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USB CDC on LPC1768 problem

Lukasz Gesieniec

Hi,

I have a problem with running a USB-CDC on the LPC1768. I have a USB circuit identical to the MCB1700 board. I use the sample code for USBCDC MCB1700 board.
My program stops at the following line:
while (! USB_Configuration);
On the computer I get the message: "USB Device not Recognized."
Is it a hardware or rather a software problem? Sorry for my English.

Best Regards,
Lukas

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  • 0 in reply to Lukasz Gesieniec

    The above is limitations for the PLL1 which is a special PLL for the USB.

    It is also possible to take the 48MHz clock from PLL0 (which is also used for processor core and all other peripherials).

    I haven't verified it, but I'm pretty sure that you can run PLL0 with a 10MHz crystal and get your 48MHz USB clock with zero error. After all, 10 * 24 / 5 = 48MHz so there are small integers that you may multiply/divide with to get the required frequency. PLL1 is more limited than PLL0, so it doesn't have the same flexibility.

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  • 0 in reply to Lukasz Gesieniec

    The above is limitations for the PLL1 which is a special PLL for the USB.

    It is also possible to take the 48MHz clock from PLL0 (which is also used for processor core and all other peripherials).

    I haven't verified it, but I'm pretty sure that you can run PLL0 with a 10MHz crystal and get your 48MHz USB clock with zero error. After all, 10 * 24 / 5 = 48MHz so there are small integers that you may multiply/divide with to get the required frequency. PLL1 is more limited than PLL0, so it doesn't have the same flexibility.

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