8 AC inputs, expanded temp range — what the EOL status means for your BOM
The Siemens 6ES7321-1FF81-0AA0 is an SM 321 digital input module for the S7-300 family, carrying 8 optically isolated inputs rated for 120/230 V AC (47...63 Hz) with an expanded temperature range. The signal "1" threshold spans 79 to 264 V AC, so it reads line-voltage AC signals directly — no external signal conditioner needed between a 120 V or 230 V sensor and the backplane. This module is flagged EOL/hot in the lifecycle record — the manufacturer has ended production and the part is in the last-time-buy window or already past it. For a BOM line that still calls out this order code, the sourcing path is surplus or broker channel, quoted per RFQ against the specific quantity.
Signal thresholds and wiring constraints
Each input draws 6.5 mA typ at 120 V and 11 mA typ at 230 V. The module accepts 2-wire proximity sensors with a permissible quiescent current up to 2 mA — above that the input may not see a clean "0" signal. The "0" signal range is 0 to 40 V, so a leaky sensor that sits above 40 V in its off-state will be read as a "1". Inputs are grouped in pairs (groups of 2) with optocoupler isolation between the channels and the backplane bus. Isolation is tested at 1500 V AC. The module requires a 20-pin front connector — that connector is ordered separately and determines the wiring topology for the field cables. Maximum cable length is 1000 m shielded, 600 m unshielded. The input filter delay from "0" to "1" is 25 ms max — enough to debounce mechanical contacts but too slow for a high-speed pulse train.
Panel fit and power budget
All 8 inputs can be active simultaneously at both 40 °C and 60 °C ambient — no derating needed within the standard S7-300 enclosure limits.