Alarm Output; Rtc And Low-Power Modes; Rtc Interrupts; Table 78. Effect Of Low-Power Modes On Rtc - ST STM32F205 series Reference Manual

RM0033
22.3.13

Alarm output

Three functions can be selected on Alarm output: ALRAF, ALRBF and WUTF. These
functions reflect the contents of the corresponding flags in the RTC_ISR register.
The OSEL[1:0] control bits in the RTC_CR register are used to activate the alarm alternate
function output (AFO_ALARM) in RTC_AF1, and to select the function which is output on
AFO_ALARM.
The polarity of the output is determined by the POL control bit in RTC_CR so that the
opposite of the selected flag bit is output when POL is set to 1.
Alarm alternate function output
AFO_ALARM can be configured in output open drain or output push-pull using the control
bit ALARMOUTTYPE in the RTC_TAFCR register.
Note: Once AFO_ALARM is enabled, it has priority over AFO_CALIB (COE bit is don't care on
RTC_AF1).
When RTC_CALIB or RTC_ALARM is selected, RTC_AF1 is automatically configured in
output alternate function.
22.4

RTC and low-power modes

Mode
Sleep
Stop
Standby
22.5

RTC interrupts

All RTC interrupts are connected to the EXTI controller.
To enable the RTC Alarm interrupt, the following sequence is required:
1. Configure and enable the EXTI Line 17 in interrupt mode and select the rising edge
sensitivity.
2. Configure and enable the RTC_Alarm IRQ channel in the NVIC.
3. Configure the RTC to generate RTC alarms (Alarm A or Alarm B).
To enable the RTC Wakeup interrupt, the following sequence is required:
1. Configure and enable the EXTI Line 22 in interrupt mode and select the rising edge
sensitivity.
2. Configure and enable the RTC_WKUP IRQ channel in the NVIC.
3. Configure the RTC to generate the RTC wakeup timer event.

Table 78. Effect of low-power modes on RTC

No effect
RTC interrupts cause the device to exit the Sleep mode.
The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
tamper event, RTC time stamp event, and RTC Wakeup cause the device to exit the Stop
mode.
The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
tamper event, RTC time stamp event, and RTC Wakeup cause the device to exit the
Standby mode.
Description
RM0033 Rev 8
Real-time clock (RTC)
581/1378
597