On Thu, 18 May 2000, Charles P. Hobbs (SoCalTip) wrote:
> Apple II's needed a simple hardware hack (a couple of wires or simple
> components) in order to make one of the hardware memory addresses
> correspond to the state of the vertical blanking interval (it would either
> go high or low when vertical blanking was going on). IIe's and IIc's had a
> memory location (hex C013?) that does that for you, no hardware hack
> required. (Although, $C013 behaved in the opposite manner than Lancaster's
> hack did--perhaps $C013 went high when Lancaster's memory location went
> low and vice versa, so Lancaster's programs had to be modified a slight
> bit in order to work).
Ah. Thanks for clarifying that.
Well then this brings me back to wondering how those programs that allowed
mixed video modes on the Apple ][ worked. They required no hardware mods.
Hmmm.
> In any event, once you had the vertical blanking information, you could
> write machine language programs that would switch between Apple graphic
> modes just about anyplace on the screen (within limits). You were more or
> less limited to static displays because of the timimg requirements, but
> you could still do some interesting stuff. I typed in a few of the
> programs, and still have them sitting around on a disk if anyone is
> curious...
The programs I'm talking about I saw as demos on that Magazine Diskette
(Magazette) subscribtion service called SoftDisk (anyone remember that?
lots o' cool stuff on that). And they had hi-res animation mixed with
lo-res graphics and text-mode text. One day I will have to dig those
disks out and dissect the code to figure out how they did it. I don't
know why I didn't try to figure it out way back when.
There was one hi-res graphics game I was writing where I was going to try
to employ this trick and use a text line at the top of the screen to print
out the score. I knew it would involve having to keep excrutiating track
of each instruction cycle in the code to make the timing work. I never
completed this part.
Sellam International Man of Intrigue and Danger
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Received on Thu May 18 2000 - 19:35:59 BST