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Altera_Forum's avatar
Altera_Forum
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16 years ago

Cyclone III PLL VCO Granularity

Hi all, I would like to reconfig the PLL to different frequencies given by a string. I use a PIC for that and kind of a brute froce method. To calculate the error i need to know the PLL interna...
Altera_Forum's avatar
Altera_Forum
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16 years ago

Regarding 599 mhz, I believe you answered your own question, but I will just state it another way. If the VCO freq is outside 600-1300mhz, then mega wizard will adjust the settings so the VCO is within its operation range. So if you have a 12Mhz input, the minimum frequency multiplier that can be used is 50 otherwise you would have no chance to hit 600mhz vco requirement. Then PLL can divide the VCO by k.

f= (12*(m/n))/k

You can use the mega wizard to recommend settings, and then dump the values to a ROM file in the wizard. The ROM files have parameter settings which you can use to reconfig the PLL.

I believe m & n are 8 bits and k is 16 bits.