Datasheet

DocID10397 Rev 20 29/44
M41T62, M41T63, M41T64, M41T65 Clock operation
3.8 Century bits
The two century bits, CB1 and CB0, are bits D7 and D6, respectively, in the century/month
register at address 06h. Together, they comprise a 2-bit counter which increments at the
turn of each century. CB1 is the most significant bit.
The user may arbitrarily assign the meaning of CB1:CB0 to represent any century value, but
the simplest way of using these bits is to extend the year register (07h) by mapping them
directly to bits 9 and 8. (The reader is reminded that the year register is in BCD format.)
Higher order year bits can be maintained in the application software.
Figure 24. Century bits CB1 and CB0
3.9 Leap year
Leap year occurs every four years, in years which are multiples of 4. For example, 2012
was a leap year. An exception to that is any year which is a multiple of 100. For example,
the year 2100 is not a leap year. A further exception is that years which are multiples of 400
are indeed leap years. Hence, while 2100 is not a leap year, 2400 is.
During any year which is a multiple of 4, the M41T6x RTC will automatically insert leap day,
February 29. Therefore, the application software must correct for this during the exception
years (2100, 2200, etc.) as noted above.
Table 9. Examples using century bits
CB1 CB0 CENTURY
0 0 2000
0 1 2100
1 0 2200
1 1 2300
00
CB1:CB0
01
1011
0000000000000000
b15 b14 b13 b12 b11 b10
b9 b8
D7 D6 D5 D4 D3 D2 D1 D0
Example: 16-bit year value
MAINTAIN
ADDITIONAL
YEAR BITS IN
SOFTWARE
LOWER 8 BITS
CONTAINED IN
YEAR REGISTER
(07h)
LET CB1:CB0 REPRESENT
BITS 9 AND 8 TO EXTEND
THE YEAR REGISTER
CB1 CB0