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ST32F407 "HSI as USB CDC" or "Separating SYCLK from USBCLK"

Question asked by h..marc on May 29, 2013
Latest reply on May 30, 2013 by h..marc
Hello,
we want to implement a pulse generator with Timer1, clocked by SYCLK. For marketing reasons we'd prefer a granularity of 10ns, therefor we'd set SYSCLOCK to 100MHz.
At the same time we'll need a USB CDC for our user interface (FS-interface, device only).
Crosschecking the HSI-spec (factory accuracy -8..4,5%) and the USB2 spec, should rule out using HSI as USB clock.
On the other hand, we're pretty sure that the DFU-bootloader runs from HSI.

So - does anybody have experiences with using HSI as USB clock?
Or - even better - any suggestions for both basing 100MHz-SYSCLOCK and 48MHz-USBCLOCK on a crystal?

Looking forward your ideas,
 marc
 

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