S7-1200 SM1221 Digital Inputs

SM1221 digital input modules are the practical extension path when an S7-1200 CPU still fits the control job but the field signal count has grown. The family matters most in retrofit and expansion work where it is cheaper and cleaner to extend the installed controller than to reopen the architecture discussion. Use this series page to compare channel count and signal expectations while keeping slot use and wiring implications in view. The right order code is the one that fits the real signal map, not just the cabinet bill of material. S7-1200 SM1221 Digital Inputs currently indexes 2 model entries in this seed. Use that list as a decision queue, not as proof that every order code is equivalent for your application.