Allen-Bradley 1771-ASB Remote Input Output Adapter Module

Allen-Bradley 1771-ASB Remote I/O Adapter Module is the remote I/O interface used in PLC-5 systems to connect a control processor with distant I/O racks. It resides in a Universal I/O chassis and serves as the interface between the controller and the PLC-2/3/5 remote I/O network. The ASB translates the processor’s I/O requests into data transfers for remote I/O modules and returns input data to the controller, enabling coordinated control across a dispersed plant floor. Each I/O group within the adaptor provides 16 input bits and 16 output bits, supporting 32-point addressing per group, with multiple groups in a single module for larger remote configurations. The 1771-ASB family can mix with 1771-ASB/B and 1771-AS in the same remote system, subject to timing constraints and baud-rate compatibility, typically 57.6 kbit/s or 115.2 kbit/s. In operation, the adapter handles parallel read/write of both input and output modules, aligning the PLC-5 data words to the remote rack’s I/O words and preserving synchronized I/O scanning across the network. This module is part of the 1771 Remote I/O ecosystem, offering a compact, installable solution for expanding control and data acquisition points in legacy PLC-5, PLC-2, and related architectures.