What it is and what it does
This 6ES7321-1FH00-0AA0 is a SIMATIC S7-300 SM 321 digital input module – 16 isolated AC inputs rated for 120/230 V AC (47–63 Hz). It reads line-voltage signals from switches, proximity sensors, or pushbuttons directly, without an interposing relay. Each input group of four is optically isolated from the backplane bus.
Key ratings and what they mean for fit
20-pin front connector required (not included). Unshielded cable max. 600 m; shielded cable max. 1 000 m. Isolation tested at 4 000 V DC between channels and backplane.