SIMATIC S7-1200, Digital input SM 1221, 8 DI, 24 V DC, Sink/Source SIMATIC S7-1200 Basic Controller - Flexible thanks to wide variety of communication options With signal modules you can adapt the configuration of your SIMATIC S7-1200 (except for CPU 1211C) individually to meet your requirements. For this purpose, a series of digital and analog input, output and hybrid modules is available, including fail-safe versions. Thanks to this detailed expansion option you can save space in the control cabinet and get the most from your hardware expenditure.