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PCM2705 changing ROM descriptor

Other Parts Discussed in Thread: PCM2705

Hello all, I'm using PCM2705 with SPDIF out and SPI connected to a uC for reprogramming of USB descriptor.
Host pin is connected directly to USB Vbus and D+ pullup is derived from USB Vbus.

It seems that descriptor reprogramming does not take effect before I have plugged and unplugged the USB cable, then send ROM descriptor through SPI and then plug again the USB cable.

If I send ROM descriptor at power up with USB cable already plugged, it show "USB audio DAC".

Should I enable the D+ pullup only after ROM desc reprogramming? The datasheet seems to have not so much detail about it.

Thank you

  • Hi Francesco,

    Welcome to E2E and thank you for your interest in our products!

    The D+ pull up must not be activated until after modifying the descriptors is complete.
    You need to follow the instructions from section "Descriptor Data Modification" of the data sheet.

    Best regards,
    Iván Salazar
    Texas Instruments
  • Hello Ivan,

    thank you very much, I was reading the old revision of the datasheet, and this section is not present.

    Do you think it is possible that TI will develop a new IC to support USB Audio Class 2.0, up and over 192KHz? It could be a huge success.