3. PI8 can be used as the RTC_AF2 pin
39.2.2 Backup Domain Reset
The backup domain reset sets all RTC registers and the RCC_BDCR register to their reset
values. The BKPSRAM is not affected by this reset. The only way to reset the BKPSRAM is
through the Flash interface by requesting a protection level change from 1 to 0.
A backup domain reset is generated when one of the following events occurs:
1. Software reset, triggered by setting the BDRST bit in the RCC Backup domain control
register (RCC_BDCR).
2. VDD or VBAT power on, if both supplies have previously been powered off.
39.2.3 Backup Domain Access
After reset, the backup domain (RTC registers, RTC backup data registers and backup
SRAM) is protected against possible unwanted write accesses.
To enable access to the RTC Domain and RTC registers, proceed as follows:
Enable the Power Controller (PWR) APB1 interface clock using the
__HAL_RCC_PWR_CLK_ENABLE() function.
Enable access to RTC domain using the HAL_PWR_EnableBkUpAccess() function.
Select the RTC clock source using the __HAL_RCC_RTC_CONFIG() function.
Enable RTC Clock using the __HAL_RCC_RTC_ENABLE() function.
39.2.4 How to use this driver
Enable the RTC domain access (see description in the section above).
Configure the RTC Prescaler (Asynchronous and Synchronous) and RTC hour format
using the HAL_RTC_Init() function.
Time and Date configuration
To configure the RTC Calendar (Time and Date) use the HAL_RTC_SetTime() and
HAL_RTC_SetDate() functions.
To read the RTC Calendar, use the HAL_RTC_GetTime() and HAL_RTC_GetDate()
functions.
Alarm configuration
To configure the RTC Alarm use the HAL_RTC_SetAlarm() function. You can also
configure the RTC Alarm with interrupt mode using the HAL_RTC_SetAlarm_IT()
function.
To read the RTC Alarm, use the HAL_RTC_GetAlarm() function.
39.2.5 RTC and low power modes
The MCU can be woken up from a low power mode by an RTC alternate function.
The RTC alternate functions are the RTC alarms (Alarm A and Alarm B), RTC wake-up,
RTC tamper event detection and RTC time stamp event detection. These RTC alternate
functions can wake up the system from the Stop and Standby low power modes.
The system can also wake up from low power modes without depending on an external
interrupt (Auto-wake-up mode), by using the RTC alarm or the RTC wake-up events.
The RTC provides a programmable time base for waking up from the Stop or Standby
mode at regular intervals. Wake-up from STOP and STANDBY modes is possible only
when the RTC clock source is LSE or LSI.
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