16 inputs at 120 VAC — the AC-input S7-300 slice
The Siemens 6ES7321-1EH01-0AA0 is a SIMATIC S7-300 SM 321 digital input module with 16 optically isolated channels, each rated for 120 VAC input at 47 to 63 Hz. The 1-signal threshold is 79 to 132 VAC, and the 0-signal threshold is 0 to 20 VAC — so a standard 120 VAC control voltage from a pushbutton or limit switch lands solidly in the ON region, while a dropped neutral or a 24 VAC pilot signal stays OFF.
Isolation groups and wiring reality
The 16 inputs are isolated from the backplane bus in groups of 4, meaning four adjacent channels share a common reference point; you cannot mix different AC phases or a separate control transformer within the same group without bridging the isolation barrier. The module uses a 20-pin front connector — the same pinout as other S7-300 SM 321 AC-input slices — so a pre-wired harness or a replacement module swaps in without re-terminating the field wiring.
End-of-life — sourcing the 6ES7321-1EH01-0AA0
No official successor order code is listed in the lifecycle data, so the replacement path is either a newer S7-300 SM 321 variant (verify the input voltage and isolation group count) or a migration to the S7-1200 / S7-1500 platform with a different form factor and wiring scheme.