SIMATIC S7-1200, Digital Input SB 1221, 4DI, DC 24V 200kHz, M-reading. The SIMATIC S7-1200 Basic Controller is flexible due to its diverse communication options. If you only need to expand your SIMATIC S7-1200 CPU by a few inputs or outputs, signal boards are a good alternative to signal modules. Signal boards are directly plugged into the front of the controller, which is also possible with CPU 1211C, and are available as digital and analog input, output, and mixed modules. A communication board with an RS 485 interface is also available. Thus, signal boards allow for subsequent configuration expansion without requiring additional space in the control cabinet.