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Altera_Forum
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12 years ago

PLL Megafunction actual clock frequency

Hi, I am using the Altera PLL Megafunction to generate 6 different clocks (100, 125, 200,50, 1MHz) with a reference clock of 100 MHz. I set all the frequencies correctly except for the 1 MHz c...
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Altera_Forum
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12 years ago

Try switching "PLL Mode" to Fractional. In Integer mode, you are stuck with the K divider at 1 in the GUI so VCO minimum of 600MHz feeds the dividers, which each have maximum value 512 so the minimum output is the 1.17MHz you saw.

It will work for your single output of 1.000MHz But with the other clocks added, it looks like 125MHz is going to be the problem.

The PLL is described in:

http://www.altera.com/literature/hb/arria-v/av_52004.pdf

And page 4-27 is probably what you're most interested in while trying to understand what the wizard is producing for you.