Allen-Bradley 1771-A4B 16-Slot Chassis For SLC 500

The Allen-Bradley 1771-A4B is a 16-slot universal I/O chassis that serves as the backplane for 1771-series I/O modules in SLC 500 and PLC-5 style control systems. As part of the 1771 Universal I/O family, it enables flexible, mixed-module configurations—digital and analog I/O—within a single 16-slot rack, simplifying cabinet layout and wiring for expanded automation projects. The 1771-A4B accepts up to sixteen 1771 I/O modules and is designed for use in industrial environments where compact, modular expansion is needed for SLC 500 systems. Typical applications include expanding discrete I/O for manufacturing equipment, packaging lines, conveyors, and process monitoring where SLC 500 controllers manage the control loops. The chassis is identified by the A4B size designation, confirming a 16-slot backplane, with compatibility limited to 1771-series I/O modules designed for the 1771 universal I/O ecosystem. When integrating into an existing controller network, verify that your processor and I/O modules are compatible with the 1771 backplane architecture and that the rack mounting configuration aligns with your cabinet layout.