AN3371 datasheet(10/45 Pages) STMICROELECTRONICS

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Overview of the STM32 advanced RTC

AN3371

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Doc ID 018624 Rev 5

1.2

RTC alarms

1.2.1

RTC alarm configuration

STM32 RTC embeds two alarms, alarm A and alarm B, which are similar. An alarm can be

generated at a given time or/and date programmed by the user.

The STM32 RTC provides a rich combination of alarms settings, and offers many features to

make it easy to configure and display these alarms settings.

Each alarm unit provides the following features:

●

Fully programmable alarm: sub-second (this is discussed later), seconds, minutes,

hours and date fields can be independently selected or masked to provide a rich

combination of alarms.

●

Ability to exit the device from low power modes when the alarm occurs.

●

The alarm event can be routed to a specific output pin with configurable polarity.

●

Dedicated alarm flags and interrupt.

Figure 6.

Alarm A fields

RTC_ALRMAR is an RTC register. The same fields are also available for the RTC_ALRMBR register.

RT_ARMASSR is an RTC register. The same field is also available for the RTC_ALRMBR register.

Maskx are bits in the RTC_ALRMAR register that enable/disable the RTC_ALARM fields used for alarm A

and calendar comparison. For more details, refer to Table 5.

Mask ss are bits in the RTC_ALRMASSR register.

An alarm consists of a register with the same length as the RTC time counter. When the

RTC time counter reaches the value programmed in the alarm register, a flag is set to

indicate that an alarm event occurred.

The STM32 RTC alarm can be configured by hardware to generate different types of

alarms. For more details, refer to Table 5.

Programming the alarm

Table 4 describes the steps required to configure alarm A.

MS19528V1

Day of week

Alarm date

12h or 24h

format

RTC_ALRMAR

Alarm time

Date

Mask2

Mask3

Mask1

Mask0

Mask ss

RTC_ALRMASSR

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