2 Jun
2008
2 Jun
'08
11:11 a.m.
Eric Smith wrote:
Eric Smith wrote:
Hm... I use the same bit-pattern in composite color on an IBM CGA, and I
see that same behavior, so does that mean IBM CGA is doing the same
thing, or is the card reversing the supplied bit pattern on every
alternate scanline?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
The Apple II horizontal rate is 228.0 times the
color subcarrier
frequency, so that the color phase is the same on every line.
Jim wrote:
Was there a reason for this design decision?
It was done so that the same bit pattern that produces green on one scan
line also produces green on the next scan line, rather than purple. This
is especially important for the low-res graphics mode, but not doing it
would also have made the high-res mode harder to use.