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USB interrupts also when no cable is connected!

Tamir Michael

Hello,

I am not the world's biggest USB expert, thus I am a little puzzled about the LPC2478 needing to handle USB interrupts regularly even when not connected to a host (without the USB cable connected, even). I am running a CDC connection. Is there a good explanation for this or do I need to disable the ISR until I see USB Vcc appearing?

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    > the LPC2478 needing to handle USB interrupts regularly even when not connected to a host

    Usually, you don't see any USB interrupt while disconnection.
    It may be caused by noise on the D+/D- pins.

    For self-powered device,

    - Disable USB engine while disconnection (PCUSB bit of PCONP). Initialize it after the detection of VBUS voltage

    OR

    - Attach extra pull-ups (100k or more) to the D+ and D- pins, if the USB engine is kept alive.

    Tsuneo

Reply
  • 0

    > the LPC2478 needing to handle USB interrupts regularly even when not connected to a host

    Usually, you don't see any USB interrupt while disconnection.
    It may be caused by noise on the D+/D- pins.

    For self-powered device,

    - Disable USB engine while disconnection (PCUSB bit of PCONP). Initialize it after the detection of VBUS voltage

    OR

    - Attach extra pull-ups (100k or more) to the D+ and D- pins, if the USB engine is kept alive.

    Tsuneo

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