AT91SAM7S128 and USB crystal frequency

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I am confused on which crystal to use. The AT91SAM7S128 can go a max of 55MHz, and for my app, higher the better. However, the manual is confusing me about what I'm limited to using for the USB:

page 26:
"Communication through the USB Device Port is limited to an 18.432 MHz crystal."

on page 146:
"A 48 MHz USB clock is necessary to use the USB Device port. It has been programmed ear-
lier in the device initialization procedure with PLLB configuration."

page 190:
"The USB Source Clock is the PLL output. If using the USB, the user must program the PLL to
generate a 48 MHz, a 96 MHz or a 192 MHz signal with an accuracy of ± 0.25% depending on
the USBDIV bit in CKGR_PLLR."

http://www.atmel.com/dyn/product...

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Hello,
if you want to use the boot assistant you have to provide a 18.432MHz crystal. That's what page 26 wants to tell you.
Using USB requires a 48MHz clock always. To get it from the 18.432MHz crystal the PLL is used with div by 48 and mul by 125.
To handle all requirements of the PLL like the lowest frequency of 1MHz you can't div by 48. You can div by 12 only which gives you 192MHz of PLL but the USB has a div by 4 to get its 48MHz.
Over all if you want to use USB your max CPU clock will be 48MHz too. If you want to use the boot assistant your crystal must be 18.432MHz.

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Ok, that was a bit confusing . . .

So I use a 18.432MHz crystal, but my CPU would still be 48MHz somehow by using div by 48 and mul by 12?

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