| 摘要 |
PURPOSE:To hold a present time at the time when a power source is disconnected, and also, to eliminate the need of resetting of the time at the time of turning on again by providing a time counting LSI of high accuracy which is not backed up by the power source, and a time counting LSI of low accuracy which is backed up by the power source. CONSTITUTION:An oscillator 1 is an oscillator of low accuracy whose power consumption is suppressed low, a time counting LSI 3 is operated by the oscillator 1 and counts the present time, a time counting LSI 4 is operated by an oscillator 2 of high accuracy, and a processor (PRC) 8 reads out the present time held by the LSIs 3, 4 through a processor bus 7. In such a state, when a power source is turned on to a device, the PRC 8 uses the time of the LSI 4 of high accuracy as the present time, and the LSI 3 copies the value of the LSI 4 at every prescribed time through a signal line 6. In the case the power source is disconnected, the LSI 3 is subjected to power source backup by a battery 5 and holds the present time, and when the power source is turned on in the next time, the LSI 4 copies a value of the LSI 3 and can hold the present time. |
