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Altera_Forum's avatar
Altera_Forum
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15 years ago

pll reconfiguration on cycloneIII

Dear all, My requirement is to have a pll that can be reconfigured on fly to 2 different frequency 100 MHz and 50 MHz. My input clock is 5MHz. I am using 2 ROM having the settings for the 2 fre...
Altera_Forum's avatar
Altera_Forum
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15 years ago

You never said what device, but I would check what the minimum input frequency is. 5MHz is pretty low and I think some deviced don't support that.

One other thing that might be easier. Most devices have an altclkctrl, which is essentially the global driver after the mux. If you instantiate this megafunction, it has a clock mux that let's you select between the outputs of a PLL. So if you get the PLL to work, you would have a single instance driving out a 50MHz and 100MHz, and dynamically switch between them.