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Peter Osucha

I have two graphic displays (a 5 and 7in version of essentially the same version. 

  1. NHD-5.0-800480FT-CSXP-CTP
  2. NHD-7.0-800480FT-CSXV-CTP

I'm simply trying to read the chip identification code based on the FT81 example software.  I've verified my SPI comm (which is using a modest 3MHz SPI clk).  However, I never get a non-zero response.  I'm using the ZIF-style connector and have confirmed the connector pinouts, 3.3V is present, etc.  Any suggestions?  Seems odd to me I never even get the cid (on either display).

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  • Peter Osucha
    • Edited

    Getting familiar with the posting options so please forgive my first attempts.  The functions are pretty straightforward and as mentioned, I do see the correct 8 characters in the 'sendBuff' being sent on the SPI comm.

    The 'Read Chip Identification Code' function is in pic 1 and the GD_rd32() function is in pic 2.

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  • Peter Osucha

    One more in the event someone sees each post before responding.  Do I need to have voltage applied to the backlight in order to communicate with the displays?  I've been assuming that pins 17-18 need power for the display to be usable but not to be able to communicate with the FT81 (and get a SPI response).

     

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  • Peter Osucha

    In case someone follows this thread in the future...

    No, you don't need power applied to the backlight to communicate with the display.  I am getting the 0x7C response from the display by reading the 0x302000 register as stated in the datasheet.  However, only in an odd situation.

    To get a response, I need to swap the MISO/MOSI lines, send data over the SPI connection, then swap them back to the correct configuration.  This is 100% repeatable but I have no idea why.  Obviously, this isn't a workable solution but it at least shows me a response.

    Second if I apply 3.3V power to the backlight, I never get any response which likewise isn't workable.  I'll keep playing with the display to see what else I can learn.

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  • Engineering Support
    Community moderator

    Hi Peter,

    Thank you for the detailed information. I wanted to clarify if your SPI protocol is following this timing diagram?

     

    I also wanted to provide the programmer's guide for this chip if you haven't got it already just in case you find it useful here:

    https://www.ftdichip.com/Support/Documents/ProgramGuides/FT81X_Series_Programmer_Guide.pdf 

     

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  • Peter Osucha

    Thanks for the response.  Yes, the SPI protocol is following that diagram and the SPI clock frequency is below the 30MHZ limit (I've used 2MHz but also 25MHz).  I do have the programmer's guide and it has been useful (certainly).  

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