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Honored Contributor I

Trying to interface VGA with Custom CPU on DE2

Hello everyone! 


I'm trying to interface my CPU with the VGA output on the DE2. I've tried searching on my question, but have turned up empty handed. I'd like to apologize a head of time for the long post. 


Anway, here is what I'm trying to do: 


I created a custom CPU want to be able to connect my Data Cache module to the VGA port of the DE2. I'm only using the M4K blocks at this time, so I know that I do not have enough memory to buffer an entire 640x480 res image. However, I was thinking of just cycling through the Data Cache over and over until the entire screen has an image on it. 


My problem is that I've tried several different VGA driver files (one off of the DE2 CD, another off of the Altera website, another from the file that someone else posted on this site, and some other file from somewhere... sorry forgot) but I cannot get a basic white image on the screen (each of the RGB values is set to 10'b1111111111 for white). All I get is a blank black screen. I tried to switch the values to all zeros, and other combinations but I get the same result. I did create a 25.175MHz PLL and connected the VGA file and VGA clock pin to the same clock. I've tried several monitors and each can detect a 640x480 res at 60Hz connection. 


So at this point, I have no idea what to try next? The board can output a video signal just fine (power up demo) so either I'm using the incorrect VGA file or I'm doing something wrong. I ran SignalTap on all of the inputs and outputs to the VGA file and the capture shows the VGA output signals. By the looks of it, I think the VGA driver files are doing what it’s supposed to, based on the timing conditions inside the file, but I’m not too sure. Since I'm not too familiar with the VGA signal generation side of things, I'm not sure where to look for the problem. Does anyone have any suggestions?  


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