| 摘要 |
An input circuit of a one-chip microcomputer is connected to an external switching circuit. When an analog input signal of a significant level generated in the external switching circuit is received at an analog input terminal of the input circuit, an A/D conversion start request signal is generated in an A/D conversion start request generating circuit and is sent to an A/D converter. The operation of the A/D converter is started in response to the A/D conversion start request signal, the analog input signal received at the analog input terminal is converted into digital data, and an A/D conversion finish signal is sent from the A/D converter to a CPU of the one-chip microcomputer. The operation of the CPU is started in response to the A/D conversion finish signal, and the digital data is readout to the CPU. Therefore, the A/D converter, the CPU or a clock is not operated to wait for an analog input signal generated in the external switching circuit, but the A/D converter is operated for the A/D conversion, and the CPU is operated to read out the digital data. Accordingly, an electric power consumed in the A/D converter, the CPU and the clock can be reduced.
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