ISD91200 Series Technical Reference Manual
Release Date: Sep 16, 2019
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Revision 2.4
5.8
Real Time Clock (RTC)
Overview
Real Time Clock (RTC) unit provides real time clock, calendar and alarm functions. The clock source of
the RTC is an external 32.768 kHz crystal connected at pins XI32K and XO32K or from an external
32.768 kHz oscillator output fed to pin XI32K. The RTC unit provides the time (second, minute, hour) in
Time Load Register (RTC_TIME) as well as calendar (day, month, year) in Calendar Load Register
(RTC_CAL). The data is expressed in BCD (Binary Coded Decimal) format. The unit offers an alarm
function whereby the user can preset the alarm time in the Time Alarm Register (RTC_TALM) and
alarm calendar in Calendar Alarm Register (RTC_CALM).
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
RTC_TICK.TTR. When RTC counter in RTC_TIME and RTC_CAL is equal to alarm setting registers
RTC_TALM and RTC_CALM, the alarm interrupt flag (RTC_INTSTS.ALMIF) is set and the alarm
interrupt is requested if the alarm interrupt is enabled (RTC_INTEN.ALMIEN=1). The RTC Time Tick
and Alarm Match can wake the CPU from sleep mode or Standby Power-Down (SPD) mode if the
Wakeup CPU function is enabled (RTC_TICK.TWKEN=1).
5.8.1
RTC Features
Consists of a time counter (second, minute, hour) and calendar counter (day, month, year).
Alarm register (second, minute, hour, day, month, year).
12-hour or 24-hour mode is selectable.
Automatic leap year compensation.
Day of week counter.
Frequency compensate register (FCR).
All time and calendar registers are expressed in BCD code.
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.
Support RTC Time-Tick and Alarm-Match interrupt
Support CPU wakeup from sleep or standby power-down mode.
