ST STM32F31xx User Manual

UM1581
Reset and clock control (RCC)
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18.2 RCC Firmware driver API description
The following section lists the various functions of the RCC library.
18.2.1 RCC specific features
After reset the device is running from HSI (8 MHz) with Flash 0 WS, all peripherals are off
except internal SRAM, Flash and SWD.
 There is no prescaler on High speed (AHB) and Low speed (APB) busses; all
peripherals mapped on these busses are running at HSI speed.
 The clock for all peripherals is switched off, except the SRAM and FLASH.
 All GPIOs are in input floating state, except the SWD pins which are assigned to be
used for debug purpose.
Once the device starts from reset, the user application has to:
 Configure the clock source to be used to drive the System clock (if the application
needs higher frequency/performance).
 Configure the System clock frequency and Flash settings.
 Configure the AHB and APB busses prescalers.
 Enable the clock for the peripheral(s) to be used.
 Configure the clock source(s) for peripherals which clocks are not derived from the
System clock (ADC, TIM, I2C, USART, RTC and IWDG).
18.2.2 Internal-external clocks, PLL, CSS and MCO configuration functions
This section provides functions allowing to configure the internal/external clocks, PLL, CSS
and MCO.
1. HSI (high-speed internal), 8 MHz factory-trimmed RC used directly or through the PLL
as System clock source. The HSI clock can be used also to clock the USART and I2C
peripherals.
2. LSI (low-speed internal), 40 KHz low consumption RC used as IWDG and/or RTC
clock source.
3. HSE (high-speed external), 4 to 32 MHz crystal oscillator used directly or through the
PLL as System clock source. Can be used also as RTC clock source.
4. LSE (low-speed external), 32 KHz oscillator used as RTC clock source. LSE can be
used also to clock the USART peripherals.
5. PLL (clocked by HSI or HSE), for System clock.
6. CSS (Clock security system), once enabled and if a HSE clock failure occurs (HSE
used directly or through PLL as System clock source), the System clock is
automatically switched to HSI and an interrupt is generated if enabled. The interrupt is
linked to the Cortex-M4 NMI (Non-Maskable Interrupt) exception vector.
7. MCO (microcontroller clock output), used to output SYSCLK, HSI, HSE, LSI, LSE,
PLL clock on PA8 pin.
 RCC_DeInit()
 RCC_HSEConfig()
 RCC_WaitForHSEStartUp()
 RCC_AdjustHSICalibrationValue()
 RCC_HSICmd()
 RCC_LSEConfig()
 RCC_LSEDriveConfig()
 RCC_LSICmd()

ST STM32F31xx Specifications

General

Brand	ST
Model	STM32F31xx
Category	Microcontrollers
Language	English