Allen-Bradley 1771-IV DC Driver Logic Input PLC Module

The Allen-Bradley 1771-IV is an eight-channel DC driver logic input module designed for PLC-5 backplanes. It accepts 12–24 V DC field signals and translates them into logic-level inputs that feed the PLC-5 backplane, with wiring via the 1771-WA backplane wiring arm. This module is part of the 1771 I/O family and is intended for use in legacy automation systems that still run PLC-5 controllers. Each of the eight inputs is compatible with standard 12–24 V DC switch signals such as limit switches, pushbuttons, and other discrete sensors, enabling straightforward wiring and reliable switch-state detection. The unit interfaces directly with the PLC-5 rack backplane, drawing power and communicating through the same 1771 bus used by other 1771-series modules. Note that Rockwell Automation discontinued the Driver Logic Input Module line (including the 1771-IV) as of March 31, 2021, which can affect availability and support; customers often replace such cards with newer 1771-series or migrate to modern PLC platforms. Typical use cases include gating machine logic, safety interlocks, and process-start signals in older manufacturing lines where a compact, discrete-input module is required, while recognizing that the 1771-IV is a legacy component best matched to systems designed around PLC-5 hardware and 1771 backplane conventions.