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TMDS171: Automatic redriver to retimer mode - How it works?

stefano vaghi
Prodigy 75 points

Part Number: TMDS171

Hi

we have experienced a problem with the TMDS171.

We are using a video source which can be either with a 110MHz Pixel Clock or 140MHz Pixel Clock.

The TMDS171 on the display side is configured in "Automatic redriver to retimer mode".

In production we have found that even if on many units the display is working correctly, on some unit the display visualize a black image or an intermittent image/black image.

Analyzing the problem, the root cause was the TMDS171.

Changing the configuration of the TMDS171 to "retimer mode", solve the problem.

In your datasheet it is described that "The retimer is automatically activated at pixel clock above approximately 100 MHz" and that "At pixel clock below about 100 MHz, the TMDS171 automatically bypasses the internal retimer, and operates as a redriver." so, why in our case with a 110MHz or 140MHz pixel clock the device is not working in retimer mode??

Please clarify if we have not understood the modes of operation.

If we plan to use always the "retimer mode", what happens if the video source has a Pixel Clock that is <100MHz? Is it a valid operation mode or should we expect problems?

Thanks

Best Regards

Stefano

  • 0
    TI__Guru**** 187281 points

    Stefano

    The TMDS171 retimer is automatically activated at pixel clock approximately above 100 MHz when TMDS171 is being configured for automatic Redriver to Retimer Cross Over at 1.0 Gbps.

    When the device is set to 11 - retimer only mode, it will stay in retimer, and not enter redriver mode at any resolution.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 75 points

    This is what I have read on the datasheet, but it is not clear in two points:

    1)If we plan to use always the "retimer mode", what happens if the video source has a Pixel Clock that is <100MHz? Is it a valid operation mode or should we expect problems?

    2)With a Pixel clock of 110MHz or 140MHz in "Automatic redriver to retimer mode" we have problem in the video received. The device should work in "retimer mode" as said by the datasheet with this Pixel clock frequencies.  If i change the mode to "retimer mode" the video has no problem anymore so I assume that the device when it was configured in "Automatic redriver to retimer mode" it was not working in "retimer mode". This is not expected from the behavior written in the datasheet. Can you explain?

  • 0 in reply to stefano vaghi
    TI__Guru**** 187281 points

    Stefano

    1) You can set the device to all redriver mode or all retimer mode with no functional impact, but retimer performance is better at 1080P or greater resolutions.

    2) Would you please dump out both Page 0 and Page 1 register for the case when TMDS171 is being configured as "Automatic redriver to retimer mode" and the case when TMDS171 is being configured as "Retimer mode" only so I can analysis the issue?

    Thanks

    David