Rainbow Electronics NUC140 - Manual (Page 42)

NUC140 Series DATA SHEET
Publication Release Date: May 31, 2010
- 42 - Revision V1.02
5.8 Real Time Clock (RTC)
5.8.1 Overview
Real Time Clock (RTC) unit provides user the real time and calendar message. The clock source of
RTC is from an external 32.768KHz crystal connected at pins X32I and X32O or from an external
32.768KHz oscillator output fed at pin X32I. The RTC unit provides the time message(second, minute,
hour) in Time Loading Register (TLR) as well as calendar message(day, month, year) in Calendar
Loading Register (CLR). The data message is expressed in BCD format. This unit offers alarm
function that user can preset the alarm time in Time Alarm Register (TAR) and alarm calendar in
Calendar Alarm Register (CAR).
The RTC unit supports periodic Time Tick and Alarm Match interrupts. The periodic interrupt has 8
period options 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, 1/2 and 1 second which are selected by
TTR(TTR[2:0]). When RTC counter in TLR and CLR is equal to alarm setting time registers TAR and
CAR, the alarm interrupt flag (RIIR.AIF) is set and the alarm interrupt is requested if the alarm interrupt
is enabled (RIER.AIER=1). The RTC Time Tick and Alarm Match can cause CPU wakeup from sleep
or power-down mode if Wakeup CPU function is enabled(TWKE(TTR[3])=1).
5.8.2 RTC Features
y There is a time counter (second, minute, hour) and calendar counter (day, month, year) for user
to check the time.
y Alarm register (second, minute, hour, day, month, year).
y 12-hour or 24-hour mode is selectable.
y Leap year compensation automatically.
y Day of week counter.
y Frequency compensate register (FCR).
y All time and calendar message is expressed in BCD code.
y Support periodic time tick interrupt with 8 period options 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, 1/2 and
1 second.
y Support RTC Time Tick and Alarm Match interrupt
y Support wake up CPU from sleep or power-down mode.