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Author Topic: FT81X Display errors  (Read 4477 times)

Speny

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FT81X Display errors
« on: May 06, 2021, 05:09:16 PM »

Hello All,

I am using a display module that uses the FT813 and seemingly randomly I get a little glitch in the display. I am using an ARM MCU to write commands to the display list using the SPI port and it seems like the its getting an error in the data. For example, instead of drawing a line it may get a dot or rectangle command and draw the wrong image on the display when the swap command is issued.

Examining the waveforms with an oscilloscope the edges seem nice and tight with minimal ringing, it may be an interference issue so maybe I haven't caught a bad frame. The SPI lines only have the display on the bus with no series resistors or capacitors

I wrote a checksum function to read back the display list and make sure the data is correct and that does catch errors, but takes quite a bit more time so I am curious if there is something else I am missing or using a checksum is normal? I could increase the SPI frequency but I have to pass emissions testing so I would like to keep it low for now. 

Has anyone had/solved this issue before? looking for some direction before I get too far down the wrong rabbit hole.

Thanks in advance,
Spencer
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FTDI Community

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Re: FT81X Display errors
« Reply #1 on: May 07, 2021, 12:55:22 PM »

Hi,

Could you post an example display list which shows the issue?

Also, which framework/library are you using to send the commands?

In general, in terms of hardware, the SPI lines should be kept very short (or having the FT813 and the MCU on the same PCB). You may find that the MCU drive strength or slew rate settings help although if the SCK and MOSI and CS look nice and square when measured at the pins of the EVE IC itself then this may not be the issue in this case.

Best Regards, FTDI Community

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