STM32f429I LTDC Clock Value Problem

[Kasapoglu.Orkun]

Posted on May 02, 2016 at 10:50

Hi. I'm trying to set LTDC clock to 54MHz but I am measuring 385.7kHz instead of the true value with oscilloscope. Scope has 350 MHz bandwidth.

I'm configuring the PLLSAI with std_periph libraries;

RCC_PLLSAIConfig(432, 2, 2);

RCC_LTDCCLKDivConfig(RCC_PLLSAIDivR_Div2);

RCC_PLLSAICmd(ENABLE);

while(RCC_GetFlagStatus(RCC_FLAG_PLLSAIRDY) == RESET) {}

Am I missing something?

Thanks.

[Walid FTITI_O]

Posted on May 02, 2016 at 18:24

Hi kasapoglu.orkun,

First, take into account that for STM32F429, the LTDC clock output frequency is limited to 42MHz as mentioned in its

http://www2.st.com/content/ccc/resource/technical/document/datasheet/03/b4/b2/36/4c/72/49/29/DM00071990.pdf/files/DM00071990.pdf/jcr:content/translations/en.DM00071990.pdf

(Table107. LTDC characteristics)

I suggest that you refer to the LTDC examples in  

http://www2.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/stm32-embedded-software/stm32-standard-peripheral-libraries/stsw-stm32065.html

(since you are using it) ; LTDC_Display_1Layer as example where you can reconfigure the PLLSAI perscalers to get you desired frequency. The example is under the following path:

STM32F4xx_DSP_StdPeriph_Lib_V1.7.1\Project\STM32F4xx_StdPeriph_Examples\LTDC\LTDC_Display_1Layer

-Hannibal-