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TMDS181: I2C control on wire compatibility issues

WU YISYUAN
Expert 2165 points
Part Number: TMDS181

Hi, I have some question in I2C control.

After the TMDS181 chip is changed to the I2C control, the compatibility of the HDMI OUT for the wire will be deteriorated without changing the register.

The original usable 4K@60Hz wires will have flower screen, flash screen, no signal problem (4K@60Hz signal).

The debug found that changing the 4:3 bit position of 0Bh to 01, 10, and 11 can all be improved.

The specification of this register is shown in the figure below. Is the parameter of TX_TERM_CTL position actually adjusting the impedance of the internal output of TMDS181 chip?

And The description in section 9.2.3.1.2.2 is to write the corresponding value according to the actual HDMI version? Can't match automatically?

thanks.

  • 0
    TI__Guru**** 176231 points
    Yisyuan

    For HDMI1.4 there are two options:

    Data rate < 2Gbps -> No termination

    Data rate > 2Gbps(< 3.4Gbps) -> 150 to 300 ohms differential termination

    For HDMI2.0 there is just one option

    Data rate > 3.4Gbps -> 75 to 150 ohms differential termination

    In Pin strap mode, when TX_TERM_CTL is NC, the termination impedance is automatically selected. But you lose that automatically termination selection ability when you switch to I2C mode and termination has to be set manually through register 0x0Bh bit [4:3].

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    Expert 2165 points

    Hi David,

    That is to say, different data rates need to change the different differential termination of 181 chips through I2C? Is there no adaptive option for I2C control?

    As below, What  is Reserved mean?

    thanks.

  • 0 in reply to WU YISYUAN
    TI__Guru**** 176231 points
    Yisyuan

    This is correct, unfortunately, TX_TERM will not auto switch when in I2C mode.

    Reserved is for TI internal test mode only.

    Thanks
    David