Serial data which is transmitted via a RS232 interface is converted to I² C-Bus format. The I² C-Bus is provided from a microcontroller AT89C2051 via software. So it s possible to control I² C-Bus circuits from a PC with low expense. The PC acts as the I² C-Bus master (indirectly via the microcontroller). I² C data can be both written and read, I² C acknowledge bits can be both set and evaluated.