STM32F3-Discovery HSI clock source

[kvresto]

Posted on April 27, 2016 at 04:52

Hi.

My stm32F3-discovery does not have an external crystal(HSE) fitted to it.

I set up a new project with CUBE and according to CUBE clock configuration figure, the MAX clock speed I can achieve with HSI(8Mhz), is PLL(64Mhz).

Is this correct, because I seem to remember a post I read and cannot find anymore, that even when using HSI(8Mhz) the F3 can be configured for 72Mhz??

Can someone clear this up please. An example as to how to setup the F3 would be fantastic.

kvresto

[kvresto]

Posted on April 27, 2016 at 08:36 Also is there a way of to output the PLL clock currently selected on an I/O pin to view with my CRO? I've found the RCC example but I don't think it will output the PLL freq. thanks

[Tesla DeLorean]

Posted on April 27, 2016 at 08:38

Isn't there an 8 MHz presented by the ST-LINK part for the express purpose of providing an HSE input?

It should be apparent from the manual if 64 MHz is the highest support, it's not a part I'm actively using so you'll need to check yourself. The F1 parts were definitely limited, due to the need to half the HSI as input to the PLL, and the PLL multipliers available.

[Tesla DeLorean]

Posted on April 27, 2016 at 08:41

There is the MCO (PA8) pin, the manual should clear define what clocks you can see there, the PLL would be available if you have it selected as a source for the system.

The ST-LINK part uses it's MCO (PA8) pin to provide an 8 MHz output of its HSE crystal. Should be routed by default as I recall, or via some solder bridge (SB) options. Review DISCO user manual w/schematic.

[kvresto]

Posted on April 27, 2016 at 10:23

Your absolutely right clive. I just looked at the schematic, and confirmed this in the startup file.

#define

PLL_SOURCE_HSE_BYPASS

// HSE bypassed with an external clock (8MHz, coming from ST-Link) used to clock

I never looked before today, and always assumed it was using HSI.

Thanks again Clive

kvresto