Siemens 6ES7221-1BF21-0XA0 is the EM 221 digital input module for the SIMATIC S7-200 family. It provides eight 24 V DC digital inputs that support sink or source wiring and feature optical isolation to protect the CPU from field-side transients. Intended for use with S7-22x CPUs, this module handles binary input signals from sensors and switches, enabling straightforward integration with existing S7-200 control schemes. The EM 221 extends the S7-200’s input capacity, making it suitable for compact automation projects that rely on reliable 24 V DC signal reading.
