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Altera_Forum
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18 years ago

Cyclone III - PLL VCO range ?

Hello, What is the frequency range of CycloneIII PLL VCO ? PDF writes 600-1300MHz, but altpll withard creates PLLs with frequencies less than 350MHz. For PLL reconfiguration feature it's ...
Altera_Forum's avatar
Altera_Forum
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18 years ago

Hi,

I am betting there is an error in the MegaWizard when it comes to showing the VCO frequency. The Cyclone III device family's PLL has a new counter called the "VCO post scale counter" which divides the VCO frequency by 2. It can also be bypassed.

The MegaWizard seems to report the frequency _after_ the VCO post scale counter as the actual VCO frequency. So, if your details show the VCO post scale counter a value of 2, you would have to multiply the reported VCO frequency by 2. In your screendump the actual VCO frequency would then be 720 MHz..

Rgrds,

pakumpul