| 摘要 |
Noise removal and detection are performed for a signal VBUS in a detection portion in accordance with a low-frequency clock signal CLK generated by a CR oscillation circuit, and a detection signal VBD is received by a process control portion. A signal VBC detected by the detection portion is supplied to a quartz oscillation circuit as an operation-enable signal ENB. Thus, when a data transmission is designated by the signal VBUS, the quartz oscillation circuit supplies a high-frequency clock signal CK to a transmission function portion, enabling a data transmission. The operation-enable signal ENB is not supplied to the quartz oscillation circuit when data transmission is not performed. The power consumption of the CR oscillation circuit is small, so power consumption can be reduced.
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