Nxp Semiconductors UM10237 ユーザーズマニュアル
UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
655 of 792
NXP Semiconductors
UM10237
Chapter 26: LPC24XX Real-Time Clock (RTC) and battery RAM
6.4 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.
They are not calculated and must be correctly initialized in order to be meaningful.
6.4.1 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.
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.
Table 576. Consolidated Time register 2 (CTIME2 - address 0xE002 401C) bit description
Bit
Symbol
Description
Reset
value
value
11:0
Day of Year
Day of year value in the range of 1 to 365 (366 for leap years).
NA
31:12
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
The value read from a reserved bit is not defined.
NA
Table 577. 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 578. 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).
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)
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