What this module does in the rack
The 6ES7321-1CH00-0AA0 is a 16-channel digital input module for the S7-300 system, accepting both AC and DC signals from 24 V to 48 V. It reads field devices like limit switches, pushbuttons, and proximity sensors, and passes the status to the CPU via the backplane bus. Each channel is isolated from the backplane by an optocoupler, with 1500 V AC isolation tested between channels and the bus. This lets you mix field supply voltages on adjacent channels without coupling ground loops.
Signal thresholds and wiring constraints
The module recognizes a signal '0' from -5 V AC to +5 V AC, and a signal '1' from 14 V AC to 60 V AC. The input current at signal '1' is typically 2.7 mA. This wide hysteresis rejects noise on long cable runs — unshielded cable up to 600 m, shielded up to 1000 m. Input delay is fixed at 16 ms for both on-to-off and off-to-on transitions — not parameterizable. The module draws 100 mA max from the 5 V DC backplane bus. Power dissipation is 1.5 W at 24 V supply, rising to 2.8 W at 48 V. It supports 2-wire proximity sensors, with a max permissible quiescent current of 1 mA. The 40-pin front connector is required and sold separately — the module ships without one.