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TMDS181: can not support Set-top box output

Jesse Lee
Expert 1985 points
Part Number: TMDS181

hello

1. we use TMDS181 for 15m HDMI Extend cable,  now it can display normally when connecting the cable with computer.

2. But when we connect cable with set-top boxes which have different brands they all have no display on a monitor, PS4 which made by Sony is as well as set-top box.

  After using 1m of length's cable, the issue also exists.

Is there any difference of HDMI output format for computer and set-top box?

thanks a lot.

 

  • 0
    TI__Guru**** 177211 points
    Jesse

    Are you using the EVM or your own design? If it is your own design, would you please share your schematic?

    Can you also dump out TMDS181 register between the computer and PS4?

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    Expert 1985 points

    1. we are using our own PCBA, Pleae refer to attachment for schamatic.01 Main.pdf

    2. Can you also dump out TMDS181 register between the computer and PS4?

    For this question,  do you mean if we can read out the TMDS181 registers and compare their values?

  • 0 in reply to Jesse Lee
    TI__Guru**** 177211 points

    Jesse

    1. HPD_SRC is a 3.3V output, you need an external level shift circuit to shift the voltage from 3.3V to 5V. Please refer to Figure 35 of the datasheet.
    2. Because not all source supporting clock stretching, we recommend not to use the active DDC block inside TMDS181, but use DDC snoop instead. For DDC snoop, the SDA/SCL from the source is connected directly to the SDA/SCL sink. The TMDS181 will need its SDA_SNK and SCL_SNK pins connected to this link in order to correctly configure the TMDS_CLOCK_RATIO_STATUS bit. Care must be taken when this configuration is being implemented as the voltage levels for DDC between the source and sink may be different, 3.3 V vs 5 V. SDA_SRC and SCL_SRC must be pulled to GND. You may also need to consider adding an external I2C buffer for DDC capacitance isolation.
    3. Is I2C_EN high or low?
    4. Do you have pullup on SCL_CTL and SDA_CTL?
    5. How do you connect SIG_EN?
    6. Consider changing the pullup on SDA_SNK and SCL_SNK to 47k.

    Thanks
    David

  • 0 in reply to David (ASIC) Liu
    Expert 1985 points
    Hi David
    Now our customer re-edit the circuit:
    1. about HPD setting, use snoop mode which copy from the figure 36 in datasheet : pin 4 is float, use 1KΩ resistor to pull up with 5V;
    My questions :
    Is it necessary to add external level shift circuit when not using HPD snoop mode ?
    If the source side's requirement is 3.3V, and can we add 5V external level shift circuit ?
    Is the external level shift circuit only used for 5V HDMI source ?


    2. About DDC setting, use DDC snoop mode which copy from the figure 36 in datasheet.
    3. I2C_EN is high
    4. No, both SCL_TCL and SDA_CTl are float
    5. SIG_EN is float
    6. SDA_SNK and SCL_SNK's pull up resistors' value are 47K

    But now all computers, set-top boxes and PS4 can not display on any monitors.
  • 0 in reply to Jesse Lee
    TI__Guru**** 177211 points
    Jesse

    For I2C_EN, Pre_SEL, EQ_SEL, pullup/pulldown resistors need to be 65k.
    SCL/SDA_CTL need to be pulled up to 3.3V through 2k resistor.
    SIG_EN needs to be tied low.

    HPD_SNK max VIL is 0.8V, and min VIH is 2.1V, so level shifter is not needed. Level shifter is needed if the source is 5V.

    Do they have I2C_EN pulled high or low? The schematic shows I2C_EN is low. If I2C_EN is high, then TMDS181 register, particularly the TX_TERM_CTL needs to be set correctly depending on whether the source is HDMI1.4 or 2.0.

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    Expert 1985 points
    Hi David
    In TMDS181‘s datasheet, we can not find the application circuit for actvie cable, only have the simplified diagram, Figure 37.
    Could you help provide the full version schematic for the application of active cable using TMDS181？
    Thanks
  • 0 in reply to Jesse Lee
    TI__Guru**** 177211 points
    Jesse

    You can refer to DP159 Figure 32 as a reference for a dongle design.

    Few modification needs to be made:

    1. To avoid source not supporting clock stretching issue, please follow my recommendation on DDC. When connecting DDC directly between the source and the sink, you may need a I2C buffer to isolate DDC capacitance.
    2. You may need a buffer on HPD coming from the sink side to make sure HPD is 0V when sink power is off.

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    Expert 1985 points

    Hi  David

    1. For I2C buffer,  could you heip recommend the device part number?

    2. In DP159 Figure 32,  HPD_SRC directly connect to Source side HPD,  HDP_SNK also directly connect to Sink Side HPD.  

    So should we choose this connecting method?  and must we add the external level shift circuit?  IF the source is 3.3V,  and we add the external level shift circuit, can it work normally? 

    3. For I2C control pins, If we don't use external I2C control function, can we set  I2C_EN to low?   In this situation, whether the TX_TERM_CTL need to set?

    4. can we use TMDS181RGZEVM to demonstrate the active cable application? 

    If yes, how do we to config the setting on the TMDS181RGZEVM board?

    My confusion is :  If the I2C buffer is necessary to avoid source not supporting clock stretching issue, TMDS181RGZEVM can not be used directly to demonstrate?

    5. Maybe TMDS181 is not suitable for the active cable application?

  • 0 in reply to Jesse Lee
    TI__Guru**** 177211 points
    Jesse

    1. Please see this e2e post: e2e.ti.com/.../540657.

    2. There are two possible implementations for HPD: HPD routed around DP159/TMDS181 or HDP routed thru DP159/TMDS181. While HPD_SNK is 5V is tolerant, HPD_SRC is a 3.3V signal. So if you rout thru DP159/TMDS181, and the source requires 5V HPD, then you need the level shifter. If you rout around the DP159/TMDS181, then level shifter is depending on the source/sink HPD capability.

    3. Yes, I2C_EN can be tied low. But I would still tie SDA_CTL and SCL_CTL to 3.3V through 2K resistor.

    4. The default configuration of TMDS181 EVM should work. The EVM has jumpers so DDC is connected from the source to the sink, with TMDS181 DDC_SNK connected to the line.

    Thanks
    David