DSI PLL doesn't work with HSI

[Martin Devera]

Posted on March 23, 2017 at 17:49

Hello,

I use DSI with external 25MHz osc. In some design I wanted to use

HSI (is seems supported wrt. ref.manual) but the DSI PLL doesn't

lock at all.

I use IDF=3 to have INFIN=16/3>4MHz and NDIV=125, thus Fvco=666MHz.

ODF=2 (/4) hence DSI clk is 166MHz. All is in correct range.

With HSE, the only difference is IDF=4...

Maybe, HSI is not stable enough ?

M.

#f7 #hsi #dsi

[Martin Devera]

Posted on March 23, 2017 at 18:04

I probably found the reason - when I turn HSE on, DSI PLL uses it even if I

don't set RCC_PLLCFGR.PLLSEL.

Maybe docs is wrong and DSI PLL can't be connected to HSI at all ? It

should be errata then.

[Nesrine M_O · Accepted solution]

Posted on March 24, 2017 at 10:58

Hi

Devera.Martin

,

Please refer to RCC chapter in your related reference manual,Indeed the DSI requires the use of the HSE (high-speed external) oscillator as clock input for DSI PLL.

I recommend you also to refer to the

http://www.st.com/content/ccc/resource/technical/document/application_note/group0/1d/b8/33/4f/dc/0a/45/52/DM00287601/files/DM002876pdf/jcr:content/translations/en.DM002876pdf

aboutDSI Host on STM32F4 Series and STM32F7 Series microcontrollers.

-Nesrine-

[Martin Devera]

Posted on March 24, 2017 at 12:24

Dear Nesrine, Thanks a much for the confirmation. I didnt found AN4860 before. Can you tell where is the picture

above copied from ? I can't find it in my PDF.

In Reference Manual there for STM32F76XX is explicitly listed ''HSE or HSI''. See below.

Maybe it is documentation bug ?

M.

[Nesrine M_O]

Posted on March 24, 2017 at 12:58

Hi

Devera.Martin

,

The pictrue is copied from the DSI chapter on theSTM32F469/479 refrence manual :

http://www.st.com/content/ccc/resource/technical/document/reference_manual/29/77/09/5a/b1/60/4e/bd/DM001275pdf/files/DM001275pdf/jcr:content/translations/en.DM001275pdf

-Nesrine-