abuse at cabal.org.uk
Thu Jul 14 08:24:53 CDT 2016
On Thu, Jul 14, 2016 at 12:44:19AM -0500, Sam O'nella wrote:
> I haven't built or marketed anything myself but i believe if i understood
> correctly from several folks who have that vga was a cheaper choice due to
> licensing costs for dvi or hdmi at the time.
Parts of DVI are patented, but there are royalty-free licences available. It's
also fairly like that the patents have all bit expired, or are invalid. HDMI
can be treated as DVI with a different plug.
I doubt supporting either interface would be a problem on licensing grounds. If
nothing else, these things aren't made in high enough volume to attract the
attention of the attack lawyers.
> Not sure if vga is past that point or open but when keeping home brew kits
> cheap for us hobbyists every dollar counts.
This is the more likely reason: DVI and related standards use TMDS signalling
which requires a reasonably complex logic block running at a minimum of 250MHz
to scramble and multiplex the 24 bit RGB into the four output signals. This is
not impossible on low-end FPGAs, but it does eat enough LEs that the designer
may decide to just support VGA rather than cut back functionality elsewhere or
require a more expensive FPGA.
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