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

[hochul yoo]

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.

 

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

But there is one problem that display quaility is not clearly.

And both display devices has exactly same quality.

 

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

Can I get some advice?

Thanks regards

[Erwan SZYMANSKI]

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.

[hochul yoo · Accepted solution]

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.

[PatrickF]

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.