11-25-2010 08:23 AM
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
11-25-2010 06:39 PM
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.
11-25-2010 11:25 PM
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
11-26-2010 07:29 AM
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
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.
11-26-2010 11:39 PM
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.