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DIR9001: Decoding S/PDIF signal from HDMI ARC

Tom Van Eyck
Prodigy 10 points
Part Number: DIR9001

I want to use the DIR9001 to decode the HDMI ARC signal from a HDMI connection. As far as I understand it, that signal is basically a S/PDIF signal with a different amplitude and termination resistance.

The problem is that I do not know how to connect the HEAC+ line to the DIR9001 for single mode transmission. I used the DIR9001 evaluation board as a reference to design the following schematic (thinking it would be similar to a COAX signal), but the TV I connect to seems to only start the ARC transmission when R12 is removed. Why is this, and is there a better way to connect the two together?

  • 0
    TI__Mastermind 23520 points

    Hello,

    The format coming out of HDMI  is not compatible to the DIR device and you need to decode it before sending it to DIT device. It seems you are just level shifting the signal and then sending it to DIR. 

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 10 points

    As I said, the format of HDMI ARC is based on IEC 60958-1, which should be able to be decoded by the DIR9001. I have also proven this, because once the TV starts transmitting ARC (after removing R12) I get a valid I2S output from the DIR9001.

    My question is regarding the specific components between the HDMI connector and the DIR9001, because I do not understand how exactly it is supposed to work.

  • 0 in reply to Tom Van Eyck
    TI__Mastermind 23520 points

    Tom, In our  regular applications, the signal  coming to DIR is already  compatible to DIR and we deal with whatever happens inside the DIR. So if signal is not decoded correctly, then DIR can not process it. Having said that, you confirmed  signal coming off of HDMI is already IEC 60958 compatible.  However the signal from HDMI in the  schematic is going to an AC coupling cap but right before that you have a  low value resistor to ground which is pulling the signal low anyway.I think this resistor is to discharge the cap ,but  its value is too low and would interfere with signal going through the 01u cap.

     If you need to level shift  and invert the HDMI signal to 3.3V using the SN74LVC IC, then just send the output of one inverter to  to DIR. If you do not want to go through inversion, then in the schematic, you can remove the connection from voltage divider to input of second inverter, so you simply go through two inversions. 

    Regards,

    Arash