| 摘要 |
PURPOSE:To eliminate the need for a diode for preventing excess current by inserting a switch element in series with an output line of a key matrix circuit so as to select it sequentially. CONSTITUTION:A microcomputer 10 has 4-bit input/output terminals Ii, Oi and a control signal generating circuit 12 or the like and a key matrix circuit 13 is connected between input and output terminals. Moreover, a transmission gate TG is connected between a data bus 11 and the output terminals Oi and turned on/off by control signals C1-C4 of the generating circuit 12. Thus, the gates TGi are turned on sequentially according to the control signals C1-C4 and in connecting electrically row/column electrodes X, Y by depressing a key switch Ki of the key matrix circuit 13, the gate TGi is read to the microcomputer 10 via the input terminal Ii at a timing of the ON of the TGi.
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