BU9873 Datasheet, PDF (16/40 Pages) Rohm – I2C BUS Serial Interface RTC with High-precision Oscillation Adjustment

BU9873
Datasheet
3. Clock and Calendar Function
The clock and calendar function is available in this IC, ranging from seconds to years (the last two digits of a year).
Every register is configured in BCD code, and assigned to the following address respectively.
Second counter (internal address 0h)
Minute counter (internal address 1h)
Hour counter (internal address 2h)
Day-of-week counter (internal address 3h)
Day counter (internal address 4h)
Month counter (internal address 5h)
Year counter (internal address 6h)
3-1. Clock Counter (second counter, minute counter and hour counter)
Time digit in BCD code is displayed as follows.
Second counter: be reset to “00” and carried to minute digits when incremented from 59 to 00.
Minute counter: be reset to “00” and carried to hour digits when incremented from 59 to 00.
Hour counter: be reset to “00” and carried to day and day-of-the-week digits when incremented from 23 to 00 (in 24-hour
mode).
If non-existent time has been written, any carry from lower digits may cause the time counters to malfunction. Therefore,
such incorrect writing should be replaced with the writing of existent time data.
Users can choose to display time in 12-hour mode or 24-hour mode by setting the 12B/24 bit (internal address Fh).
12B/24-hour mode selection bit
12B/24
Description
0
12- hour time display system (separate for morning and afternoon)
1
24- hour time display system
Time Display Table
24-hour mode
00
01
02
03
04
05
06
07
08
09
10
11
12-hour mode
12 (AM12)
01 (AM 1)
02 (AM 2)
03 (AM 3)
04 (AM 4)
05 (AM 5)
06 (AM 6)
07 (AM 7)
08 (AM 8)
09 (AM 9)
10 (AM10)
11 (AM11)
24-hour mode
12
13
14
15
16
17
18
19
20
21
22
23
12-hour mode
32 (PM12)
21 (PM 1)
22 (PM 2)
23 (PM 3)
24 (PM 4)
25 (PM 5)
26 (PM 6)
27 (PM 7)
28 (PM 8)
29 (PM 9)
30 (PM10)
31 (PM11)
Setting the 12-hour or 24-hour mode should precede writing time data.
3-2. Day-of-week Counter
Day-of-week digits are incremented by 1 corresponding to the 7 days of week, e.g. (W4, W2, W1) = (0, 0, 0) → (0, 0, 1) → …
→ (1, 1, 0) → (0, 0, 0)
The relation between the days of week and day-of-week digits is user definable. (e.g. Sunday=0, 0, 0)
(W4, W2, W1) should not be set to (1, 1, 1).
3-3. Calendar Counter (day counter, month counter and year counter)
The automatic calendar function provides the calendar digit displayed in BCD code.
Day digits: Range from 1 to 31 (for January, March, May, July, August, October, and December)
Range from 1 to 30 (for April, June, September, and November)
Range from 1 to 29 (for February in leap years)
Range from 1 to 28 (for February in ordinary years)
Carried to month digits when reset to 1
Month digits: Range from 1 to 12 and carried to year digits when reset to 1.
Year digits: Range from 00 to 99 and 00, 04, 08… 92 and 96 are counted as leap years.
If non-existent time has been written, any carry from lower digits may cause the time counters to malfunction. Therefore,
such incorrect writing should be replaced with the writing of existent time data.
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