| 摘要 |
PURPOSE:To improve the availability of an input terminal by using a scanning device which activates alternately the input keys set on the same row among those input keys arrayed into a matrix form and an input device which is connected to the input keys set on the same column as those input keys on the same row. CONSTITUTION:When a CPU 30 is started, the L signals are outputted from ports PA0 and PA1 and sent to an A/D converter 20 via an OR gate 40. Then the voltage VB of a back-up battery 25 is read out of terminals PB0-PB7 to the CPU 30 via data terminals D0-D7 of the converter 20 only when the voltage VB is lower than the reference voltage VC. Receiving the input of an input key 10, the CPU 30 performs the scan processing. In other words a row connected to the L signals received from terminals PA0-PA3 is decided together with the column of the key 10 operated by the input signals supplied from terminals PB0-PB7. Thus a single specific key is decided. Then the input terminal of the CPU 30 undergoes a key scan and also can be used as an input terminal of another electric circuit.
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