8 REAL-TIME CLOCK (RTC)
8-16
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
RTC Hour Register (RTC_HOUR)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
RTC Hour
Register
(RTC_HOUR)
0x300a06
(8 bits)
D7
–
reserved
–
–
–
0 when being read.
D6
RTCAP
AM/PM indicator
1 PM
0 AM
X (
*
) R/W
D5–4 RTCHH[1:0] RTC 10-hour counter
0 to 2 or 0 to 1
X (
*
) R/W
D3–0 RTCHL[3:0] RTC 1-hour 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.
D7
Reserved
D6
RTCAP: AM/PM Indicator Bit
When 12-hour mode is selected, this bit indicates A.M. or P.M.
1 (R/W): P.M.
0 (R/W): A.M.
This bit is only effective when RTC24H/RTC_CNTL0 register is set to 0 (12-hour mode).
When 24-hour mode is selected, this bit is fixed to 0. In this case, do not write 1 to RTCAP.
Note: The RTCAP bit keeps the current set value even if RTC24H/RTC_CNTL0 register is changed
from 12-hour mode to 24-hour mode, and will be fixed at 0 after the hour counter is updated (or
reset in software).
D[5:4]
RTCHH[1:0]: RTC 10-hour Counter Bits
These bits comprise a 2-bit BCD counter used to count tens of hours.
With a carry over of 1 from the 1-hour counter, the counter counts from 0 to 1 when 12-hour mode is
selected, or from 0 to 2 when 24-hour mode is selected. The counter is reset at 12 o’clock or 24 o’clock,
and outputs a carry over of 1 to the 1-day counter.
D[3:0]
RTCHL[3:0]: RTC 1-hour Counter Bits
These bits comprise a 4-bit BCD counter used to count units of hours.
The counter counts from 0 to 9 with a carry over of 1 from the 10-minute counter. This counter is reset
to 0 after 9 and outputs a carry over of 1 to the 10-hour counter. Depending on whether 12-hour mode
or 24-hour mode is selected, the counter is reset at 12 o’clock or 24 o’clock.
RTC Day Register (RTC_DAY)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
RTC Day
Register
(RTC_DAY)
0x300a07
(8 bits)
D7–6 –
reserved
–
–
–
0 when being read.
D5–4 RTCDH[1:0] RTC 10-day counter
0 to 3
X (
*
) R/W
D3–0 RTCDL[3:0] RTC 1-day 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[7:6]
Reserved
D[5:4]
RTCDH[1:0]: RTC 10-day Counter Bits
These bits comprise a 2-bit BCD counter used to count 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.