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TMDS181: TMDS181 SIG_EN setting for HDMI CTS

Chiajung Hsu
Intellectual 280 points
Part Number: TMDS181

Hi Sir,

 

We use TMDS181 on HDMI input design and encounter a problem regarding TMDS181 setting. When we use HDMI pattern generator to generate different video format to HDMI receiver though TMDS181, sometimes HDMI receiver stop working when HDMI pattern generator change video format. However, we can fix this issue by changing SIG_EN setting. If we pull up SIG_EN to enable this function, the problem is fixed. However, the datasheet mentioned that “ By disabling the detect circuit, the receiver block is always on, which is needed for certain HDMI CTS test. Could you comment what is side effect in HDMI CTS if we enable SIG_EN function? We are going to produce this product next week. So, we need to make the decision how to set the SIG_EN before 6/25.

  • 0
    TI__Guru 60870 points
    Hello Chiajung,

    The TMDS181 keeps the receiver terminations enabled at all times even when SIG_EN = H. I believe this was a concern for early pre-release silicon when the receiver terminations were disabled during SIG_EN = H which could lead to the TMDS181 failing the TMDS - Termination Voltage test. The TMDS181 should pass CTS with SIG_EN = H.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Intellectual 280 points

    Hi Jmmn,

    We use pin strap mode for now but we want to have the flexibility to change SIG_EN by I2C. Unfortunately TMDS181 only work at either pin strap mode or I2C mode. Thus, I’d like to know some questions.

     

    1. We want to use CPU’s GPIO to set the I2C mode or pin strap mode by I2C_EN but I have no idea when TMDS181 determine working mode. I just guess that TMDS181 determine the working mode or setting of pin strap when power achieve to valid voltage level. Is it correct?
    2. I noticed that TX_TERM_CTL setting is “Automatically selects the impedance” in strap pin mode but I2C mode has no this option. It seems that the setting is fixed. If I want to keep the same feature in I2C mode, how do I do?

  • 0 in reply to Chiajung Hsu
    TI__Mastermind 23815 points
    Hi ChiaJung,

    The I2C/GPIO configuration can be changed at any time, this has do be done carefully since the configuration will be changed between I2C registers and external pins.

    In I2C mode there is no automatic TX_TERM_CTL you have to select it from the data rate. You can monitor the TMDS_CLOCK_RATIO_STATUS register(0x0B[1]) if it is clear don't set Tx termination if it is set, select 75 to 150 ohms.

    Regards
  • 0 in reply to Moises Garcia
    Intellectual 280 points

    Hi Sir,

    Except for I2C_EN, do you mean that we can change other strap pin setting any time in pin strap mode?

  • 0 in reply to Chiajung Hsu
    TI__Mastermind 23815 points
    Hi ChiaJung,

    You can change all pins at any time.
    If I2C_EN=0 you can switch all other pins without any problem.
    If I2C_EN=1 the pins won't have an effect on the device configuration.
    I2C_EN can be changed at any time too, this has to be done carefully because the configuration will change from pins to registers.

    Regards