| 摘要 |
A plurality of key switches are provided, each of which is connected, at one end, to the ground, and at the other end, to a power supply, by means of a resistor. The key switches are coupled, at the connection point with the resistor, to input buffers. Each input buffer outputs an electrical signal when the corresponding key switch is turned on. A counter circuit is provided for counting clock signals supplied from a CPU at predetermined intervals. The output data of this counter circuit is supplied to selectors, which select one of the input buffers, in accordance with the output data of the counter circuit, and supply the output signal of the selected input buffer to the CPU.
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