which clock is used when starting the STM32

stm322 · ‎2008-11-10

Posted on November 11, 2008 at 06:34

stm322 · ‎2011-05-17

Posted on May 17, 2011 at 12:51

Hello,

When the STM32 is starting, as long as the RCC hasn't been set up, which clock is used by the processor to start?

Is it the HSI at 8MHz or the LSI at 40kHz or something else?

Also, regarding the figure 8 (Clock tree) of the RM0008 reference manual, the STM32 has 2 different internal clock? HSI and LSI?

Thanks

giles · ‎2011-05-17

Posted on May 17, 2011 at 12:51

I think it uses the HSI at 8MHZ when it starts,

Also, regarding the figure 8 (Clock tree) of the RM0008 reference manual, the STM32 has 2 different internal clock? HSI and LSI?

Yup the LSI is for the independent watchdog, IIRC thats targetting the safety market with its requirements for the watchdog not running on the main clock.

BTW bear in mind if you want to use an external clock if you turn off the HSI you won't be able to do flash writes. :)