| 摘要 |
PURPOSE:To prevent the signal of a key switch from passing round with a simple constitution and to prevent chattering or the like by subjecting a keyboard input to the software processing. CONSTITUTION:When a key switch 13 is turned on in optional scanning, an MPU (central processing unit) 16 discriminates whether the number of key switches depressed at present is 4 or not; and if it is 3, it is judged that passing- round does not occur, and information of the turned-on key switch 13 is registered in a key position buffer 19, and '1' is registered in a corresponding area of a status buffer 20 as a status word. When turning-on of another key switch 13 is detected again in the next scanning, the status word is rewritten with '2', and the processing corresponding to the key switch 13 is determined. If turning-on of any key switch 13 is not detected at this scanning time, this state is processed as chattering, and the status word is set to '0'.
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