[Open-graphics] TV out
miller at techsource.com
Thu Dec 2 12:30:51 EST 2004
Rene Herman wrote:
> Timothy Miller wrote:
>> Rene Herman wrote:
>>> Would certainly work, but please do pardon my ignorance -- I don't
>>> understand why it's a problem to have a signal both on the TV-Out and
>>> the VGA Out, if both are exactly the same. Those standard TV-Out
>>> chips do modes at least my monitor(s) don't have a problem with. It's
>>> always worked fine for me...
>> The timing is completely different.
> That's the job of the TV-Out chip, is it not? From the Philips datasheet
> for example:
No. That's the job of the video controller which has a bunch of
counters in it. The TV-out chip does format conversion.
> The SAA7102; SAA7103 can be directly connected to a PC video graphics
> controller with a maximum resolution of 800 x 600 at a 50 or 60 Hz frame
> rate. A programmable scaler scales the computer graphics picture so that
> it will fit into a standard TV screen with an adjustable underscan area.
> Non-interlaced-to-interlaced conversion is optimized with an adjustable
> anti-flicker filter for a flicker-free display at a very high sharpness.
Well, alright, you can have a chip with a framebuffer in it and a scaler
which will take a higher res and reformat it for TV. That wasn't what I
was going for.
> That is, as far as I'm understanding this you just T-split the (in this
> case) 800x600 at 50/60 signal to VGA and TV-Out chip and it does the rest
> as far as TV output is concerned. Wrong?
It just sounds like an expensive chip. I suspect you need a fair amount
of RAM to hold a framebuffer which is being filled with different timing
from how it's being scanned out. Indeed, you need 3X the amount of
space for the final image in order to eliminate tearing in the image.
Our medical cards have to do rotation of images in video output so we
can drive monitors in portrait mode. This is no trivial matter given
that DRAM isn't totally random access (row activate and precharge times
can kill your throughput).
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