8 REAL-TIME CLOCK (RTC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
8-17
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 counts 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)
0x300a08
(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 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[7:5]
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 carry 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)
0x300a09
(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.
D[7:4]
RTCYH[3:0]: RTC 10-year Counter Bits
These bits comprise a 4-bit BCD counter used to count tens of years. The counter counts from 0 to 9
with a carry over of 1 from the 1-year counter.
D[3:0]
RTCYL[3:0]: RTC 1-year Counter Bits
These bits comprise a 4-bit BCD counter used to count units of years.
The counter counts from 0 to 9 with a carry over of 1 from the month counter. This counter is reset to 0
after 9 and outputs a carry over of 1 to the 10-year counter.