6ES7321-1EH01-0AA0 is a SIMATIC S7-300 digital input module (SM 321) featuring 16 optically isolated inputs for 120 V AC signals. It connects to the S7-300 backplane via a 1 × 20-pole interface, delivering galvanic isolation between field wiring and the controller to improve noise immunity in industrial environments. This module is used to read the state of 120 V AC sensors and switches, expanding the controller's I/O while maintaining safety and signal integrity.
