SIMATIC S7-1200, digital input SB 1221, 4DI, DC 24V 200kHz, M-reading SIMATIC S7-1200 Basic Controller - flexible thanks to a wide range of 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 plugged directly into the front of the controller (also possible with CPU 1211C) and are available as digital and analog input, output and mixed modules. A communication board with RS 485 interface is also available. Signal boards also enable the configuration to be expanded later without requiring additional space in the control cabinet.