The I² C-I/O-Expander is an example for easily providing input and output ports for the I² C bus. The I² C circuit PCF8574 provides 8 bidirectional port pins. A LED (LD1-LD8) is connected to each port pin, which is activated with a LOW signal at the corresponding port pin. Furthermore a DIP switch (S1-1 - S1-8) is connected to each ort pin. At opened switch, the PCF8574 reads a HIGH signal, at closed switch it reads a LOW signal, but therefore it is necessary to set the corresponding port pins of the PCF8574 to a HIGH signal via I² C bus. The position of the switch is also shown via a LED, it is activated at closed switch.