© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 01 — 15 August 2005
281
Philips Semiconductors
UM10139
Volume 1
Chapter 19: RTC
[1]
These values are simply incremented at the appropriate intervals and reset at the defined overflow point.
They are not calculated and must be correctly initialized in order to be meaningful.
19.4.13 Leap year calculation
The RTC does a simple bit comparison to see if the two lowest order bits of the year
counter are zero. If true, then the RTC considers that year a leap year. The RTC considers
all years evenly divisible by 4 as leap years. This algorithm is accurate from the year 1901
through the year 2099, but fails for the year 2100, which is not a leap year. The only effect
of leap year on the RTC is to alter the length of the month of February for the month, day
of month, and year counters.
19.4.14 Alarm register group
The alarm registers are shown in
. The values in these registers are compared
with the time counters. If all the unmasked (See
Section 19.4.7 “Alarm Mask Register
(AMR - 0xE002 4010)” on page 279
) alarm registers match their corresponding time
counters then an interrupt is generated. The interrupt is cleared when a one is written to
bit one of the Interrupt Location Register (ILR[1]).
Table 273: Time counter relationships and values
Counter
Size
Enabled by
Minimum value
Maximum value
Second
6
Clk1 (see
)
0
59
Minute
6
Second
0
59
Hour
5
Minute
0
23
Day of Month
5
Hour
1
28, 29, 30 or 31
Day of Week
3
Hour
0
6
Day of Year
9
Hour
1
365 or 366 (for leap year)
Month
4
Day of Month
1
12
Year
12
Month or day of Year
0
4095
Table 274: Time counter registers
Name
Size
Description
Access
Address
SEC
6
Seconds value in the range of 0 to 59
R/W
0xE002 4020
MIN
6
Minutes value in the range of 0 to 59
R/W
0xE002 4024
HOUR
5
Hours value in the range of 0 to 23
R/W
0xE002 4028
DOM
5
Day of month value in the range of 1 to 28, 29, 30,
or 31 (depending on the month and whether it is a
leap year).
R/W
0xE002 402C
DOW
3
Day of week value in the range of 0 to 6
R/W
0xE002 4030
DOY
9
Day of year value in the range of 1 to 365 (366 for
leap years)
R/W
0xE002 4034
MONTH
4
Month value in the range of 1 to 12
R/W
0xE002 4038
YEAR
12
Year value in the range of 0 to 4095
R/W
0xE002 403C