Allen-Bradley 1771-CAD USNT Data Communications Module

Allen-Bradley 1771-CAD USNT Data Communications Module is a vintage PLC-5 era interface that functions as a data communications module within Allen-Bradley’s 1771 network family. It provides a dedicated serial communications channel for networked data exchange between a PLC-5 processor and remote I/O devices and other nodes over the Data Highway network family. The USNT designation identifies the North American region variant of the 1771-CAD family, ensuring compatibility with standard DH/DH+ network configurations used in factory automation. Intended for use inside a PLC-5 control system, the 1771-CAD supports master-level coordination of communications across multiple I/O points, enabling reliable read/write data transfers to remote modules and devices scattered across controller cabinets. Common applications include distributed control and data collection on automated lines where consistent, low-latency serial communication is required between the central controller and remote devices. This module is part of the broader 1771-C/D family offerings documented by Allen-Bradley, which describe network master behavior and compatibility within the PLC-5 ecosystem.