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hochul yoo
Visitor II
September 2, 2022
Solved

STM32MP1) Can I duplicate LTDC(RGB) signal for dual display?

  • September 2, 2022
  • 2 replies
  • 2517 views

Hi all ~

I have a question regarding dual display.

I want to display same content at the same time to both display devices (LTDC and HDMI).

But, As my understanding, STM32MP1 has only one display controller.

https://community.st.com/s/question/0D53W00000DH4AqSAL/can-i-use-dual-display-on-stm32mp157c-chipset

My TFT-LCD's resolution is 1280x800 (10.1inch) and support LVDS.

So, if I can implement dual display, LCD and HDMI will has same resolution.

Isn't there any solution to implement dual display implementation?

Actually, I tried the following.

0693W00000SuMFqQAN.png 

As a result, both display devices can be display same content at the same time.

0693W00000SuLhoQAF.jpgBut there is one problem that display quaility is not clearly.

And both display devices has exactly same quality.

0693W00000SuLr5QAF.jpg 

To be honest I don't know exactly that this application is right.

Can I get some advice?

Thanks regards

    This topic has been closed for replies.
    Best answer by hochul yoo

    I solved this problem.

    I changed all of LTDC pin`s maximum output speed to Very High in the CubeMX.

    Now both display quality are very clearly.

    2 replies

    E
    Erwan SZYMANSKI
    Technical Moderator
    September 2, 2022

    Hello @hochul yoo​ ,

    Thanks for your contribution.

    In fact, our platform is not really designed to use dual display. As you said in your post, you have a possibility to do like you did, but you will always have a quality issue.

    Why ?

    Because it will only works with 2 identical panels/display (or at least, 2 display that has the same specs in term of pixel clock, padding, polarity etc etc...). As you use 2 different displays, you will not be able to tackle this quality issue.

    I hope it will help you in your development.

    Kind regards,

    Erwan.

    H
    hochul yooAuthorAnswer
    Visitor II
    September 29, 2022

    I solved this problem.

    I changed all of LTDC pin`s maximum output speed to Very High in the CubeMX.

    Now both display quality are very clearly.

    P
    PatrickF
    Technical Moderator
    September 29, 2022

    Hi @hochul yoo​ ,

    Nice to see your got a working platform.

    Be careful that LTDC is a parallel interface, so many pins toggling simultaneously which could strongly affect supply noise if output speed is over-set and if lines load are high (i.e. long wires/connectors/etc...).

    Please refer to AN5031 I/O speed settings recommendations as well as DS12505 IO output timing characteristics.

    Bear in mind that as LTDC is single-data-rate, the data lines are toggling half the frequency of the clock, so usually deserve a lower IO speed setting than clock.

    In your case, it is also strongly recommended to use an external oscillator to feed the HSE clock input. See also ES0438 for details.

    Regards.

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