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docs: update hardware notes

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Vince Weaver 2018-04-23 19:46:55 -04:00
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mode7_demo/docs/mode7_demo.tex
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@ -94,11 +94,13 @@ put this one to shame.
\section{The Hardware}
The Apple II was introduced in 1977.
This demo should run on an original system, though I do not
have hardware quite that old to test on.
I like to troll C64 fans by noting this predates the Commodore 64 by
In theory this demo will run on hardware this old, although I do
not have access to a system of that vintage.
I like to troll Commodore fans by noting this predates the Commodore 64 by
five years.
\vspace{1ex}
\noindent
{\bf CPU, RAM and Storage:}
@ -151,12 +153,12 @@ Hardware page flip & Yes \\
\end{tabular}
\end{center}
The hi-res graphics mode was a complex mess of NTSC hacks by Woz.
You got approximately 280x192 resolution, with 6 colors available.
However the colors were from NTSC artifacts and there were limitations
on which colors could be next to each other (in blocks of 3.5 pixels).
There was plenty of fringing on edges, and colors changed depending on
whether they were drawn at odd or even pixels.
The hi-res graphics mode is a complex mess of NTSC hacks by Woz.
You get approximately 280x192 resolution, with 6 colors available.
The colors are NTSC artifacts with limitations
on which colors can be next to each other (in blocks of 3.5 pixels).
There is plenty of fringing on edges, and colors change depending on
whether they are drawn at odd or even locations.
To add to the madness, the framebuffer is interleaved in a complex way,
and pixels are drawn least-significant-bit first (all of this to make
DRAM refresh better and to shave a few 7400 series logic chips from the design).
@ -168,11 +170,12 @@ Optionally 4 lines of text can be shown at the bottom of the
screen instead of graphics.
The lo-res mode is a bit easier to use.
It provides 40x48 blocks (40x40 if the four
lines of text are displayed at the bottom).
It provides 40x48 blocks, reusing the same memory as the 40x24 text mode.
(As with hi-res you can switch to a 40x40 mode with four lines of
text displayed at the bottom).
Fifteen colors are available (there are two greys which are indistinguishable).
Again the addresses are interleaved. Lo-res Page 1 is at \$400
and Page 2 is at \$800.
Again the addresses are interleaved in a non-linear fashion.
Lo-res Page 1 is at \$400 and Page 2 is at \$800.
Some amazing effects can be achieved by cycle counting, reading
the floating bus, and racing the beam while toggling graphics