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Valued Contributor III
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VGA display mode

hi: 

in the DE2 demo,there is a "VGA_Param.h" file ,in this file,pixel display frequency is 25MHz,I want to replace it of 50MHz,so I think the Horizontal Parameter and Virtical Parameter should be multiplied by 2,for example H_SYNC_CYC is 96,so if pixel frequency is 50MHz,H_SYNC_CYC is 96 

*2,but I cannot get any image in VGA,it says the "the output pixels is too much to display". 

so ,if I want to use 50MHz,how to resolve the problem?
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Valued Contributor III
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Re: VGA display mode

hi, 

 

I don't have this board but vga timings are definined in VESA specifications : 

http://martin.hinner.info/vga/timing.html 

or 

http://www.epanorama.net/documents/pc/vga_timing.html 

 

choose the timings which correspond to your resolution/pixel frequency.
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Valued Contributor III
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Re: VGA display mode

The video clock is horizontal * vertical * frame rate. If you double both the horizontal and the vertical, the clock rate would actually increase by a factor of 4.

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Valued Contributor III
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Re: VGA display mode

kevin,thanks for your reply~ 

in 25MHz mode,the parameters are as follows: 

format horizontal parameters vertical parameters 

640*480,60Hz, 640 16 96 48 480 11 2 31 

 

then in 50MHz mode,the parameters are replaced by : 

format horizontal parameters vertical parameters 

1280*480,60Hz, 1280 32 192 96 480 11 2 31 

 

but I also get the message from VGA says"the ouput data is too much to display",then I change those parameters according to the webhttp://martin.hinner.info/vga/timing.html (http://martin.hinner.info/vga/timing.html

 

format horizontal parameters vertical parameters 

800*600,72Hz, 800 56 120 64 600 37 6 23 

 

in 25MHz mode,I can get nice image,but when I try to change the pixel frequency to 50MHz, I cannot get any image,there is always "ouput data is too much to display" in the VGA display screen~ 

 

 

I have think about the VGA display mode for serveral days,but I also cannot get any meaningful conclusion~
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Valued Contributor III
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Re: VGA display mode

- check that your screen supports your video parameter : frame rate and resolution 

 

- check the width of every counter in your code. you need higher maximal values, maybe some counters can't reach these values.
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Valued Contributor III
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Re: VGA display mode

SebastienG,thanks~ 

 

now,I can get image in the VGA,I donnot understand why ,but it can display , so I am very happy! 

but the time of X_START 

("X_START = H_SYNC_CYC+H_SYNC_BACK" )seems not enough,it eats my active image,when I add it to" H_SYNC_CYC+H_SYNC_BACK+120",then I get a unwounded image,I think maybe my screen does not support my video parameters,so I want to ask the reasons here!~
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Valued Contributor III
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Re: VGA display mode

I think you have to check which video format are supported by your screen (try to find the datasheet). 

 

The screen detects sync signals to identify video format. If data are not well synchronized with sync signals the image isn't well displayed. You can simulate your design to verify timings, data...
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