The 3RK2200-0CU20-0AA3: Each of the four input sockets accepts a 2- or 3-wire PNP sensor; PIN 4 on each socket is the data line (D0–D3), with PIN 1 and PIN 3 carrying sensor supply L+ and L- from the AS-Interface bus. The module draws up to 270 mA total from the AS-Interface line, and the sensor supply is short-circuit and overload protected — handy when a prox gets whacked on a conveyor line.
Front addressing socket sets the slave ID; the module ships without a mounting plate, so grab one if you're wall-mounting rather than snapping onto DIN rail. Inputs switch high above 10 V, with a minimum signal-1 current of 6 mA and signal-0 leakage under 1.5 mA. Yellow LEDs on each input give a quick visual on I/O state; the green/red dual LED reports AS-Interface communication and diagnostics.