Real Time Clock 251 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2194/2292/2294ARM-based Microcontroller
TIME COUNTER GROUP
The time value consists of the eight counters shown in Tables 186 and 187. These counters can be read or written at the locations
shown in Table 187.
Notes:
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.
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.
Table 186: Time Counter Relationships and Values
Counter Size Enabled by Min value Maximum value
Second 6 Clk1 (see Figure 44) 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 187: Time Counter registers
Address Name Size Description Access
0xE0024020 SEC 6 Seconds value in the range of 0 to 59. R/W
0xE0024024 MIN 6 Minutes value in the range of 0 to 59. R/W
0xE0024028 HOUR 5 Hours value in the range of 0 to 23. R/W
0xE002402C 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).
1
R/W
0xE0024030 DOW 3 Day of week value in the range of 0 to 6.
1
R/W
0xE0024034 DOY 9 Day of year value in the range of 1 to 365 (366 for leap years).
1
R/W
0xE0024038 MONTH 4 Month value in the range of 1 to 12. R/W
0xE002403C YEAR 12 Year value in the range of 0 to 4095. R/W
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