Samsung YP-P10 User Manual download pdf (Page 451)

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REAL TIME CLOCK S3C2440A RISC MICROPROCESSOR

17-2

REAL TIME CLOCK OPERATION

Clock Divider

XTOrtc

XTIrtc

Control Register

SEC MIN HOUR DAY DATE MON YEAR

Leap Year Generator

Alarm Generator

Reset Register

1 Hz

INT_RTC

RTCCON RTCALM

RTCRST

Time Tick Generator

TIME TICKTICNT

128 Hz

PMWKUP

Figure 17-1. Real Time Clock Block Diagram

LEAP YEAR GENERATOR

The Leap Year Generator can determine the last date of each month out of 28, 29, 30, or 31, based on data from

BCDDATE, BCDMON, and BCDYEAR. This block considers leap year in deciding on the last date. An 8-bit counter

can only represent 2 BCD digits, so it cannot decide whether "00" year (the year with its last two digits zeros) is a

leap year or not. For example, it cannot discriminate between 1900 and 2000. To solve this problem, the RTC block

in S3C2440A has hard-wired logic to support the leap year in 2000. Note 1900 is not leap year while 2000 is leap

year. Therefore, two digits of 00 in S3C2440A denote 2000, not 1900.

READ/WRITE REGISTERS

Bit 0 of the RTCCON register must be set high in order to write the BCD register in RTC block. To display the

second, minute, hour, date, month, and year, the CPU should read the data in BCDSEC, BCDMIN, BCDHOUR,

BCDDAY, BCDDATE, BCDMON, and BCDYEAR registers, respectively, in the RTC block. However, a one second

deviation may exist because multiple registers are read. For example, when the user reads the registers from

BCDYEAR to BCDMIN, the result is assumed to be 2059 (Year), 12 (Month), 31 (Date), 23 (Hour) and 59 (Minute).

When the user read the BCDSEC register and the value ranges from 1 to 59 (Second), there is no problem, but, if the

value is 0 sec., the year, month, date, hour, and minute may be changed to 2060 (Year), 1 (Month), 1 (Date), 0

(Hour) and 0 (Minute) because of the one second deviation that was mentioned. In this case, the user should re-read

from BCDYEAR to BCDSEC if BCDSEC is zero.

BACKUP BATTERY OPERATION

The RTC logic can be driven by the backup battery, which supplies the power through the RTCVDD pin into the RTC

block, even if the system power is off. When the system is off, the interfaces of the CPU and RTC logic should be

blocked, and the backup battery only drives the oscillation circuit and the BCD counters to minimize power

dissipation.

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