Re: A few technical q's from an apple newbie

[Mark McDougall <msmcdoug@no.spam.iinet>]

josephoswaldgg@hotmail.com wrote:

> Just to clarify things a bit, it seems that MESS is emulating a IIe or
> later model, or maybe some hybrid II. You might have a hard time
> getting coherent information on the details of the Apple II by studying
> that source.

Yes, that's what I'm finding - it's difficult to know what is and isn't part 
of the ][+, which is why I went to the trouble of implementing the VBLANK 
etc only to find it wasn't required.

> I guess the main advantage is that you get VGA output code, instead of
> the TTL-driven composite video the Apple II hardware produces.

Well, that's neither here nor there for me, as I'm doing a hardware 
emulation and had to 'design' the video logic to suit my own hardware. It's 
interesting b/c you look at the MESS source for the video calcs and they 
have 'nasty' things in there like mutliplication by 5 - all so easy in 
software but horrible if you're trying to do it every dot-clock in hardware! 
Fortunately after working it through I found I could eliminate the 
multiplication altogether - which is not surprising I guess since the 
original circuit design was motivated by cutting corners!

Anyway, I'm sure I'm not too far off being able to play Lode Runner...

I've just got to work out how to load it into memory and execute it from 
there since I haven't emulated *any* storage medium yet... I can only 
pre-initialise RAM contents atm. Thinking about it, it's probably not 
do-able since I recall it read the level data directly off disk... maybe 
Apple Invaders would be a better way to start? Hmm...

Regards,

--
|              Mark McDougall                | "Electrical Engineers do it
|         <http://to be announced>           |   with less resistance!"