ST STM32L4+ Series Reference Manual page 1546

Real-time clock (RTC) applied to STM32L4Rxxx and STM32L4Sxxx only
46 Real-time clock (RTC) applied to
STM32L4Rxxx and STM32L4Sxxx only
46.1 Introduction
The RTC provides an automatic wakeup to manage all low-power modes.
The real-time clock (RTC) is an independent BCD timer/counter. The RTC provides a time-
of-day clock/calendar with programmable alarm interrupts.
The RTC includes also a periodic programmable wakeup flag with interrupt capability.
Two 32-bit registers contain the seconds, minutes, hours (12- or 24-hour format), day (day
of week), date (day of month), month, and year, expressed in binary coded decimal format
(BCD). The sub-seconds value is also available in binary format.
Compensations for 28-, 29- (leap year), 30-, and 31-day months are performed
automatically. Daylight saving time compensation can also be performed.
Additional 32-bit registers contain the programmable alarm subseconds, seconds, minutes,
hours, day, and date.
A digital calibration feature is available to compensate for any deviation in crystal oscillator
accuracy.
After Backup domain reset, all RTC registers are protected against possible parasitic write
accesses.
As long as the supply voltage remains in the operating range, the RTC never stops,
regardless of the device status (Run mode, low-power mode or under reset).
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