• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 32 subscribers
  • Views 822 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMDS181 Active DDC Block

Jack MacDougall41
Prodigy 10 points
Other Parts Discussed in Thread: TMDS181

Hello there,

I'm looking to get clarification on the advantages/disadvantages of using the following two DDC methods (for an active HDMI cable booster)...

A) TMDS181's full Active DDC block (DDC lines into the TMDS181 via SDA_SRC/SCL_SRC ..then out of TMDS181 through SDA_SNK/SCL_SNK) 

vs.

B) DDC Snoop only mode (DDC lines in bypass only tapping into the TMDS181's SCL_SNK & SDA_SNK pins while the SCL_SRC & SDA_SRC are grounded).

I've tried both hardware implementations as outlined in the datasheet, and both work fine...but what I need is a recommendation for maximizing compatibility in the field long term.

- Which mode would maximize successful interop between HDMI source/sink devices? (even if theoretically)

- Are both options capable of allowing proper Snoop function needed to update the TMDS_CLOCK_RATIO_STATUS bit?  (for HDMI 2.0a usage)

I guess I’m trying to understand why TI seems to lean towards the DDC Snoop-only mode over it's own Active DDC block.  

thanks,

Jack

ake a difference either way...although the customer mentioned that HDMI sources and sinks with different Vol/Voh could be correctly level shifted by TMDS181...improving interop (in theory).  My question, 

  • 0
    TI__Mastermind 23815 points
    Hi Jack,

    TMDS181 impements I2C clock stretching on DDC block, some HDMI source/sink have problems with clock stretching which lead to interoperability problems, that is the reason to use snoop mode instead of the active DDC block. Both methods monitor TMDS_CLOCK_RATIO_STATUS bit.

    Some cables have enough losses on DDC that you need a buffer(DDC active block), if the cable has fixed length and snoop mode works fine, then this mode would maximize successful interop between HDMI source/sink devices.

    Regards