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AD9889 video noise on the display

I got the AD9889 HDMI transmitter working, but I see noise on the display. I generate a color bar as a source image, I see a couple of verticle noise striped on some of the colors. If I wiggle the HDMI cable the noise changes.

I started playing with the register settings and first I noticed that the set provided on the web doesn't work. It also does not match the programming guide documentation. One example is register 0x98. The documentation says must write a 7 to this register. The example code says write 178. But I only got a display working by writing a 170. Registet 0xAF also affects the noise on the display. A value of 6 works best, while a value of 4 makes the video break up once in a while. And last but not lease, I had to increase the drive strength registers 0xA2 and 0xA3 to 255 to minimize the noise on the display.

My resolution is 1280x1024, 108MHz clock, 60Hz frame.

Can someone provide me a register settings that work for this resolution that is different than the one available from the web?

I'm attaching the register setting programming that gives me the best results. This is a read back from all registers.

Thanks,
Ed.

best_settings.txt.zip
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  • I checked the new register settings. It makes no difference. The only difference I see is on the drive strength registers 0xA2, 0xA3. If I program to 0x87, it gets worse. If I leave it at 0xFF, it gets better. It almost indicates that it want maximum signal strength on the cable.

    I also tried a difference cable. I used a micro-to-full HDMI adapter, and then a very thick and expensive HDMI cable. It was actually more noisy than using a thin micro-to-full HDMI cable.

    I want to understand more about the register 0x42 bit 5 that's not set. What does it mean? Do I need a termination on the board?

    Let me know if you see any issues on the layout and schematics I sent.

    Ed.

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  • I checked the new register settings. It makes no difference. The only difference I see is on the drive strength registers 0xA2, 0xA3. If I program to 0x87, it gets worse. If I leave it at 0xFF, it gets better. It almost indicates that it want maximum signal strength on the cable.

    I also tried a difference cable. I used a micro-to-full HDMI adapter, and then a very thick and expensive HDMI cable. It was actually more noisy than using a thin micro-to-full HDMI cable.

    I want to understand more about the register 0x42 bit 5 that's not set. What does it mean? Do I need a termination on the board?

    Let me know if you see any issues on the layout and schematics I sent.

    Ed.

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