| 摘要 |
A semiconductor integrated circuit, which can precisely measure the sleep time of a CPU by using a built-in oscillation circuit which does not utilize an oscillator to automatically activate the CPU, is disclosed. A communication control part of a responder mounted on a vehicle, which composes a toll road charging system, is composed of an LSI having a built-in CPU with a sleep function for automatically stopping operation clocks. The CPU is held in the sleep state for a certain time period from the time when the responder completes data communications with a ground station until the time when the responder exits the communication area of the ground station. The sleep time is measured by having a dividing counter downcount oscillation signals from a CR oscillation circuit built in the LSI. However, as the oscillation frequency of the CR oscillation circuit varies according to the operational environment, such as temperature, the CPU obtains the frequency error of the second clock pulses and correct the count value for sleep time measurement based on the reference clock pulses from a quartz oscillator, which becomes the operation clocks of its own, immediately before entering the sleep state.
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