Samsung S5PC110 Manual page 783

S5PC110_UM 4 REAL TIME CLOCK (RTC)
4.4 READ / WRITE REGISTER
To write the BCD register in RTC block, set the Bit 0 of the RTCCON register. To display the second, minute,
hour, day of the week, day, month, and year, the CPU should read the data in BCDSEC, BCDMIN, BCDHOUR,
BCDDAYWEEK, BCDDAY, BCDMON, and BCDYEAR registers, respectively, in the RTC block. However, a one-
second deviation can exist because multiple registers are read.
For example, if you read the registers from BCDYEAR to BCDMIN, the result is assumed to be 2059 (Year), 12
(Month), 31 (Day), 23 (Hour) and 59 (Minute). If you read the BCDSEC register and the value ranges from 1 to 59
(Second), there is no problem. However, if the value is 0 sec., the year, month, day, hour, and minute can change
to 2060 (Year), 1 (Month), 1 (Day), 0 (Hour) and 0 (Minute) because of the one second deviation. In this case, you
must read again from BCDYEAR to BCDSEC if BCDSEC is zero.
4.4.1 BACKUP BATTERY OPERATION
The backup battery can drive the RTC logic. The backup battery supplies the power through the RTCVDD pin into
the RTC block, even if the system power is off. If the system is off, the interfaces of the CPU and RTC logic should
be blocked, and to minimize power dissipation the backup battery only drives the oscillation circuit and the BCD
counters.
4.5 ALARM FUNCTION
The RTC generates ALARM_INT (alarm interrupt) and ALARM_WK (alarm wake-up) at a specific time in the
power-off mode or normal operation mode. In normal operation mode, ALARM_INT is activated. In the power-off
mode, ALARM_WK signal is activated as well as the ALARM_INT. The RTC alarm register (RTCALM) determines
the alarm enable/disable status and the condition of the alarm time setting.
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