Re: Apple II graphics

[zcaa1122@rpool3.rus.uni-stuttgart.de (Wulf Hofbauer)]

In article <DEREKN.94Jan28140626@vw.ece.cmu.edu>,
Derek B. Noonburg <derekn@vw.ece.cmu.edu> wrote:
>Once upon a time, I saw an article explaining how the Apple II (not
>GS) generates its video output.  I remember it being a rather clever
>hack involving a very small number of simple chips, and I'd really
>like to find that article.  (There was also something that explained
>how to double the number of colors you could display -- this may have
>been in the same article?)
>
>Can anyone give me a pointer to the magazine or book that this
>appeared in?

I'm quite sure it is an article in a Byte of 1977 oder 1978. If I recall it
right, the hardware modification proposal appeared together with an
article named "A Simplified Theory of Video Graphics" by Allen Watson III.
If you have an Apple ][ reference manual available, it is listed in the
bibliography.

Color generation on the Apple ][ is done by generating 1-0 bit patterns.
As the pixel clock is twice the NTSC color carrier frequency, this will
produce a NTSC TV to display colors. The color can be changed by
controlling the phase relation of the 1-0 pixel stream vs. the NTSC
color burst.

Similar color-generating circuitry can be found in simple video test
pattern generators.

- Wulf

P.S.: NTSC = Never The Same Color.

-- 
 ______________________________________________________
|                                                      |
| Wulf Hofbauer | zcaa1122@rpool1.rus.uni-stuttgart.de |
|                                                      |