Siemens 6ES5 421-8MA12 Module

Siemens 6ES5-421-8MA12 is an 8-channel digital input module for the ET 100U/ET 200U distributed I/O family, delivering 8 channels of 24 V DC inputs for sensors and switches. Each channel detects a logic 0 in the 0–5 V range and a logic 1 in the 13–33 V range, with a typical input current of 7 mA at 24 V; the eight inputs share a common L+ supply with return on M and operate without galvanic isolation between channels. The module is represented on a 10‑position terminal block (1–10), wiring includes the L+ line, and there is a red fault LED indicator that signals no input voltage. Signal timing is specified with a 2.3 ms rise time (0→1) and a 4.5 ms fall time (1→0), and unshielded cable runs can extend up to 100 m per channel. In ET100U configurations, the module is labeled 8DI, integrating into Siemens ET 200U I/O systems to expand digital input capacity and enable reliable monitoring of sensors such as pushbuttons, limit switches, and proximity sensors in industrial automation environments.