Allen-Bradley 1785-KE Data Highway Plus Interface Module

The Allen-Bradley 1785-KE, also cataloged as the 1785-KE Data Highway Plus Interface Module, operates as a dedicated hardware component for protocol conversion and serial communication bridging within Allen-Bradley PLC-5 platforms.

Hardware Specifications

Deterministic Backplane Bus & Network Architecture

The 1785-KE resides within a standard 1771 I/O chassis, interfacing via the backplane bus to bridge asynchronous RS-232-C or RS-422-A serial protocols directly into a Data Highway Plus (DH+) deterministic network. Operating as an intelligent interface module, it offloads protocol encapsulation and buffer management from the primary PLC-5 processor, enabling programming terminals, operator interfaces, and industrial computers to execute data exchanges across the DH+ network at 57.6 kbps. Galvanic isolation on the serial interface prevents ground potential differences from interfering with backplane signal integrity.

Frequently Asked Questions

Q: What is the primary function of the 1785-KE interface module in a PLC-5 system?

A: The 1785-KE acts as a physical and protocol bridge, allowing host computers, programming devices, or HMIs with RS-232-C or RS-422-A serial ports to communicate directly with controllers on a Data Highway Plus (DH+) network.

Q: Does the 1785-KE module require external power wiring?

A: No, the 1785-KE receives its primary logic power directly from the 1771 chassis backplane bus at 5 VDC, eliminating the need for external power supply wiring to the module card.

Field Installation Guidelines

1. Power Isolation: Disconnect primary AC power from the 1771 chassis power supply before inserting or removing the 1785-KE module to protect backplane bus connectors from transient arcing.
2. Chassis Mounting: Align the module card edges with the top and bottom guides of the selected slot in the 1771 Universal I/O chassis. Slide the unit in until it seats firmly into the backplane, then lock the chassis retaining latch.
3. Serial Port Wiring: Connect serial cabling using shielded, twisted-pair conductors for RS-232-C or RS-422-A lines. Ensure cable runs do not exceed standard EIA length limits (50 feet for RS-232-C) to prevent data corruption.
4. DH+ Cable Termination: Connect DH+ twinaxial cable to the module terminal block or 9-pin connector. Install proper 82-ohm terminating resistors at both physical endpoints of the DH+ trunkline.
5. Shield Grounding: Terminate overall cable shields strictly at a single point on the main chassis ground bus to mitigate EMI noise without creating ground loops.