
REAL TIME CLOCK
S3C3410X RISC MICROPROCESSOR
16-2
LEAP YEAR GENERATOR
This block can determine whether the last date of each month is 28, 29, 30, or 31, based on data from BCDDAY,
BCDMON, and BCDYEAR. This block can also consider the leap year in deciding the last date. An 8-bit counter
can only represent 2 BCD digits, so it cannot decide whether 00 year is a leap year or not. For example, it can not
discriminate between 1900 and 2000. To solve this problem, the RTC block in S3C3410X has hard-wired logic to
support the leap year in 2000. Please note 1900 is not leap year while 2000 is leap year. Therefore, two digits of
00 in S3C3410X denote 2000, not 1900.
SAFE READ OF SEC, MIN, HOUR, DAY, MONTH, AND YEAR
It is required to set bit 0 of the RTCCON register to read and write the register in RTC block. To display the sec.,
min., hour, day, month, and year, the CPU should read the data in BCDSEC, BCDMIN, BCDHOUR, BCDDAY,
BCDDATE, BCDMON, and BCDYEAR register in RTC block. But, there may be one second deviation because of
multiple register read. For example, when user read registers from BCDYEAR to BCDMIN register, we assume
that the result was 1959(Year), 12(Month), 31(Date), 23(Hour) and 59(Minute). When user read BCDSEC
register, if the result is value from 1 to 59(Second), there is no problem. But, if the result is 0 sec., there will be
possibility for year, month, data, hour, and minute to be changed into 1960(Year), 1(Month), 1(Date), 0(Hour) and
0(Minute) because of one second deviation as above-mentioned. In this case, user should read from BCDYEAR
to BCDSEC again if BCDSEC is zero.
BACKUP BATTERY OPERATION
The RTC logic can be driven by the backup battery, which supplies the power through the RTCVDD pin into RTC
block, even if the system power is off. In this case of power-off, the interfaces of the CPU and RTC logic should
be blocked and the backup battery only drives the oscillation circuit and the BCD counters to minimize power
dissipation.
ALARM FUNCTION
The RTC can generate an alarm signal at a specified time in the power down mode or normal operation mode. In
normal operation mode, the alarm interrupt (INT_RTCA) is activated. The RTC alarm register, RTCALM, can
determine the alarm enable/disable and the condition of the alarm time setting.
RTC TIMER INTERRUPT OPERATION
The RTC generates an time interrupt at each sec/minute/hour/day in normal operation mode. In normal operation
mode, the RTC time interrupt (INT_RTCT) is activated. The RTC time interrupt control register, RINTCON,
determines the RTC time (SEC/MIN/HOUR/DAY) interrupt enable.