LSE Configuration

Macros
#define	__HAL_RCC_LSE_CONFIG(__STATE__)
	Macro to configure the External Low Speed oscillator (LSE).

Detailed Description

Macro Definition Documentation

__HAL_RCC_LSE_CONFIG

#define __HAL_RCC_LSE_CONFIG

(

__STATE__

)

Value:

                    do {                                       \
                      if((__STATE__) == RCC_LSE_ON)            \
                      {                                        \
                        SET_BIT(RCC->BDCR, RCC_BDCR_LSEON);    \
                      }                                        \
                      else if((__STATE__) == RCC_LSE_OFF)      \
                      {                                        \
                        CLEAR_BIT(RCC->BDCR, RCC_BDCR_LSEON);  \
                        CLEAR_BIT(RCC->BDCR, RCC_BDCR_LSEBYP); \
                      }                                        \
                      else if((__STATE__) == RCC_LSE_BYPASS)   \
                      {                                        \
                        SET_BIT(RCC->BDCR, RCC_BDCR_LSEBYP);   \
                        SET_BIT(RCC->BDCR, RCC_BDCR_LSEON);    \
                      }                                        \
                      else                                     \
                      {                                        \
                        CLEAR_BIT(RCC->BDCR, RCC_BDCR_LSEON);  \
                        CLEAR_BIT(RCC->BDCR, RCC_BDCR_LSEBYP); \
                      }                                        \
                    } while(0)

Macro to configure the External Low Speed oscillator (LSE).

Note

Transition LSE Bypass to LSE On and LSE On to LSE Bypass are not supported by this macro. User should request a transition to LSE Off first and then LSE On or LSE Bypass.

The external input clock can have a frequency up to 1 MHz and be low swing (analog) or digital(*). A duty cycle close to 50% is recommended.

As the LSE is in the Backup domain and write access is denied to this domain after reset, you have to enable write access using HAL_PWR_EnableBkUpAccess() function before to configure the LSE (to be done once after reset).

After enabling the LSE (RCC_LSE_ON, RCC_LSE_BYPASS or RCC_LSE_BYPASS_DIGITAL*), the application software should wait on LSERDY flag to be set indicating that LSE clock is stable and can be used to clock the RTC.

If the RTC is used, the LSE bypass must not be configured in digital mode but in low swing analog mode (*)

Parameters

__STATE__

specifies the new state of the LSE. This parameter can be one of the following values: RCC_LSE_OFF: turn OFF the LSE oscillator, LSERDY flag goes low after 6 LSE oscillator clock cycles. RCC_LSE_ON: turn ON the LSE oscillator. RCC_LSE_BYPASS: LSE oscillator bypassed with external clock. RCC_LSE_BYPASS_DIGITAL: LSE oscillator bypassed with external digital clock. (*) (*) Available on some STM32H7 lines only.