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Original question:

TDP142: TDP142 application on a docking system

TDP142: difference between aux snoop enable and disable in GPIO mode

Jerry Chen
Expert 5110 points
Part Number: TDP142

Hi team,

In GPIO mode, what is the difference between aux snoop enable and disable? I didn't see a clear description in datasheet. 

Thanks.

  • 0
    TI__Guru**** 176631 points

    Hi,

    The TDP142 AUX Snoop function monitors the native AUX traffic as it traverses between DisplayPort source and DisplayPort sink. For the purposes of reducing power, the TDP142 manages the number of active DisplayPort lanes based on the content of the AUX transactions. The TDP142 snoops native AUX writes to DisplayPort sink’s DPCD registers 0x00101 (LANE_COUNT_SET) and 0x00600 (SET_POWER_STATE). TDP142 disables/enables lanes based on value written to LANE_COUNT_SET. The TDP142 disables all lanes when SET_POWER_STATE is in the D3. Otherwise active lanes will be based on value of LANE_COUNT_SET.

    So the difference between AUX Snoop enable and disable is in the power consumption when TDP142 is in 2 lane or 1 lane mode.

    Snoop mode enable -> reduction in power consumption as the unused lane automatically turns off

    Snoop mode enable -> no reduction in power consumption as all four lanes are automatically enabled 

    Thanks

    David

  • 0
    TI__Guru 64326 points

    Hi Jerry,

    See below excerpt from section 8.3.1 Displayport in the TDP142 datasheet.

    "When TDP142 is enabled for GPIO mode (I2C_EN = "0"), the SNOOPENZ pin can be used to disable AUX snooping. When SNOOPENZ pin is high, the AUX snooping functionality is disabled and all four DisplayPort lanes will be active."

  • 0 in reply to David (ASIC) Liu
    TI__Expert 5110 points

    Hi David,

    If I disable snoop function in GPIO mode, could I leave AUXn&p unconnected?

    Thanks.

  • 0 in reply to Jerry Chen
    TI__Guru**** 176631 points

    Hi,

    For unused AUX pin, the AUXN pin should be pulled up to 3.3V through 100Kresistor and the AUXP pin should be pulled down to GND through a 100K resistor.

    Thanks

    David