🚀 go-pugleaf

Re: where to put the memory...
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The 65816 sounds like a very nifty idea to me, but certainly no substitute for
buying an ST if you desire one.  As an upgrade for the 800XL, it would be
desirable to keep everything as compatible as possible.  Since Atari has
already devised a scheme for banked memory in the 130XE, and CDY and others(?)
have successfully and compatibly extended that scheme to at least 262K, it
would make sense to keep the current banking scheme.  See Mapping The Atari,
1985 edition, Appendix 16, page 238, for a full description of the 130XE
memory management scheme.  Basically, they put the extra memory into the 65K
memory map by replacing the original 16K segment between $4000 and $7FFF
(decimal 16384 to 32767).  Location $D301 (decimal 54017) controls the bank
switching.  Two bits there are used to control which of four possibilities
occur with regard to whether the CPU or the ANTIC chips stay with standard
memory or use the selected 16-K bank of extended memory.  If you add more than
131 K but stay with their conventions you can always switch to XL/XE
compatibility mode to run "old" software.  Note that with this arrangement,
both the low memory area and the high ROM area are unaffected.  This is why
everything still works (can be made to work easily).

Re: why to do the conversion
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I concur that the reason for the conversion is to get more addressing
flexibility within the 65K memory space.  A whole lot of assembly language
programs will be easier to write and more compact with the extended
instruction set.  If the 65816 in fact is truly object-code upward compatible
with the 6502, I for one am CERTAINLY going to want to drop one into my 800XL
even though I bought it basically as a toy computer and for use in ham radio
applications and general electronic fooling around.  This will in no way
affect my interest in adding an ST to the collection for more serious work.
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By the way, does anybody know when this chip will really be available; where;
and how much?  I would appreciate solid info.

						John Sangster
						jhs at mitre-bedford.arpa