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Altera_Forum's avatar
Altera_Forum
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16 years ago

VGA 25MHz, Clock 100MHz, Help!

Hi, I would like to use a 100MHz clock to drive my logic, but the problem is that VGA needs a clock of 25MHz. Right now, I am using 2 PLLs to create a 100MHz clock and 25MHz clock by us...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

a VGA controller is realy a pretty simple statemachine, just some counters and a bit combinatorial logic thats it.

you need a counter for x and one for y

based on these values you generate the blanking signals

i could give you an example for 640x480 und you just need to add 2 bit counter to slow down the pixel rate from 100 : 25 = 4 : 1.

vga runs at 25 very well

if you just add your own vga controller and let it run at 100MHz you wont need to worry about the clock crossing stuff