LCD issues with green color channel


We’ve got some issues that require someone with a little more knowledge about LCD screens and display settings than myself. First things first, we are working with

  • a Colibri iMX7D 512MB module
  • running WinCE7 (v 1.3b2)
  • with a Riverdi RGB 5" LCD (24 wires)

We have some issues regarding especially the green channel in some of our graphics (mostly waveform). As you can see in the following images, the pure green line (RGB 0x00FF00) is shown correctly on the display (third L as well as top left squiggles). However the two L with combined channels (0xFFFF00 and 0x00FFFF) are showing the wrong color in the vertical portion of the L, the horizontal part is fine. The other green squiggle (not 0x00FF00) you can see a small red-ish trace on the interrupted path.

It should look like this.

I already tried to change some of the display settings, thinking it might have something to do with the timings, but I couldn’t find a solution. The relevant settings should already be visible in the images above, but just for completeness, here’s our settings:

And the Riverdi timings according to their documentation:

This might be a trivial matter for someone more experienced with LCDs but I’m at a loss.

Thank you

Colibri standard permits an 18-bit parallel interface. However, it is feasible to link a 24-bit LCD display to the Colibri iMX7 module using pins that are not compatible with other modules. Hence, can you share details about the carrier board you are utilizing and a schematic snippet concerning the connection to your display?

Hi Alex,

Thanks for your fast reply. Unfortunately, I can’t share any schematics yet, since our partner is the one doing the hardware design for the carrier board. We’ll ask them about a corresponding snippet. However, I can tell you the pins we’re using for the connection to the display:

  • R0-R7 are SODIMM 57, 61, 136, 138, 140, 142, 144, 146
  • G0-G7 are SODIMM 62, 48, 74, 50, 52, 54, 66, 64
  • B0-B7 are SODIMM 76, 70, 60, 58, 78, 72, 80, 46
  • LCD RGB DE 44, HSYNC 68, VSYNC 82 and CLK 56
    So all pins are assigned as per datasheet. I also checked if all are correctly set to lcdif.DATA in the GPIO tool. We already had some issues with the 24bit interface before that you were able to help us with in this post.

As soon as I get schematics and confirmation from our partner, I will post an update. However, I will be on vacation the next two weeks, so it will take a while.

Hi Alex,

Sorry for the long radio silence. Since it is probably a hardware design issue (previous device generation had the same wiring and - at least similar - issues) and a redesign at this stage is not considered feasible right now, we decided to probably drop the issue - unless you have any other ideas on some hidden settings in the registry or the display tool. Thank you for your help nonetheless.

Final update, if anyone else is experiencing similar issues:
Our partner checked the issue again and figured out what’s wrong. In comparison to the previous model, the polarities changed. So once all three polarities (pixel clock, vertical sync, horizontal sync) were set to high, the issue disappeared. Our display is now crisp and without any flickering or artifacts.

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