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Newsgroups: comp.sys.atari.8bit
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Message-ID: <8702040003.AA17489@h.cc.purdue.edu>
Date: Tue, 3-Feb-87 19:03:58 EST
Article-I.D.: h.8702040003.AA17489
Posted: Tue Feb  3 19:03:58 1987
Date-Received: Wed, 4-Feb-87 07:27:31 EST
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	I am constructing a set of boards, along with some modifications, to
allow an 800 to emulate a 256K Newell-enhanced 800XL or whatever.  The questions
I have are 1) what locations are switched in/out when RAM is substituted for the
operating system/etc?  I assume that the locations switched are $c000-$cfff and
$d800-$ffff, but I am not certain what is mapped into $c000-$cfff if the OS is
not deselected.  The hardware at $d000-$d7ff is never switched out, correct?
	Secondly, the not-halt signal is not "easily" available to the slots in
the 800.  Would it make much difference if I simply set it up that one of the
bits in $d301 switched an alternate bank of RAM in at $4000-$7fff (the one that
means 'put processor on alternate bank') and let Antic fend for itself?  This
shouldn't be a problem for most programs, because Antic is usually somewhere
up above $8000 anyhow.  This would mean that Antic is on the alternate bank
whenever the processor is.  That might create some problems, so I may try to
route the not-halt signal from the CPU board.

	Alos, does anyone out there have much experience etching circuit boards?
Or know where I can have some etched?  I bought a starter kit from DATAK, but I
don't know if I have the skill to draw this thing up as a photographic image.  I
think I could lay it out, as a general guideline, but the boards are going to
have to be double sided, so I am wondering if there is somewhere I can send the
plans and have the boards made for me.  Along those lines, since I am planning
on (sooner or later) making this into a set of boards (3, with an expansion port
on one of them- I've already got some things to add there) is there any
interest in the world of 800 owners for something like this?  I may write up
a paper, describing the necessary mods, etc.

					Scott Mark



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