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SN65DP149: SN65DP149 DP to DVI Converter Functional Problem

Eray CANLI
Intellectual 335 points
Part Number: SN65DP149

Hello,

I am working on a DP to DVI converter using SN65DP149 IC. Manufactured the PCB, assembled but it is not functioning.

I am using pin strapping for configuring the converter as follows:

I2C_EN/PIN is low, pin strap mode

EQ_SEL/A0 pin is floating. adaptive EQ

SLEW_CTL pin is high, fastest data rate

PRE_SEL pin is floating, 0dB

HDMI_SEL/A1 pin is high, configured for DVI

DP connector is about 5 cm from IC (on flex part of the converter), DVI connector is over a 40cm cable. Differential pairs are twisted.

When measured pins, OE pin is about 2.5V. When connected to the source and monitor, HPD_SNK pin is 5V, HPD_SRC is 3.3V, I2C pins are pulled up.

Attaching schematic of my board:

  • 0
    TI__Mastermind 23815 points

    Hi Eray,

    DP149 is a passive converter or level shifter from DP++ to HDMI/DVI. This is not an active converter from DP to HDMI/DVI.

    The passive converter takes HDMI/DVI video AC-coupled(This is DP++) at the input and sends HDMI/DVI video DC-coupled at the output.

    To tell the GPU to send HDMI/DVI video you need to assert CAD(CONFIG1) signal, currently, you have it tied to GND.


    Long story short

    Make sure GPU is DP++ capable

    On DP connector assert CONFIG1(CAD) high

    Finally is better to use snoop mode on SCL_SNK/SDA_SNK, in case GPU or displays don't support I2C clock stretching, I will send you reference design by email.

    Regards

  • 0 in reply to Moises Garcia
    Intellectual 335 points
    Dear Garcia,

    Thanks for your reply.

    My final setup will be a DP++ output, but currently trying my converter on an 'Nvidia Quadro K620' graphics card, which I am not sure if DP or DP++. Datasheet of this graphic card says DP 1.2 output, but nothing about DP++. Should I assume this is a non-DP++ ?

    I have noticed CONFIG1 (CAD) lately and added a 100K pull-up to 3.3V supply pin of DP connector. When plugged, I measure 800mV on this pin. Couldn't find a minimum level for this pin. Is 800mV OK? Should I use a lower resistor, or directly tie?

    About snoop mode, I don't know what it is yet, but will look and try it.

    Thanks and Regards.
  • 0 in reply to Eray CANLI
    TI__Mastermind 23815 points
    Hi Eray,

    I'm not familiar with this video card, computers DP++ capable have the dual mode symbol printed, however having 800mV is very low in CAD after asserting it high, which makes me think it doesn't support DP++.

    Tying CAD to 3.3V is not recommneded, in some old GPU CONFIG1 is tied to GND, so this woule make a short circuit.
    Check if the current provided by the computer through DP_POWER is enugh to power DP149.

    Regards
  • 0 in reply to Moises Garcia
    Intellectual 335 points
    Seems logical, I think this video adapter is not DP++. There is another PC with DP++ output, I will try on that and share the results. Thanks again!
  • 0 in reply to Moises Garcia
    Intellectual 335 points

    Hi Moises,

    I have tried my board with a DP++ dual-mode source, not working yet. And also, I have observed that Pin 13 of DP connector, which is Cable Adapter Detect, is again around 800mV levels.

    So, I have checked with 'VESA DisplayPort Interoperability Guideline v1.1' and part 5.4 states following:

    I am confused about this, are we pulling high, if so, why is it expecting a voltage under V_IL?

    Thanks!

  • 0 in reply to Eray CANLI
    TI__Mastermind 23815 points

    Hi Eray,

    Document 'VESA DisplayPort Interoperability Guideline v1.1' is the one available on the internet, but in 2009 version 1.1a was released where that "typo" was corrected. In document version 1.1 figure 5-1 you can see there is 1M pull-down on pin 13, and a 100k pull-up on the same pin of adaptor's side.

    Perhaps the GPU is not sensing CAD(Marked as optional in DP++ standard) and is looking for cable adaptor registers, could you configure DP149 for HDMI instead of DVI?

    Could you monitor activity on AUX channel?

    Regards