The Allen-Bradley 1771-ASB Remote I/O Adapter is the interface module that links a PLC-5 processor to remote I/O racks on the 1771 Remote I/O network. It installs in a Universal I/O chassis (1771-A1B, 1771-A2B, 1771-A3B, or 1771-A4B) and communicates with the PLC-5 controller over a half‑duplex remote I/O link at 57.6K, 115.2K, or 230.4K baud. This module is part of the PLC‑5 1771 I/O family and enables remote I/O scanning across connected racks. Rockwell Automation discontinued the 1771 Remote I/O Adapter Module as of December 31, 2017, so new availability is limited to used or refurbished units.
