Content originally posted in LPCWare by liaochengyi on Tue Dec 16 02:22:24 MST 2014
Dear Paul,
Thank you for the fast reply! :)
I checked the user manual and found the 4.4.5 USB PLL control register
The PLL accepts an input frequency from 10 MHz to 25 MHz from various
clock sources. The input frequency is multiplied up to a high frequency, then divided down
to provide the actual clock 48 MHz clock used by the USB subsystem.
and PSEL just can select: 1, 2, 4, 8
But my external clock option is: 4, 5, 10, 20Mhz
If I need the 48Mhz USB clcok -->
1. Select 20Mhz input, MSEL = 5, --> need PSEL = 12. :((
2. Select 4Mhz input, MSEL = 12, --> PSEL = 0
But I can't use the 4Mhz clock input. Right?