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TMDS181: Function error on RX side

Shu-Cheng LIN
Guru 11785 points
Part Number: TMDS181

Hi Sirs,

Sorry to bother you.

We have use TMDS181

We use 4K*2K 60hz signal input from connector, The output is connect to inside FPGA
For now we found Pin11,12 have input CLK, But if add TMDS181 there will no output on Pin25,26.

So out FPGA couldn't catch this CLK. But if remove 181, the FPGA could.

Our EQ/DE setting is on H/W mode control.

Could you help check our schematic and our application (TMDS181 on RX side) is OK?

Thanks for your help.

Schematic as below

  • 0
    TI__Guru 60870 points
    Hi Shu-Cheng,

    If the I2C_EN pin is pulled high, the pin settings of the TMDS181 device are ignored. This means that when changing between HDMI 1.4B and HDMI 2.0 mode, the user must set the tx_term_ctl by the register. Also, what is the purpose of U45? Is this installed?

    I could not follow the routing of the DDC lines, is the TMDS181 snooping these lines? It must be able to see the setting of the SCDC register to know when to change the clock ratio.

    REgards,
    JMMN
  • 0 in reply to JMMN
    TI__Guru 60870 points
    One more note: I would recommend adding the 500k pulldown on spdif_in to reduce power consumption.
  • 0 in reply to JMMN
    Guru 11785 points

    Hi JMMN,

    Thanks for your reply.

    U45 is use for 181 by Pass function which on FPGA public version reference schematic. Also we have tried removed but still have input CLK and didn't have output CLK.

    We will use 4K 60hz HDMI 2.0 but actually for now we only use 1080P 30hz. 181 didn't have output on (CLK DATA 012). It's looks because something wrong then to be disable TMD181 function.
    We will add pull down resistor on SPDIF IN at next version.
    So, did you have any others idea for this phenomenon (no output) ??

  • 0 in reply to Shu-Cheng LIN
    TI__Guru 60870 points
    Hello Shu-Cheng,

    Can you confirm if HPD_SNK (pin 33) is pulled high? The TMDS181 will not function if this pin is low since the device relies on this pin to determine when a powered sink is attached.

    REgards,
    JMMN
  • 0 in reply to JMMN
    Guru 11785 points


    Hi JMMN,

    Yes, we tried HPD_SNK (pin 33) is pulled high already but still have no output.

    I've attache our schematic by PDF. Could you help check again?6201.TMDS181_HDMI_RX1_for_TI.PDF

  • 0 in reply to Shu-Cheng LIN
    TI__Guru 60870 points
    Hi Shu-Cheng,

    I don't see anything obviously wrong in the schematic. I'm assuming you have already confirmed the power and reset functions. Can you access the TMDS181 over the RX1_181_CTL_SDA/SCL lines? The TMDS181 does not need to be in I2C mode to read the registers. If you can access the registers I will send you information on which registers to read over direct email.

    Regards,
    JMMN