ATSAMD21 USB Clock requirements...

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Hi guys...I am a little confused with this issue of clock source for USB in Host mode.

I have successfully used DFLL in closed mode with SOF clock recover option for USB in device mode.

I am not wondering about USB in host mode...it seems we are only allowed to use XIN32??? I cant use any other than 32KHz external crystal input?? This input is a SERCOM port...which I hate to loose! What are my options? Not possible to use XIN port and use 32K crystal on that port?

I really would just prefer to use standard 12MHz crystall...

Last Edited: Fri. Feb 3, 2017 - 10:47 AM
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it seems we are only allowed to use XIN32???

 

No there is no such restriction, you just have to achieve 48 MHz ± 0.25%

http://www.atmel.com/Images/Atme...

has this:

GCLK_USB can be generated from one of the following clock sources in USB Embedded host mode.
• DFLL with external crystal/external clock in XOSC32K/XIN
• DPLL with external crystal/external clock in XOSC32K/XIN

/Lars

 

 

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See above...it says XOSC32K....not XOSC?

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XIN is mentioned also. Just read that document.

/Lars

 

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Atmel has tutorial on how to set the clocks for USB

http://www.atmel.com/images/atmel-42352-sam-d21-xpro-usb-host-msc-bootloader_training-manual_an8185.pdf

See page 11 - "2.3 Clock Configuration"

"When all else fails, read the directions"