
RTC - 9701 JE
MQ - 362 - 03
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11.2. Description of RTC functions (addresses between 0 and 7)
The clock and the caledar consists of seconds, minutes, hours, day of the week, day, month, year and every 100 year
(SEC, MIN, HOUR, WEEK, DAY, MONTH, YEAR and Y100 registers).
Address Function bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 R/W Comments
0 SEC ¡S40 S20 S10 S8 S4 S2 S1 R/W BCD notation
1 MIN ¡M40 M20 M10 M8 M4 M2 M1 R/W BCD notation
2 HOUR ¡¡H20 H10 H8 H4 H2 H1 R/W BCD notation
3 WEEK ¡W6 W5 W4 W3 W2 W1 W0 R/W
4 DAY ¡¡D20 D10 D8 D4 D2 D1 R/W BCD notation
5 MONTH ¡¡¡C10 C8 C4 C2 C1 R/W BCD notation
6 YEAR Y80 Y40 Y20 Y10 Y8 Y4 Y2 Y1 R/W BCD notation
7 Y100 0 0 1 0 0 0 0 0 R 20 is fixed (BCD)
11.2.1. SEC register and MIN register (addresses 0 and 1)
These registers are 60-base BCD counters.
These registers are incremented at the timing when carry is generated from a lower register. At the timing when the lower
register changes from 59 to 60, carry is generated to the higher register and thus incremented. (If inappropriate value (like 65)
is set, the SEC/MIN register is cleared to “0” (at the incrementation) and carry may be generated to the higher register.)
When data is written to the MIN register, all the counters lower than it are cleared. Clearing occurs right after CLK data latch
of D0 data.
11.2.2. HOUR register (address 2)
This register is a 24-base BCD counter (24 hour format).
This register is incremented at the timing when carry is generated from the MIN register. At the timing when this register
changes from 23 to 00, carry is generated to the WEEK register and the DAY register.
24h format
a.m. 00 01 02 03 04 05 06 07 08 09 10 11
p.m. 12 13 14 15 16 17 18 19 20 21 22 23
11.2.3. WEEK register (address 3)
This register is a septenary BCD counter (counts from 0 to 6). It is incremented when carry is generated from the HOUR
register. This register does not generate carry to a higher register. Since this register is not connected with the YEAR,
MONTH and DAY registers, it needs to be set again with the matching day of the week if any of the YEAR, MONTH or DAY
registers have been changed. As in the WEEK alarm register, this register is in 2nformat.
Day of the week bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
W6 W5 W4 W3 W2 W1 W0
Sunday ¡0 0 0 0 0 0 1
Monday ¡0 0 0 0 0 1 0
Tuesday ¡0 0 0 0 1 0 0
Wednesday ¡0 0 0 1 0 0 0
Thursday ¡0 0 1 0 0 0 0
Friday ¡0 1 0 0 0 0 0
Saturday ¡1 0 0 0 0 0 0
* Be careful not to write “1” to multiple bits.
11.2.4. DAY register and MONTH register (addresses 4 and 5)
The DAY register is a variable (between 28-base and 31-base) BCD counter that is influenced by the month and the leap year.
It is incremented when carry is generated from the lower register. (If inappropriate values are set for day and month, the DAY
register is set to 01 (at incrementation) and carry may be generated to the higher register.)
DAY register: 01 to 28, 29, 30, or 31 (depending on the month and the leap year)
MONTH register: 01 to 12
Jan. Feb. Marc
h April May June July Aug. Sep. Oct. Nov. Dec.
Normal year 28Last day Leap year 31 29 31 30 31 30 31 31 30 31 30 31
11.2.5. YEAR register (address 6 and 7)
This register is a BCD counter for years 2000 to 2099. The YEAR register is extended to display the year directly. Also, the
leap year is automatically determined, which reflects in the DAY register.
Address Function bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 R/W Comments
6 YEAR Y80 Y40 Y20 Y10 Y8 Y4 Y2 Y1
R/W BCD notation
7 Y100 0 0 1 0 0 0 0 0
R 20 is fixed (BCD)
* Leap year is a year that can be divided by four (multiples of 100 is excluded except multiples of 400).