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10.4.2. Real-Time Clock Counter Operations
The real-time clock counter consists of second, minute, hour, AM/PM, day, month, year, and day of the
week counters and it performs counting up using the RTC1S signal. It has the following functions as well.
Recognizing leap years
The leap year recognizing algorithm used in RTCA is effective only for Christian Era years. Years
within 0 to 99 that can be divided by four without a remainder are recognized as leap years. If the
year counter = 0x00, RTCA assumes it as a common year. If a leap year is recognized, the count
range of the day counter changes when the month counter is set to February.
Corrective operation when a value out of the effective range is set
When a value out of the effective range is set to the year, day of the week, or hour (in 24H mode)
counter, the counter will be cleared to 0 at the next count-up timing. When a such value is set to the
month, day, or hour (in 12H mode) counter, the counter will be set to 1 at the next count-up timing.
30-second correction
This function is provided to set the time-of-day clock by the time signal. Writing 1 to the
RTCACTLL.RTCADJ bit adds 1 to the minute counter if the second counter represents 30 to 59
seconds, or clears the second counter with the minute counter left unchanged if the second counter
represents 0 to 29 seconds.
+1 second correction
If a second count-up timing occurred while the RTCACTLL.RTCHLD bit = 1 (count hold state), the
real-time clock counter counts up by +1 second (performs +1 second correction) after the counting
has resumed by writing 0 to the RTCACTLL.RTCHLD bit.
Note:
If two or more second count-up timings occurred while the RTCACTLL.RTCHLD bit = 1, the
counter is always corrected for +1 second only.
10.4.3. Stopwatch Control
Follow the sequences shown below to start counting of the stopwatch and to read the counter.
Count start
1. Write 1 to the RTCASWCTL.SWRST bit to reset the stopwatch counter.
2. Write 1 to the stopwatch interrupt flags in the RTCAINTF register to clear them.
3. Write 1 to the interrupt enable bits in the RTCAINTE register to enable stopwatch interrupts.
4. Write 1 to the RTCASWCTL.SWRUN bit to start stopwatch count up operation.
Counter read
1. Read the count value from the RTCASWCTL.BCD10[3:0] and BCD100[3:0] bits.
2. Read again.
i. If the two read values are the same, assume that the count values are read correctly.
ii. If different values are read, perform reading once more and compare the read value with the
previous one.
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
Seiko Epson Corporation
10-5
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