[En-Nut-Discussion] SAM7X using 20Mhz rather than 18.432Mhz

[Rick Collins]

At 06:58 AM 9/19/2006, you wrote:
>I am designing a board at the moment using the SAM7X256 and intending to 
>run ethernut. I have no use for USB so I am not tied to 18.432Mhz. How 
>difficult is it to alter the ethernut for a different frequency, I already 
>have 20Mhz, I want the uarts to still have correct baud rate, timers to 
>work processor PLL be set up ect. Can anyone give a hint at where to look 
>in the code?


David,

I have worked with the SAM7S parts and I believe they have similar 
clocking.  On the SAM7S changing the crystal is matter of changing the PLL 
parameters which may require a change to the external RC PLL filter.  There 
is a program (excel spreadsheet) that will help you figure out how to 
program all this and gives you info on the filter "damping factor", 
IIRC.  Atmel makes available somewhere on one of their two web sites.  I 
don't recall exactly where the file is, but if you go to AT91.com and nose 
around in the forums you can likely find a link to it.  Or ask your Atmel 
FAE.  Their web sites are pretty much crap when you want to find something 
other than a data sheet.  I work for a company that gets good support 
because of the quantities they buy.  Otherwise it would be a PITA to get 
anything working from Atmel.

Oh, I almost forgot.  I may have posted about this program to the Yahoo 
AT91SAM group.  Search there for PLL and see what you find.  It would have 
been about two months ago I think.