PTN3460: image with jitter, not stable

[stefan01]

Hi everyone.

I use a PTN3460 to convert 1280x480 to LVDS. But the image I get has some weird fringes, as if the lines are not perfectly aligned on the visible area, but slightly moved left/right. 

The image is distorted and moving about, the lines that are out of place are not the same with every refresh of the image. This does not happen if I use DVI and the TFP401, only with DP and PTN3460 the problem occurs.

Any ideas why this is happening, and how to get rid of the problem?

[stefan01]

That is not correct, or I understood you wrong. The PTN3460 is set for I2C master with boot strap resistor. After I release the reset line, it is requesting 128 byte of EDID and 128 byte of config data. The first 128 byte are the EDID bytes I recovered from the working HDMI converter board. 0x84 is set to 1.

So in my opinion, there should not be a difference from a video card's point of view. In both cases, the same EDID information is being transmitted to the video card. And yet the result is different?

[stefan01]

Hi Tomas,

I do not have the specification for the panel. The only thing I have is an EDID, that works on a converter board. This board uses an ADV7611 (HDMI) with an DS90C385 for converting to LVDS. On this board, the EDID works. I think the actual EDID is confidential.

Is there a difference between HDMI and DP, when using the same EDID file? What should I look for in the EDID, which could cause this behaviour?

Best regards

[TomasVaverka]

Hi Stefan,

The HDMI monitor (or VGA monitor) is a multi-sync display which means it can support/display many different native resolutions such as 1080p, 800x600 …etc.

LCD panel only supports one native resolution as defined in the LCD panel specification.

So EDID for LCD panel needs to specify only one resolution supported in it, so DP source will emulate all resolutions using one resolution timing (such as using 1080p timing to emulate other resolutions).

EDID for HDMI monitor (or VGA monitor) can have many native resolutions in it, so that DP source can just output different resolutions to the display (such 1024x768 in BIOS mode, and 1080p in Windows OS).

In short, EDID good for HDMI display may not be good for LCD panel which need to check EDID contents.

Best regards,

Tomas

[TomasVaverka]

...missed one point.

LCD panel EDID should not have Established Timings and Standard Timing supported in it, but only Preferred Timing (Detailed timing) is supported.

You can download EDID spec from VESA.org (membership required) to know detail contents of EDID data.

Best regards,

Tomas

[stefan01]

Maybe there's a misunderstanding here.

The HDMI monitor is not a monitor you can buy in one piece. It is just a panel from Sharp, and from another vendor the board containing both ADV7611 and DS90C385. The ADV takes care of the EDID emulation, and that's where I got the (working) EDID from. This setup is working, so imho the EDID must be advertising the correct data to the PC.

The question is, why is the same EDID not working on the PTN3460? Is there a difference between HDMI and DisplayPort regarding the data in the EDID?

[TomasVaverka]

Hi Stefan,

I think  most likely HDMI panel (like eDP panel) has t-con in it, so it is multi-sync display.

If you can provide us the HDMI panel specification, then we can check whether it has t-con it.

EDID describes display characteristics, so the DP source (PC) can know how to prepare video timing/resolution for the display.

PTN3460 will not do anything on EDID, and just pass it to the DP source(PC).

Please check EDID contents to be sure that “Established Timings and Standard Timing” are not supported in the EDID, and only Preferred Timing (Detailed timing) is supported.

Best regards,

Tomas

[TomasVaverka]

Hi Stefan,

It looks like the LVDS pixel clock is not correct for the LCD panel.

Could you please share  your LCD panel specification and EDID data used for 1280x480 resolution?

Best regards,

Tomas