Re: Apple II Emulation in HyperCard

["Jonathyn Bet'nct" <jonrelay@napanet.net>]

"Mark Cummings" <figjams@primus.com.au> wrote in message
3b9f50c3@news.iprimus.com.au">news:3b9f50c3@news.iprimus.com.au...
> >I'm writing my own Apple II emulator in HyperCard. I have most everything
> >working except peripheral cards, vertical blanking, analog game input,
and
> >hi-res graphics. When I start it up, the emulated processor enters an
> >infinite loop:
> >
> >$D4F0- D0 F8      BNE -8
> >$D4EA- B9 FB 01   LDA $01FB,Y
> >$D4ED- 88         DEY
> >$D4EE- 91 9B      STA ($9B),Y
> >$D4F0- D0 F8      BNE -8
> >
> >I jumped to this address in ApplePC and it is a real infinite loop. I
think
> >there's something wrong with how I initialize something or with the
> >processor emulation.
>
> No idea what you are trying to do here. Is this your code or something
else.

Apparently, it's some code in the Apple IIc ROM.

> >What generates the other 7 bits when you access an I/O memory location
> where
> >only the most significant bit is used?
>
> I think I can help here. The other bits are just random because they could
> be floating inputs, so they could be hi or lo. Whether this is the same in
> an emulator is irrelevant, treat it as if it was.

So I just do this:

if addr=49249 then
  -- hollow apple key
  put 0 into res
  if the commandkey is down then add 128 to res
  add random(127) to res
  return res
end if

Right?

(By the way, the above code is 100% valid in the programming language I'm
using!)




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