SPI problem with NHD-3.5-320240FT-CSXN-CTP

Wiggum

Hi all,

I have a problem with above mentioned display.
My setups are
1. TFT connected via MPSSE to PC, MSVC software
2. TFT connected to custom board with TI Tiva 1294 uC
 2.1 using a modified "simple app" with customized hardware layer
 2.2 using exported EVE Screen Designer projects with own hardware layer for the Tiva

For comparison, I also have a VM810C50A-D evaluation board from FTDI

A. The VM810 board runs flawlessly in all configurations.

B. I had to fumble around a lot with the NHD TFT to get it to work. Firstly, with the MPSSE cable and the sample app, I had to reduce SPI speed from 12MHz to 1.2 MHz but also then, it was not stable in all cases.
By accident, I found out that when I reduce the supply voltage from 3.3V to 2.9V, the NHD display worked even at 12MHz SPI speed.
At voltages above 3.3V, it does not even read the 0x7C code correctly.

For the custom board, it's almost the same scenario, however it is rather unstable and does not carry out commands, so the display app get's stuck at waiting for the cmd write and read pointers to match.

Am I doing anything wrong? Do others see this behaviour as well?

Any help is greatly appreciated.

Best regards,

Rainer

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Comments

11 comments

Date Votes
  • Ted M.
    NHD Staff

    Hi Rainer,

    The MPSSE cable may not supply enough current to drive the display and the backlight on it's own.  Please describe how the display is receiving power in your configuration. 

    Try connecting this display to an Arduino using our NHD-FT81x-SHIELD for easier prototyping.  It has a built in Buck regulator that will supply the proper power to the display and also drive the backlight.

    https://newhavendisplay.com/content/userguide/NHD-FT81x-SHIELD_User_Guide.pdf

    Best Regards,
    Ted

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  • Wiggum

    Hi Ted,


    thanks for your response. The MPSSE cable can indeed not drive the current. That's why I am using an external power supply (connecting the GNDs, of course).
    With that, I was able to reduce the supply voltage to 2.9V and see that it works, there.

    The MPSSE is not my main concern. It is our custom board with the Tiva processor.
    Comparing the NHD circuit with that on the VM800 board by FTDI, I see buffers (74LCX125) on the FTDI board which are not used on the NHD board.
    I am suspecting that it's the SPI communication.
    As said, the FTDI display works flawlessly in all our configurations.

    I am digging into this and will report but would appreciate any hint.

    Best regards,

    Rainer

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  • Ted M.
    NHD Staff

    Hi Rainer,

    The added buffers (74LCX125) on the FTDI board allow the SPI master and slave interface of the FT8xx to be 5v tolerant. 
    Our board will support the 3.3v SPI interface and is not 5v tolerant. Thanks for your input and let us know what you find.

    Best Regards,
    Ted

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  • Wiggum

    Hi Ted,

    BTW: Did you ever test the MPSSE cable communication?
    Your example projects on github are only configured to your modules correctly for the Arduino platform.

    Best regards,

    Rainer

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  • Ted M.
    NHD Staff

    Hi Rainer,

    Unfortunately we have not tested this using an MPSSE interface.  If you find any issues using this type of interface, please report them here for us to help.

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  • Wiggum

    Hi Ted,

    sure. Have a look at my initial posting.

    I had to reduce the power supply to 2.9V to run stable.

    Best regards,

    Rainer

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  • Wiggum

    Hi Ted,

    are there any news regarding this issue?
    Our customer who will release a series of units with this display is getting a little nervous about it.
    On their end, they can't get the MPSSE solution working at all.
    Would it be possible to check SPI stability with different setups?

    Otherwise, we'd have to look for different solutions right now.

    Best regards,

    Rainer

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  • Ted M.
    NHD Staff

    Hi Rainer,

    Please take a look at the Github libraries posted on this forum by lightcalamar using our EVE2 boards and running with other hardware platforms.
    https://github.com/lightcalamar/GD23Z/blob/master/README.md
    These may be of help as a reference to get the SPI working with the Tiva micro. Please let us know if this library is helpful to get you going.

    Ted

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  • Wiggum

    ... hard to get through.

    My problem is not the software layer on the Tiva. That's already working. As I explained before: with an evaluation board from FTDI, this is working perfectly.

    I would like to see if _you_ can get the display to work with the MPSSE adapter with the sources _you_ provided.
    I adapted your sources from gitbub to have the appropriate parameters for the NHD board. Here, at my place (and at our customer's), this is not working well.
    Again, I have to say that the FTDI evaluation boards work perfectly with MPSSE. The complete demo application is running through all stages

    Sorry for nagging, but this is quite an important issue.

    Best regards,

    Rainer

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  • Ted M.
    NHD Staff

    Hi Rainer,

    Please email me the source code you are using with the FTDI MPSSE adapter as well as the wiring diagram for the display interface and we will review them to see if we can help determine what is causing the stability issue you are seeing.  nhtech@newhavendisplay.com

    Best Regards,

    Ted

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  • Ted M.
    NHD Staff

    As an update to this topic - This issue was resolved by adding a hardware buffer to the SPI clock signal at the MPSSE cable.

    Best Regards,

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