8 REAL-TIME CLOCK (RTC)
S1C17624/604/622/602/621 TECHNICAL MANUAL
Seiko Epson Corporation
8-15
Notes: • Data should not be read from or written to the counters while 1 is being carried over. (See
Section 8.3.5, “Counter Hold and Busy Flag,” and Section 8.3.7, “Counter Read.”)
• Rewriting RTC24H/RTC_CNTL0 register may corrupt the count data in this register. Therefore,
after changing the RTC24H setting, be sure to set up this register again.
D[7:6] Reserved
D[5:4] RTCDH[1:0]: RTC 10-day Counter Bits
These bits comprise a 2-bit BCD counter used to cou
nt tens of days. The counter counts from 0 to 2 or
3 with a carry over of 1 from the 1-day counter. The number of days in each month and leap years are
taken into account, so that when months change the counter is reset to 0 along with the 1-day counter,
and a carry over of 1 is output to the 1-month counter.
D[3:0] RTCDL[3:0]: RTC 1-day Counter Bits
These bits comprise a 4-bit BCD counter used to count units of days.
The counter count
s from 0 to 9 with a carry over of 1 from the hour counter. This counter is reset to 0
after 9 and outputs a carry over of 1 to the 10-day counter. The number of days in each month and leap
years are taken into account, so that the counter is reset to 1 when months change.
RTC Month Register (RTC_MONTH)
Register name Address Bit Name Function Setting Init. R/W Remarks
RTC Month
Register
(RTC_MONTH)
0x5148
(8 bits)
D7–5
–
reserved – – – 0 when being read.
D4
RTCMOH
RTC 10-month counter 0 to 1 X (*) R/W
D3–0
RTCMOL[3:0]
RTC 1-month counter 0 to 9 X (*) R/W
* Software reset (RTCRST → 1 → 0) does not affect the counter values. This register retains the value set before a software reset is
performed.
Notes: • Data should not be read from or written to the counters while 1 is being carried over. (See
Section 8.3.5, “Counter Hold and Busy F
lag,” and Section 8.3.7, “Counter Read.”)
• Rewriting RTC24H/RTC_CNTL0 register may corrupt the count data in this register. Therefore,
after changing the RTC24H setting, be sure to set up this register again.
D[7:5] Reserved
D4 RTCMOH: RTC 10-month Counter Bit
This is a tens of months count bit.
This bit is set to 1 with a carry over of 1 from the 1-month counter. When years change, this bit is reset
to 0 along with the 1-month counter, and a c
arry over of 1 is output to the 1-year counter.
D[3:0] RTCMOL[3:0]: RTC 1-month Counter Bits
These bits comprise a 4-bit BCD counter used to count units of months.
The counter counts from 0 to 9 with a carry over of 1 from the day counter. This counter is reset to 0 af-
ter 9 and outputs a carry over of 1 to the 10-month counter. The counter is reset to 1 when years change.
RTC Year Register (RTC_YEAR)
Register name Address Bit Name Function Setting Init. R/W Remarks
RTC Year
Register
(RTC_YEAR)
0x5149
(8 bits)
D7–4
RTCYH[3:0]
RTC 10-year counter 0 to 9 X (*) R/W
D3–0
RTCYL[3:0]
RTC 1-year counter 0 to 9 X (*) R/W
* Software reset (RTCRST → 1 → 0) does not affect the counter values. This register retains the value set before a software reset is
performed.
Notes: • Data should not be read from or written to the counters while 1 is being carried over. (See
Section 8.3.5, “Counter Hold and Busy Flag,” and Section 8.3.7, “Counter
Read.”)
• Rewriting RTC24H/RTC_CNTL0 register may corrupt the count data in this register. Therefore,
after changing the RTC24H setting, be sure to set up this register again.
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