PURPOSE: To eliminate a strobe line that starts an address decoder of the display device side, by providing a strobe signal producing circuit consisting of a circuit that detects the time point when the level is inverted and a circuit that delays the output of said detecting circuit to the side of the display device.

CONSTITUTION: Three address lines AL and four data lines DL are used to connect a CPU and a display device DSP. Then a strobe signal producing circuit consists of an OR gate G1 and a delaying circuit DLY containing a resistance R1 and a capacity C1. When no address is designated from the CPU side, three inputs A0∼A2 are set at 0 and the terminal STB of a decoder DEC of the device DSP is set at L. Then data D0∼D3 are delivered to the line DL, and a bit of the inputs A0∼A2 is set at "1" by all means when the next address is designated through the line AL. The capacity C1 is charged to set the terminal STB at H. Thus the strobe signal is obtained to the decoder DEC, and one of the outputs S1∼S7 is set at H.