But we are getting white dots in the mp4 pictures

Hi George,

According to the Recommended Operating Conditions of the datasheet, the SN75LVDS82 requires a differential input voltage between 0.1V and 0.6V. The 1.8V coming from the i.mx8mplus does not follow the specifications, which is most likely leading to the white dots you are seeing.

Best,

Nikolas

"LVDS1.8" means that the pins are supplied by 1.8 V; the actual output voltages still are LVDS, i.e., generate ±350 mV over the 100 Ω termination.

Please show the schematic, and checke the LVDS waveforms with an oscilloscope.

??? Who is correct ??

Clemens or Nikolas ???

Hi George,

Please refer to the i.mx8plus's datasheet and let me know what the output voltages are. We can then proceed forward with the issue you are seeing on the FPD-Link part. 

White dots are a byproduct of something related to the power supplies (or noise on the power supplies). Please check that the power supplies are functioning correctly by probing the power rails.

Best,

Nikolas

1.

2. imx8mplus's spec shows it takes 1.8VDS input only:

3. output from imx8mplus's LVDS

Regards,

George

1. receiver end is 1.34VDC with 360mV LVDS signals

Hello George,

Clemens' most recent response is accurate and for clarity's sake I am streamlining the flow of this thread.

Revisiting the white dots you are seeing on the output, white dots are sometimes a byproduct of something related to the power supplies (or noise on the power supplies). Please check that the power supplies are functioning correctly by probing the power rails.

Best,

Nikolas

picture color dots

When you move the video player window, do the dots move together with the window? If yes, then this problem definitely happens before the i.mx8 outputs the LVDS signal.

It appears that the white dots happen at some places with high contrast. This looks like a problem with the video decoder.

picture 1 is from the HDMI output, there is no white dot between the color changes before xine player:

picture 2 is from the LVDS output, there are a lot of white dots between the color changes before xine player! 

So it's not the video decoder problem!

Hi George,

Have you probed the power rails to double check that the power supplies are functioning correctly?

Best,

Nikolas

We are building a level shifter to try.

Regards,

George

Hello George,

Okay. Please let me know when you have any updates.

Best,

Nikolas

Can we use SN65LVDT100DR(SOIC) for the level shift ?

Hi George,

This device is not part of the FPD-Link portfolio and is therefore outside of my expertise. I would suggest posting a new E2E thread regarding this particular part (SN65LVDT100DR) for more assistance on constructing your level shifter

With that being said, though, are you not able to directly probe the power rails?

Best,

Nikolas

The power rails are OK, but the problem exists even with the level shift circuit using (SN65LVDT100DR)!

Hi George,

Could you please provide the schematic for the SN75LVDS82?

Best,

Nikolas

rec-7562_v10.pdf

attached is SN75LVDS82 schematic

Hi Jack,

Let's take a step back and try and isolate to pinpoint which component in the system is causing the abnormality. It looks like the i.mx8mplus is capable of outputting both HDMI and LVDS. Could you please disconnect the SN75LVDS82 and instead connect the LVDS output of the i.mx8mplus to the display (i.mx8mplus --LVDS--> display) and see if the white dots persist? This will help identify if the issue lies with the SN75LVDS82, i.mx8mplus, or the display.

As an aside, could you please provide a full block diagram of the system, including what specifically is being output to the "xine player?"

Best,

Nikolas

Hi Nikolas,

Excuse me! without SN75LVDS82 (LVDS receiver), how can you connect the LVDS output of i.mx8mplus to the TFT panel (it's 666 RGB interface)? 

This LVDS receiver circuit works with AMD LX800 with SN75LVDS83 (LVDS transmitter) for our old product (with the same TFT panel) for 16 years already!  

xine player is the AP to play video for Linux system.

Regards,

George

Hi George,

I think this emphasizes the need for a block diagram - I am not familiar with what components are at play in the system design is here. This was the first mention of a TTL (RGB666) panel in this thread, for example. Below is what I've gathered from the thread thus far - can you confirm that this is accurate, including with respect to where video data types are coming and going? 

If this is in fact accurate, then I'd like to revisit these images from earlier in the thread:

Given this information and proposed block diagram above, am I correct that in assuming that both picture 1 and picture 2 being "before xine player" means they are being fed to a display prior to the SN75LVDS82 component, as seen below to display 2, with the white dots being seen when following the green arrow, but not being seen when following the purple arrow?

If this is not accurate, please update the block diagram and let me know where the "HDMI output" and "LVDS output," both before the xine player, referred to in the previous responses are coming from and where they are going to.

Best,

Nikolas

Nikolas,

It should be:

Regards,

George

Hi George,

Thank you for providing the updated block diagram. Please allow me 1-2 business days to discuss this further with my team.

Best,

Nikolas

Hi Nikolas,

Because the previous generation used AMD LX800 (EOL soon), diagram as below, the panel was RGB 565, so that the LSB R0, R1, R2, G0, G1, B0, B1, B2 are all unconnected (which works fine for 16 years).  The panel now used is RGB 666, so that R2 and B2 are connected using 0 ohm resistors.

Regards,

George

Hi George,

What datatype is the i.mx8plus outputting (i.e. RGB666, RGB888, etc.)?

Best,

Nikolas

Hi Nikolas,

 jeida24 RGB888

Regards,

George

Hi George,

The panel is expecting RGB666, correct? Looking at the schematic labelled "rec-7562_v10" in this thread, it looks like the panel has two inputs (R2 and B2) are grounded via two 0-Ohm resistors. Can you confirm if R41 and R42 are populated or depopulated?

Best,

Nikolas

Because the previous generation used AMD LX800 (EOL soon), diagram as below, the panel was RGB 565, so that the LSB R0, R1, R2, G0, G1, B0, B1, B2 are all unconnected (which works fine for 16 years).  The panel now used is RGB 666, so that R2 and B2 are connected (0 ohm resistors R43 and R44 are populated, R41 and R42 are unpopulated)

Regards,

George

Hi George,

Thank you for the additional update. Two follow-up questions:

• What is your PCLK? The SN75LVDS82 has a minimum PCLK of 31MHz, but looking at the display specifications, it supports a maximum PCLK of 27.69MHz.
• Since the schematic is already configured in such a manner that can be adjusted between RGB565 and RGB666, are you able to reconfigure the devices such that the panel is receiving RGB565 and then see if the issue persists? To do so, you would need to depopulate R43 and R44 and populate R41 and R42.

Best,

Nikolas

Hi Nikolas,

1. DCLK  is 25.77MHz from SN75LVDS82 pin 26

2. We managed to solve this problem by setting the output clock from i.mx8mplus to 25MHz. 

We didn't notice that before although we set it up as 25MHz but it automatically changed to 75MHz after booting.  So that we changed the timing of the driver to fix at 25MHz.

Problem solved, thanks

Regards,

George