[time-nuts] have 10MHz need 19.5Mhz

Attila Kinali attila at kinali.ch
Sun Jun 2 19:38:08 UTC 2013


On Sun, 2 Jun 2013 11:59:09 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> Is there a smarter and more direct way to get 19.5MHz for 10MHz?

Are there any documents on the PLL and clock network of the RPI processor?
If so, i would assume that you should be able to switch the input frequency
to 20MHz and then fix the PLL settings in the chip. I wouldnt be surprised
if the 19.5MHz happend because they were cheap and had nothing to do
with the internal frequencies.

As or a different approach: How about using an FPGA? The internal PLL/DLL
allows you to upconvert the 10MHz to anything you want, and you can build an
internal clock generator quite easily. The jitter requirements of modern uC
aren't as high as they used to be, as the clock frequency is upconverted
using an internal PLL to something different. And the PLL/VCO combo filters
out quite a bit of the jitter from the oscillator outside.


			Attila Kinali

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
		-- unknown



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