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Thread: TFT MISO issues continue

  1. #1

    TFT MISO issues continue

    I have a Teensy 3.2 connected to a 3.5" TFT using SPI with ILI9488 driver. The display works fine but when running the graphicstest9488.ino program the code runs but getting data back returns nothing. I'm hoping to get MISO working so i can use my PrintScreen function (which uses ReadPixel() method. Any "common" MISO issues/ fixes with TFT LCD displays like this one?

    Here's what I'm seeing....

    I assume the line, requests data back through the MISO line

    uint8_t x = tft.readcommand8(ILI9488_RDMODE);

    when running the program I get:

    ILI9488 Test!

    Display Power Mode: 0x0

    MADCTL Mode: 0x0

    Pixel Format: 0x0

    Image Format: 0x0

    Self Diagnostic: 0x0

  2. #2
    I think I have the issue solved....

    I have some 2.2, 2.4, 2.8, 3.5" TFT's where MISO outputs data some displays where it doesn't.

    Have a look at the picture, problematic displays
    1. The display on the right does't even have a trace for MISO (nothing on both sides, and i'll guess this boards is 2 layer), the left unit will NOT report back any display info.
    2. The display on the right has a trace for MISO and it works like a million bucks.

    Just an fyi for anyone running into issues where the display will not send info to the MCU. Note this missing MISO connection does not have any effect on the touch capability or the SD card.

    Click image for larger version. 

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  3. #3
    Senior Member+ KurtE's Avatar
    Join Date
    Jan 2014
    Glad you have it resolved. My guess is some displays are either not setup to return this data maybe thinking most people don't read... Or I know with some display chips they don't properly handle that signal, where if connected, you can not use that SPI buss for any other devices that use MISO, so they avoid it. Other boards like ones from Adafruit often add in extra support to allow MISO to work properly on buss with multiple devices.

  4. #4
    Senior Member
    Join Date
    Jul 2020
    Its all too common for MISO not to be connected on cheap displays - and its annoying as most if not all COGs allow pixel values to be read
    back from the frame buffer, so omitting it reduces the functionality of the display.

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