Allen Bradley 1756-DHRIO Communication Module

The Allen Bradley 1756-DHRIO, also cataloged as the 1756-DHRIO Communication Module, operates as a dedicated hardware component for Data Highway Plus bridging and Remote I/O scanning within ControlLogix backplane architectures.

Configured for dual-network communication routing in ControlLogix chassis systems, the Allen Bradley 1756-DHRIO (1756-DHRIO Communication Module) provides direct physical/electrical execution of DH+ messaging and RIO scan control across two independent communication channels.

Hardware Specifications

Backplane Bus Communication Velocity and EtherNet/IP Deterministic Network Coordination (ControlLogix DH+ / RIO Layer)

The 1756-DHRIO module executes protocol translation between ControlLogix backplane scan cycles and legacy DH+ / RIO serial architectures. Channel separation maintains independent timing domains for DH+ messaging and Remote I/O scanning.

Backplane transaction throughput is constrained by scheduled task execution within ControlLogix controllers. Each channel operates with fixed baud rate selection and deterministic polling intervals defined by network configuration switches.

RIO scan logic maintains fixed rack connection mapping, supporting up to 32 RIO connections per channel with deterministic block transfer sequencing.

Frequently Asked Questions (FAQ)

Q: Can the 1756-DHRIO module be hot-swapped in an energized ControlLogix chassis?
A: Hot-swap is supported only under ControlLogix chassis rules. Network sessions are reset during module reinsertion and require reestablishment of DH+ and RIO links.

Q: What limits the maximum communication throughput on DH+ networks?
A: Throughput is constrained by selectable baud rate (57.6 / 115.2 / 230.4 Kbps) and message arbitration across shared DH+ bus access.

Q: Does each channel operate independently?
A: Yes. Each of the two channels maintains independent DH+ or RIO communication stacks with separate configuration parameters.

Field Installation Guidelines

Insert the 1756-DHRIO module into a powered-down or chassis-supported hot-insert slot according to ControlLogix mechanical alignment rails. Ensure full backplane connector engagement before applying system power.

Maintain proper separation between DH+ cabling and high-noise power conductors to reduce induced coupling on serial communication lines. Use shielded twisted pair for DH+ and ensure single-point grounding of the shield.

Verify rotary or switch-based network configuration settings prior to system startup. Incorrect baud rate selection will prevent network synchronization across DH+ or RIO segments.