Real-Time Clock (Rtc); Introduction; Rtc Main Features - STMicroelectronics STM32F05 series Reference Manual

RM0091
24

Real-time clock (RTC)

24.1

Introduction

The real-time clock (RTC) is an independent BCD timer/counter. The RTC provides a time-
of-day clock/calendar with programmable alarm interrupt.
The RTC provides an automatic wakeup to manage all 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).
24.2

RTC main features

The RTC unit main features are the following (see
●
Calendar with subseconds, seconds, minutes, hours (12 or 24 format), day (day of
week), date (day of month), month, and year.
●
Daylight saving compensation programmable by software.
●
Programmable alarm with interrupt function. The alarm can be triggered by any
combination of the calendar fields.
●
Reference clock detection: a more precise second source clock (50 or 60 Hz) can be
used to enhance the calendar precision.
●
Accurate synchronization with an external clock using the subsecond shift feature.
●
Digital calibration circuit (periodic counter correction): 0.95 ppm accuracy, obtained in a
calibration window of several seconds
● Time-stamp function for event saving
●
Tamper detection event with configurable filter and internal pull-up
●
Maskable interrupts/events:
–
–
–
●
Backup registers: the backup registers are reset when a tamper detection event occurs.
Alarm A
Time-stamp
Tamper detection
Doc ID 018940 Rev 1
Real-time clock (RTC)
Figure 227: RTC block diagram):
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