W90P710CD Datasheet, PDF (424/552 Pages) Winbond – 32-BIT ARM7TDMI-BASED MCU

W90P710CD/W90P710CDG
6.16 Real Time Clock
Real Time Clock (RTC) block can be operated by independent power supply while the system power
is off. The RTC block utilizes an external crystal to generate 32.768 KHz clock. The RTC can transmit
data to CPU as BCD values. The data include the time by second, minute, hour and the date by day,
month, and year. In addition, to reach better frequency accuracy, the RTC counter can be adjusted by
software.
RTC features are shown as below:
y Time counter (second, minute, hour) and calendar counter (day, month, year).
y Alarm register (second, minute, hour, day, month, year).
y 12/24 hour mode selectable.
y Recognize leap year automatically.
y Day of the week counter.
y Frequency compensate register (RTC_FCR).
y Beside RTC_FCR, all clock and alarm data expressed in BCD code.
y Support tick time interrupt
RTC Initiation: When RTC block is power on, programmer has to write a number (0xa5eb1357) to
RTC_INIR to reset all logic. RTC_INIR act as hardware reset circuit. Once RTC_INIR has been set as
0xa5eb1357, user cannot reload any other value.
RTC write enable: Register RTC_AER bit 15~0 is RTC read /write password. It is used to avoid
signal interference from system during system power off. RTC_AER bit 15~0 has to be set as 0xa965
before user want to write new data into all registers besides RTC_INIR. If user set RTC_AER as
0xa965, RTC_WRITE_EN will be raised high. Then user can feel free to write data into register.
RTC_WRITE_EN will keep high for a short period (about 24ms) and it will be pull low by internal state
machine automatically.
Frequency Compensation: The RTC_FCR allows software control digital compensation of a 32.768
KHz crystal oscillator. User can utilize a frequency counter to measure RTC clock in one of GPIO pin
during manufacture, and store the value in Flash memory for retrieval when the product is first power
on.
Time and Calendar counter: RTC_TLR and RTC_CLR are used to load the time and calendar.
RTC_TAR and RTC_CAR are used as alarm. They are all BCD counters.
12/24 hour Time scale selection: The 12/24 hour time scale selection depend on RTC_TSSR bit 0.
Day of the week counter: Count from Sunday to Saturday
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