NHD-5.0-800480TF-ATXL#-CTP VS. NHD-7.0-800480EF-ASXN#-CTP

mike_s

Hi All,

I have a current project using an STM32H7 micro, which has a built-in LTDC display controller.  I have it working fine with the 5.0" display as mentioned in the topic.

I wanted to then see how much better it would be with the 7.0" display, which appears to be an identical electrical interface, with the exception of the LCD Backlight voltage being 9.6V on the 7.0" versus 19.2V on the 5.0".

I realize the controller chips changed:

1) 5.0" ==  ILI6126C
2) 7.0" == HX8264-D02

I tried the 7.0" display on both of my boards (which both work fine with 5.0" displays), and I get absolutely nothing on the screens except for the initial white backlight when it first boots up...

I've played with the timings, I/O drive strength, pixel clock, etc, with zero effect. 

I did notice that the PCLK on the 5.0" says it's rising edge triggered, versus the 7.0" which is falling edge triggered.. but I haven't tried inverting the PCLK polarity yet, do I need to make that change for the 7.0" TFT?

Is anyone aware of anything else that may need to be changed when going from the ILI6126C controller to the HX8264??


(I've opened an RMA request suspecting that the display may be bad, but I realize they do test these screens before they are shipped out, so I wonder if there is still something I'm missing???)


Thanks so much,

- Mike

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Comments

5 comments

Date Votes
  • John_Dailey

    Actually,

    I think I see something, I'll be trying this today when I get home from work...

    1) PCLK needs to be inverted for this LCD

    2) ** most ** important, sounds like this 7.0" TFT is setup by default to use 'DE' mode, whereas the 5.0" probably was not?

    (my LTDC controller does have the DE pin, but by default it was setup as 'active LOW', and I have the pin pulled down), so it sounds like the 5.0" was probably not using it which is why my setup still worked, but the 7.0" I need to switch the pin polarity)


    Ie I see a discussion just like this in a old thread from 2014..

    https://support.newhavendisplay.com/hc/en-us/community/posts/10985916952471-NHD-7-0-800480EF-ATXL-CTP-dead-


    I'll report back after testing this evening 

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  • John_Dailey

    Ok,

    I got it all working... the DE POLARITY was backwards, at least according to the STM32H7 datasheet, so I don't know whom is right, the NewHaven TFT datasheet, or the STM32H7 datasheet.

    But in order for DE to work, I had to set:

    ** From the STM32H7 datasheet **

    DEPOL: not data enable polarity
    This bit is set and cleared by software.
    0: not data enable polarity is active low.   <<<==== had to set to ACTIVE LOW
    1: not data enable polarity is active high.

    with it ACTIVE HIGH there is NO display.... only thing I could do to prove it out would be to scope it up, but right now I just want to install the screen and get it working.

    (I also verified I could disable DE altogether by installing that R4 short, which I did to verify the screen worked, then removed it, as I want to use the default of 'DE' being enabled.


    So for now the screen works!  But I'm concerned as to which vendor is right... is the STMicro datasheet backwards, or is the datasheet wrong for the LCD, and 'DE' is actually ACTIVE LOW, not high?

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  • Ted M.
    NHD Staff

    Hi Mike_S,

    It's good to hear you have it working!

    You are correct that the 7.0" TFT is setup to work in DE mode by default.  The display's Data Enable mode is Active High at pin 34 to enable the data input bus.

    Best Regards,

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  • mike_s

    Hi Ted,


    If you all are certain that the pin34 DE is definitely ACTIVE HIGH logic, then that means STMicro messed up their data sheet, since I had to set the LTDC -> DE polarity to 'Active Lo'....

    but of course their wording could also be a 'double negative', when they say 'not data enable polarity is active low'... which would mean Active Hi. LOL

    anyhow, this is good info for anyone that ends up using an STM32xxx processor with the LTDC controller, so they know the datasheet is backwards...

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  • mike_s

    Finally,

    7.0" TFT is working perfect, thanks so much, I have both 5.0" and 7.0" working awesome!

    BTW, also verified that the 'Data Enable' is indeed 'ACTIVE HIGH', so STMicro has an error in their datasheet..

    here's the scope shot, showing DE active high and a bit of the RBG data lines...

    (DE ==> Yellow)
    (RBG bit ==> Green)

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