2 Nov
2006
2 Nov
'06
3:47 p.m.
Ethan Dicks wrote:
It shouldn't be hard to use sets of resistors to
make a
simple, if imprecise, DAC to turn 4 digital bits into 16 analog levels
on the 3 color pins (the "I" bit controls intensity of all three
channels simultaneously, such that if your RGBI pattern is 1111 vs
1110, it's white vs gray (I can't remember if "I asserted" means full
intensity or half, but worst case, if you have it backwards, it's not
hard to invert a TTL signal to flip the sense of the "I" bit before it
goes into your "DAC").
Unfortunately such a conversion would get color index #6 wrong (the one
IBM deliberately darkened in the monitor). But you could account for
that with an additional resistor, maybe?
Repeat for Red and Blue. Voila... digital RGB on an
analog VGA
monitor.
...on an analog VGA monitor that scans down to 15.7KHz.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
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