Color artifacts on display (SPI+18-bit RGB) using ST7701s driver

[HP]

Hi!

I'm getting 2 round displays up and running using tGFX on an STM32F767 (custom board, external SDRAM and QSPI)

I think almost everything is running but I have some weird artifacts. the clearest I can show is the color wheel test.

While the image is 24-bit and the display is 18-bit I wonder why I see the clear lines across the display (Please disregard the red stripe horisontally - that's a smudge on the protective film)

To me it would seem like something like a rounding of the color information but that would make much more sense if I was coming from less than 18-bit.

Anyone who can offer some insights here or point me in a direction? I tried with a real image and certain colors just get REALLY wonky..

[HP]

so - on the testimage (the one with all the 'test' on it) the two lines beneath the white bar was supposed to be a grayscale bar, one in each direction.

[HP]

Here's another example - it's really not good :\

[HP · Accepted solution]

Aaand it's solved 🙂

This was due to the pixel polarity - it was inverted.

Fun fact - when debugging this you can break the processor and play around with the bit settings in the SFR tab. it was working wonders for me!

[KAgga.1]

Hello @HP ,
I'm also facing an issue while interfacing ST7701s RGB+SPI(9-Bit) based display. Well, I'm able to properly interface RGB only display.
Could you help by sharing the configuration or demo project for it.

Regards,
Keshav Aggarwal

[Msolinas]

Hi kagga.1, can you share your initalization? I can't start my display in no way... thanks.

[KAgga.1]

PFA

[Msolinas]

Thanks for your reply and code. In the code is not present the SPI mode initialization, can you clarify if is 9 bit or 16 bits? I adopted the gpiospi type, but no fortune for me. My interface not start in every mode possible. My display is 800x480 in horizontal position. Thanks for your help.

[KAgga.1]

It's 9 bit.

[Msolinas]

thanks