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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
USB can not work with 10MHz oscillator. Quote from the user manual: "Choose an oscillator frequency (FOSC). USBCLK (48MHz) must be the whole (non-fractional)multiple of FOSC meaning that the possible values for FOSC are 12 MHz, 16 MHz, and 24 MHz."
Regards, Lukasz
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.