The 1771-KD Interface Module is a Communication Interface Module that has been manufactured by Allen-Bradley/Rockwell Automation as part of the Allen-Bradley PLC 2 series. This module interfaces the Data Highway Module with other intelligent RS-232-C compatible devices and it can also be used as a replacement for the 1771-KC and the 1771-KE communication processor modules. Longline, direct, or modern connections can be used on this module to connect to various RS-232-C devices based on the distance from the module. The 1771-KD module can also serve as a slave interface between the SCADA master device and the Data Highway network. It has DH and RS-232-C communication ports with a baud rate of up to 19.2 kilobytes per second. The module features a maximum power supply rating of 5 Volts DC at 1.2 Amps of current and it obtains a power supply from the rack it is mounted on.

The Allen-Bradley 1771-KD Module requires one slot for installation in the 1771 I/O chassis, and it must also be mounted within 100 feet of the DH cable. For proper installation, the key band positions should be between pins 6 and 8 for the lower connector and between pins 10 and 14 for the upper connector. The 1771-KD Communication Interface Module comes with 6 switch assemblies for choosing various communication options. The 1770-CP modern interface cable, 1770-CD data highway drop-line cable, or the 1770-CG data terminal interface cable are used for wiring. This module comes with 5 LED indicators on the front for diagnosis and troubleshooting. For safety, there is a 16-bit Cycle Redundancy Check (CRC) on the DH link and a 16-bit CRC on the RS-232-C link or 8-bit Block Check Character (BCC) or a for message transmission over the Data Highway network.