TFP401: Color issues with 8 bit LCD from PC HDMI Source

Gregory Peck

Part Number: TFP401
Other Parts Discussed in Thread: DS90C383

We have built a customer HDMI board based on the TFP401 IC with LVDS out using the DS90C383 LVDS transmitter. We are connecting to a standard Windows 10 laptop for an HDMI source. On 6 bit (3 stream) LCD the color are displayed correctly. We have a customer that tried to use our board on the attached 8 bit (4 stream) LCD reading the EDID directly from the panel and the colors are off. We have reviewed the color mapping from the 401 to the 383 and they are following the correct MSB pattern. We are stumped as to why the 4th stream is causing the color issues in the photos.

Note: if we disconnect the 4th link (essentially 6 bit data) the colors are fine but the panel is 25% of normal brightness.

8 bit image then 6 bit (dark image)

over 6 years ago

0 Gregory Peck over 6 years ago

Prodigy 60 points

1-180500-1 AM-1280800N3TZQW-00H.PDF

0 Joel Jimenez0 over 6 years ago in reply to Gregory Peck

TI__Mastermind 18655 points

Hello Gregory,

I'm reviewing your question. I will be back with my feedback tomorrow.

Regards

0 Gregory Peck over 6 years ago in reply to Joel Jimenez0

Prodigy 60 points

slla325a.pdfHi thanks Joel,

Note that after a lot of digging we are thinking that the issue may be the incoming HDMI data which from a standard PC running Windows 10 has data the serializer does not properly align on the 4th channel causing the display colors to misalign the MSB data. We saw this note below and have been able to test the panel at 16 bit color depth without a problem with the same wiring. It seems that this IC is DVI limited to 24 bits. So what would happen if we have a 32 bit HDMI feed?

From the Design Guide

4. The incoming TMDS data must be DVI-compliant, and not contain HDMI island data (e.g. audio)

or deep color (more than 24 color bits).

0 Gregory Peck over 6 years ago in reply to Gregory Peck

Prodigy 60 points

Joel,

I may have been premature on stating that 16 bit color pallet is displaying correctly. The board designer stated this but on my new Ubuntu build with a reduced pallet (65K colors) they are closer but not a match see image below. The OS also was later set to 24 bits what the panel expects but then the colors are not even close. The same issue that was originally shown.

0 Joel Jimenez0 over 6 years ago in reply to Gregory Peck

TI__Mastermind 18655 points

Hello Gregory,

Could you provide the schematics ?

Is it possible for your using a video generator or finding a way to set individually the colors red, green and blue in the source and then monitor the TFP401 parallel outputs? I would need to confirm if your implementation has signal integrity issues.

Regards

0 Gregory Peck over 6 years ago in reply to Joel Jimenez0

Prodigy 60 points

Yes I'll pull them from our designer Monday.

0 Joel Jimenez0 over 6 years ago in reply to Gregory Peck

TI__Mastermind 18655 points

Gregory, Do you have any feedback here?
Regards

0 Gregory Peck over 6 years ago in reply to Joel Jimenez0

Prodigy 60 points

Hi Joel,

I think we figured out our issue. We followed a document from TI on the proper mapping for 24 bit with and new panel we discovered that it followed VESA mapping not LDI. See my attached details and see if you agree. The old mapping had the MSB's shifted into the LSB slots. We are spinning a new board for final test and will confirm if this resolves the issue.

Last question: Do you have a suggestion on a MUX to use to switch between modes?

TFP401 24bit issue.pptx

0 Joel Jimenez0 over 6 years ago in reply to Gregory Peck

TI__Mastermind 18655 points

Hello Gregory,

Sorry, we are not familiar with the TI's MUX portfolio. You can use any CMOS/TTL 2:1 data selector.

Regards,
Joel

Interface

Interface forum

TFP401: Color issues with 8 bit LCD from PC HDMI Source