AN3371 datasheet(28/45 Pages) STMICROELECTRONICS

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Overview of the STM32 advanced RTC

AN3371

28/45

Doc ID 018624 Rev 5

1.11.2

RTC_ALARM output

The RTC_ALARM output can be connected to the RTC alarm unit A or B to trigger an

external action, or routed to the RTC wakeup unit to wake up an external device.

RTC_ALARM output connected to an RTC alarm unit

When the calendar reaches the alarm A pre-programmed value in the RTC_ALRMAR

RTC_ISR register, is set to ‘1’. If the alarm A or alarm B flag is routed to the RTC_ALARM

output (RTC_CR_OSEL[1:0] =”01” for alarm A, and RTC_CR_OSEL[1:0] =”10” for alarm B),

this pin is set to VDD or to GND, depending on the polarity selected. The output toggles

when the selected alarm flag is cleared.

Figure 19. Alarm flag routed to RTC_ALARM output

RTC_ALARM output connected to the wakeup unit

When the wakeup downcounting timer reaches 0, the wakeup flag is set to ‘1’. If this flag is

selected as the source for the RTC_ALARM output (OSEL[1:0] bits set to ‘11’ in RTC_CR

long as the flag is not cleared.

MS19535V1

Alarm B

ss, mm, HH/date

Alarm A

ss, mm, HH/date

hh:mm:ss

(12/24 format)

Day/date/

month/year

Calendar

Alarm A

flag

Alarm B

flag

RTC_ALARM

output

OSEL[1:0]

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