Real-Time Clock (Rtc); Introduction - ST STM32F40 Series Reference Manual

Real-time clock (RTC)

23 Real-time clock (RTC)
This section applies to the whole STM32F4xx family, unless otherwise specified.
23.1

Introduction

The real-time clock (RTC) is an independent BCD timer/counter. The RTC provides a time-
of-day clock/calendar, two programmable alarm interrupts, and a periodic programmable
wakeup flag with interrupt capability. The RTC also includes an automatic wakeup unit to
manage low power modes.
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 power-on 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).
625/1422 Doc ID 018909 Rev 4
RM0090