STM32WB09XE datasheet(17/73 Pages) STMICROELECTRONICS

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Figure 6. Clock tree

RCC_LCOSEL

/1, /2, .., /32

LSI RCO

32 KHz

RCC_LCO

LSE OSC

32 KHz

RCC_OSC32_OUT

RCC_OSC32_IN

OSC_OUT

OSC_IN

HSE OSC

32 MHz

SYSCLKPRE

/1, /2, .., /32

CLK_16MHz/512

CK_RTC,

CK_WDG,

CK_BLEWKUP

HSI RCO

+ PLL

64 MHz

HSESEL

SYSCLKDIV

SYSCLKPRE

/1, /2, .., /64

CLKSLOWSEL

HSISEL

CLK_TIM2,

CLK_TIM16,

CLK_TIM17

CLK_SYS

to CPU,

AHB0,

APB0,

APB1,

SRAM,

PKA

SMPSDIV

CLK_16MHz

HSESEL

CLK_SMPS

CLKANA_ADC

CLK_SMPS

CLK_SYS

HSE

HSI

CLK_16MHz/512

LPUCLKSEL

CLK_LPUART

LSE

CLKANA_ADC,

CLK_USART,

CLK_I2C,

CLK_BLE16,

CLK_FLASH,

CLK_PWR,

CLK_RNG

BLECLKDIV

CLKSYS_BLE

CLK_32MHz

HSESEL

CLK_BLE32,

CLKDIG_ADC

CLK_16MHz

CLK_SYS

SPI3I2SCLKSEL

CLK_SPI3/I2S

RCC_MCO

RCC_MCOSEL

It is possible to output some internal clocks on external pads:

•

The low speed clocks can be output on the RCC_LCO I/O

•

The high speed clocks can be output on the RCC_MCO I/O

This is possible by programming the associated I/O in the correct alternate function.

Most of the peripherals only use the system clock except:

•

I2C, USART: they use an always 16 MHz clock to have a fixed reference clock for baud rate management.

The goal is to allow the CPU to boost or slow down the system clock (depending on on-going activities)

without impacting a potential on-going serial interface transfer on external I/Os

•

LPUART: always uses a 16 MHz clock or LSE to have a fixed reference clock for baud rate management.

The goal is to allow the CPU to boost or slow down the system clock (depending on on-going activities)

without impacting a potential on-going serial interface transfer on external I/Os.

•

SPI: when using the I2S mode, the baud rate is managed through the always 16 MHz or always 32 MHz

clock or system clock (CLK_SYS) to reach higher baud rates. When running in other modes than the I2S,

the baud rate is managed by the system clock. This implies its baud rate is impacted by dynamic system

clock frequency changes.

•

TRNG: in parallel with the system clock, the TRNG uses an always 16 MHz clock to generate at a constant

frequency the random number whatever the system clock frequency

STM32WB09xE

Functional overview

DS14210 - Rev 6

page 17/73

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