The R2045S/D is a real-time clock module, built in CMOS real-time clock IC and crystal oscillator, connected to the CPU by four signal lines, CE, SCLK, SI, and SO, and configured to perform serial transmission of time and calendar data to the CPU. The oscillation frequency is adjusted to high precision (05ppm: 15sec. per month at 25C) The periodic interrupt circuit is configured to generate interrupt signals with six selectable interrupts ranging from 0.5 seconds to 1 month. The 2 alarm interrupt circuits generate interrupt signals at preset times. As the oscillation circuit is driven under constant voltage, fluctuation of the oscillator frequency due to supply voltage is small, and the time keeping current is small (TYP. 0.48A at 3V). The oscillation halt sensing circuit can be used to judge the validity of internal data in such events as power-on; The supply voltage monitoring circuit is configured to record a drop in supply voltage below two selectable supply voltage monitoring threshold settings. The 32-kHz clock output function (N-channel Open drain output) is intended to output sub-clock pulses for the external microcomputer. The oscillation adjustment circuit is intended to adjust time by correcting deviations in the oscillation frequency of the crystal oscillator.