8-DI module for the S7-1200 rack — what it carries and where it fits
The Siemens 6AG1221-1BF32-2XB0 is an 8-channel digital input module for the S7-1200 system, rated for 24 V DC sink inputs with a permissive range of 20.4 V to 28.8 V DC. The module draws 105 mA max from the 5 V DC backplane bus and nominally 1.5 W from the load supply. Each input group of two channels shares common isolation, so you land the return per pair. Signal thresholds are defined per the Siemens spec: a logic '1' is guaranteed at ≥15 V DC with a source current of 2.5 mA minimum, 4 mA typical; logic '0' is ≤5 V DC with a permissible quiescent current of 1 mA max. The front connector (screw or spring-cage, ordered separately) is required, and the module fits a 45 mm width on the DIN rail. The part is parameterizable, provides diagnostic alarm and status indication per channel, and includes supply voltage monitoring. For longer cable runs, unshielded cable is good to 300 m; shielded stretches to 500 m. IP20 protection keeps it inside the control cabinet.