UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
151 of 362
NXP Semiconductors
UM10208
Chapter 13: LPC2800 RTC
6.3 Time counter group
The time value consists of the eight counters shown in
and
.
These counters can be read or written at the locations shown in
[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.
6.3.1 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.
7.
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
Register (AMR - 0x8000 2010)” on page 149
) 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 162. 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 163. Time Counter registers
Name
Size
Description
Access
Address
SEC
6
Seconds value in the range of 0 to 59
R/W
0x8000 2020
MIN
6
Minutes value in the range of 0 to 59
R/W
0x8000 2024
HOUR
5
Hours value in the range of 0 to 23
R/W
0x8000 2028
DOM
5
Day of the 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
0x8000 202C
DOW
3
Day of the week value in the range of 0 to 6
R/W
0x8000 2030
DOY
9
Day of the year value in the range of 1 to 365 (366
for leap years)
R/W
0x8000 2034
MONTH
4
Month value in the range of 1 to 12
R/W
0x8000 2038
YEAR
12
Year value in the range of 0 to 4095
R/W
0x8000 203C