PURPOSE: To simplify an input circuit, by controlling timings of an encoder, which encodes a key input, and a serial-parallel converting circuit, which performs the parallel processing of data of this encoder, with clock pulses from a single oscillator.

CONSTITUTION: The serial input of a keyboard 1 is converted to a data signal by an encoder 2 constituted with a one-chip processor. Clocks having the 1/3 period of a quartz oscillator XL are outputted from a specific terminal T0. The output of the encoder 2 is distributed in parallel by a serial-parallel converting IC6. Data of serial-parallel conversion is transmitted to a central device through a transmission line 11. A counter IC8 which generates timing synchronizing pulses generates reference clock pulses which convert said conversion data to data of the transmission speed of 4800 or 9600 bands. Thus, data conversion is simplified with the single oscillator XL.