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Original question:

TDP158: EDID with TDP158

TDP158: Special Mode on 1.4b

Peter Wei
Expert 3030 points
Part Number: TDP158

Hi Team,

My customer is using TDP158 on their notebook project, on source side. And they only need to support HDMI 1.4b. Here is the questions:

1. If they use DDC Snoop mode, the SDA/SCL_SNK was connected to the DDC too, they are asking what is the purpose for connecting these two pins under HDMI 1.4b, for data rate detection?

2. In special mode, the data rate was fixed on 5.4Gbps, they are asking if under HDMI 1.4b, will it has any problem on the signal condition? Any suggestion on special mode under 1.4b?

  • 0
    TI__Guru*** 139405 points

    Hi,

    1. If they use DDC Snoop mode, the SDA/SCL_SNK was connected to the DDC too, they are asking what is the purpose for connecting these two pins under HDMI 1.4b, for data rate detection?

    As part of discovery the source reads the sink E-EDID information to understand the sink’s capabilities. Part of this read is HDMI Forum Vendor Specific Data Block (HF-VSDB) MAX_TMDS_Character_Rate byte to determine the data rate supported. Depending upon the value the source will write to slave address 0xA8 offset 0x20 bit1, TMDS_CLOCK_RATIO_STATUS. The TDP158 snoops the DDC link to determine the TMDS clock ratio status and thus sets its own TMDS_CLOCK_RATIO_STATUS bit accordingly. If a ‘1’ is written by the source the TMDS clock is 1/40 of TMDS bit period. If a ‘0’ is written, then the TMDS clock is 1/10 of TMDS bit period.

    The TDP158 will always default to 1/10 of TMDS bit period unless a ‘1’ is written to address 0xA8 offset 0x20 bit 1 or during a read by the source this bit is set. This helps determine source termination when automatic source termination select is enabled. Otherwise this bit has no other impact on the TDP158

    2. In special mode, the data rate was fixed on 5.4Gbps, they are asking if under HDMI 1.4b, will it has any problem on the signal condition? Any suggestion on special mode under 1.4b?

    More detail is needed on the 5.4G special mode. The 5.4G sounds like a DP, not a HDMI data rate. Are they trying to go from DP to HDMI?


    Thanks

    David