRIO from Allen-Bradley provides a reliable bridge. This ControlLogix communication module supports two channels, each with a 3-pin terminal for wiring DH+ or RIO, plus a single 8-pin mini-DIN port connected in parallel to Channel A. Designed for the 1756 ControlLogix chassis, it enables information exchange among PLCs, SLCs, and ControlLogix controllers, even across different networks.

Key Features and Technical Specifications

• Two communication channels (Channel A and Channel B) with 3-pin terminals for DH+ or RIO wiring.
• Supports communication speeds of 57.6 Kbaud, 115.2 Kbaud, and 230.4 Kbaud, depending on cable length.
• Backplane current draw: 1.7 milliamps at 5 Volts and 850 milliamps at 24 Volts.
• Maximum power dissipation of 4.5 Watts and thermal dissipation of 15.4 BTU per hour.
• Operating temperature range: 0 to 60 degrees Celsius (32 to 140 degrees Fahrenheit).
• Weight: 0.64 pounds (0.293 kilograms).
• Slot width: 1.
• Recommended cable: Belden 89463 twinaxial, 0.52 mm² (20 AWG), rated at 200 °C (392 °F).

The 1756-DHRIO supports Remote I/O, Control and Information Protocol (CIP) Messaging, and DH+ Messaging. It can handle up to 32 Logix connections and can act as an adapter or scanner on a remote I/O network, transferring analog, digital, block, and specialty data even without message instructions.

Real-World Applications

In a typical automotive assembly plant, the 1756-DHRIO connects legacy DH+ devices to modern ControlLogix controllers, ensuring smooth data flow. It also supports Flex IO and POINT IO systems, making it versatile for various industrial setups. The module can transfer messages through a maximum of three chassis and four communication networks, which is ideal for distributed control architectures.

Installation and Setup

Before installing the 1756-DHRIO, program the network type switches for each channel and install a ControlLogix power supply and chassis. You can install multiple modules in the same chassis, but ensure your power supply can handle the load. Modules can be installed or removed with power applied, but always observe safety precautions—ensure the area is nonhazardous and power is removed to prevent electrical arcs. Also, discharge static electricity because the module is sensitive to electrostatic discharge.

Maintenance and Reliability

For long-term reliability, periodically inspect the module's connections and ensure the recommended Belden 89463 twinaxial cable is used. The cable is rated at 200 °C (392 °F), making it suitable for high-temperature environments. Check that terminating resistors are correctly installed at the first and last nodes of the network, as per the daisy-chain topology. For 230.4 Kbaud, use 82 Ohms; for 57.6 or 115.2 Kbaud, use 150 Ohms. These resistors are placed across line 1 and line 2 of the cable, with the shield as the third conductor.

Compatibility and Integration

The 1756-DHRIO integrates seamlessly with ControlLogix controllers and supports communication with Flex IO, POINT IO, PLC-5, SLC, and CompactLogix systems. It uses the same cable type for both RIO and DH+ protocols, simplifying wiring. The spare connector kit is Phoenix MVSTBR2.5/3-ST BK AU, ensuring easy replacement.

Troubleshooting Common Issues

If communication issues arise, first verify the network type switches are set correctly for each channel. Check that terminating resistors match the network speed—82 Ohms for 230.4 Kbaud, 150 Ohms for 57.6 or 115.2 Kbaud. Ensure the cable is properly terminated: for RIO, connect line 1 to terminal 1, shield to middle, and line 2 to the last pin; for DH+, reverse line 1 and line 2. Also, confirm that the module is seated firmly in the chassis and that the backplane current draw is within the power supply's capacity.

FAQ

Q: What communication speeds does the 1756-DHRIO support?

A: The 1756-DHRIO supports 57.6 Kbaud, 115.2 Kbaud, and 230.4 Kbaud, depending on cable length.

Q: Can the 1756-DHRIO act as both adapter and scanner?

A: Yes, when connected to a remote I/O network, it can operate as an adapter or scanner.

Q: What is the recommended cable for the 1756-DHRIO?

A: Use Belden 89463 twinaxial cable, 0.52 mm² (20 AWG), rated at 200 °C (392 °F).

Q: How many Logix connections can the 1756-DHRIO support?

A: It supports up to 32 Logix connections.

Q: What is the power dissipation of the 1756-DHRIO?

A: Maximum power dissipation is 4.5 Watts.

Product Support and Availability

The 1756-DHRIO is available from Petro Auto Tech. Contact us for current availability and lifecycle status. We are your trusted industrial automation parts supplier.