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Adventurer
Adventurer
5,231 Views
Registered: ‎10-26-2010

vga interface for virtex 2 pro30

Dear all

I have now virtex 2 pro30 kit and have an image (gray scale) and i stored it in block ram. the kit contain DAC 8bit for red, green, blue.
my problem is how i can display this image(only 8bit) in this case or how i can send data(image => 8bit) to DAC interface which have 24 pin or bit -8bit for each color.
is there any reference code available which can help me ?

 

 

realy wait your reply for this problem
regards

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Professor
Professor
5,221 Views
Registered: ‎08-14-2007

If you give the same value to all three colors, the output will appear in gray-scale.  So your

8-bit gray-scale data can just be copied to all thre R, G, B ports of the DAC.  VGA timing

will be the same whether the image is color or monochrome.  I'm not familiar with your

kit, so I don't know how it handles the sync signals.  Normally analog VGA uses a 15-pin

D-Sub connector and has separate horizontal and vertical sync signals in addition to

the three analog RGB video signals.  However some interfaces place the sync on the

green video, which would require you to account for them when sending the video

signal to the DAC.

 

HTH,

Gabor

-- Gabor
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Adventurer
Adventurer
5,215 Views
Registered: ‎10-26-2010

hi

 

thanks for reply

also i need to some explanation

as i mentioned before i have virtex 2 pro 30 which include DAC converter (FMS3818 - Triple Video D/A Converter) this DAC include 8 pin for r, g, b signal color and (hsync ,vsync) and clock and (sync, blank).

what is importance of the  (sync, blank) signal? and what is the best time to use them in VHDL code ?

 for color signal is it depend on pixel clock or not ?

 

wait your reply for importance

regards

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Professor
Professor
5,197 Views
Registered: ‎08-14-2007

VGA sync and blanking is very similar to television video standards like NTSC (525/60) and PAL (625/50).

Video lines are sent in a raster from top left to bottom right.  The sync signals define when the horizontal

and vertial "retrace" occurs.  In a CRT this would be when the beam is deflected back to the left or top

of the screen.  Blanking at the start of the line (right after the sync) is called the "back porch" and blanking

after the line (right before the sync) is called the "front porch".  There are also a few lines of blanking

before and after vertical sync.  Usually the blanking after the sync is longer to allow more time for

retrace.  The blanking prevents you from seeing the retrace (those somewhat diagonal lines you

would see on old TV sets if you turned the brightness way up), and it defines the rectangle of

active video.

 

For VGA, normally the horizontal and vertical sync signals are separate, but if you need to use

"sync on green" then the DAC will use the (composite) sync signal to create a negative-going

pulse on the green output.  The DAC blanking input can either set the output level to black

(i.e. the same as feeding zeroes to the R, G, B inputs) or it can make the output slightly

more negative (blacker) than black.  When your target is an LCD or similar digital monitor,

this doesn't really matter because you don't have the retrace issue.

 

Another thing to consider is that the DAC itself often has some number of pipeline stages,

and if you use the separate sync signals, their timing relative to the analog video will be

off by the pipeline delays of the DAC.  For most modern monitors this shift of a handful

of pixel times usually doesn't matter, but if you want to comply with the VESA standards

you should probably delay the sync accordingly.

 

HTH,

Gabor

-- Gabor
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Adventurer
Adventurer
5,185 Views
Registered: ‎10-26-2010

hi

 

Thanks for reply

I need to know . when do I need to use sync on green signal?

And what is the importance of this signal? In brief

regards

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Mentor
Mentor
5,174 Views
Registered: ‎11-29-2007

hodahussein,

 

why don't you have a look at the board's documentation and reference design? I guess you have the XUPV2P board? You can find the reference designs here and the documentation here. You should also look at the datasheet of the FMS3818, which a simple Google search will find for you. Together with Gabor's excellent explanation, you should be able to figure out how to make your VGA output work.

 

 

Adrian



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