Clocks

AN4325

12/27

DocID024966 Rev 1

2

Clocks

Different clock sources can be used to drive the system clock (SYSCLK):



HSI 8 MHz RC oscillator clock (high-speed internal clock signal)



HSE oscillator clock (high-speed external clock signal)



PLL clock

The devices have other secondary clock sources:



40 kHz low-speed internal RC (LSI RC) that drives the independent watchdog and,

optionally, the RTC used for auto-wakeup from the Stop/Standby modes.



32.768 kHz low-speed external crystal (LSE crystal) that optionally drives the RTC



HSI 14MHz RC oscillator (HSI14) dedicated for ADC

Each clock source can be switched on or off independently when it is not used, to optimize

the power consumption. Refer to RM0360 reference manual for a description of the clock

tree.