SIMATIC S7-1200, digital input SM 1221, 16DI, DC 24V, sink/source SIMATIC S7-1200 Basic Controller - flexible thanks to a wide range of communication options. With signal modules, you can adapt the configuration of your SIMATIC S7-1200 (except CPU 1211C) to suit your individual requirements. A range of digital and analog input, output and mixed modules is available for this purpose, including fail-safe versions. This fine-grained design option saves you space in the control cabinet and optimizes your hardware costs.