Good Composite->VGA converters for classic computers (& video

Eric J Korpela korpela at ssl.berkeley.edu
Wed Jun 4 18:19:04 CDT 2008


>   Err, what is a 'CGA Interface' if not a TTL-level RGBI one?

>  Don't know, but remember how the 5153 has special circuitry that turns color index #6 brown?

Most of what are currently called "CGA->VGA" converters are analog RGB
input at CGA/NTSC frequencies to (scan converted) analog RGB output at
VGA frequencies.  Which is a good thing because they are build for the
(much larger) classic video game market so they are more veratile than
a strict CGA->VGA converter would be.

S\o you need a small circuit to mix I with the RGB to get an a 3 level
(0,0.5,1) signal that these boards can understand.  You could easily
add a "yellow->brown" converter to this circuit by pulling down the
appropriate lines in a resistor divider when color #6 shows up.  It
would add 1 chip and two resistors to the design (off the top of my
head).

Eric


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