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Hello,
i'm implementing a reconfigurable PLL using an ALTPLL e ALTPLLRECONFIG megafunction.
I initialize my PLL with an input freq of 50MHz and only c0 output clock with output freq of 100MHz.
I noticed in the Output clock tab this parameters:
MODULUS FOR M COUNTER = 12
MODULUS FOR N COUNTER = 1
POST SCALE COUNTER = 6
HIGH PERIOD COUNT = 3
LOW PERIOD COUNT = 3
MODE = even
now i changed the output freq from 100 to 125MHz
and the new parameters are
MODULUS FOR M COUNTER = 10
MODULUS FOR N COUNTER = 1
POST SCALE COUNTER = 4
HIGH PERIOD COUNT = 2
LOW PERIOD COUNT = 2
MODE = even
Now the question:
if i want to reconfigure my pll on-the-fly for generate an arbitrary frequency wich are the formulas to calculate the above parameters and pass them to the ALTPLLRECONFIG unit?
thanks for the help
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Hi,
Has anyone found any additional info for this? I am having the same problem and would like the formula to calculate M, N and Post Scale (C).
The documentation I found provides the following:
Fref = Fin/N
Fvco = Fin(M/N)
Fout = Fin(M/(N*C))
This info can be found here
http://www.altera.com/support/devices/pll_clock/basics/pll-basics.html I still do not understand how M,N and C are determined.
For example lets say my Fin = 25MHz and I want Fout = 37MHz.
The megawizard determines M=111, N=5 and C=15.
Does anyone know how these calculations were done?
With a constant Fin I would like to reconfigure my PLL to an arbitrary frequency.
Thank you
Honored Contributor
