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From: jhs@MITRE-BEDFORD.ARPA
Newsgroups: net.micro.atari8
Subject: Adding new peripheral devices on parallel port of 800XL
Message-ID: <8605262234.AA05521@mitre-bedford.ARPA>
Date: Mon, 26-May-86 18:40:22 EDT
Article-I.D.: mitre-be.8605262234.AA05521
Posted: Mon May 26 18:40:22 1986
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Organization: The MITRE Corp., Bedford, MA
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More info:  Appendix 12 of Mapping The Atari, 1985 revised edition, page 215,
confirms what I said in the previous message:  D100 - D1FF is in fact intended
for use in devices attached via the parallel expansion port.  Apparently,
there are some internal registers in this region, but provision is made for
switching them out to allow the expansion port to use the region also.

No mention is made in Mapping The Atari about devices in D200 - D2FF.
I don't know if this means the region is unused or if you get RAM when you
address up there.  (Easy enough to try, I suppose.)  I also don't know how
the external device switching is done, but Pin 2 of the expansion port is
called "external select"  so this may be involved.  I don't know if it is a
signal from or to the external device however.

Does anybody else have comments?

-John Sangster
jhs@mitre-bedford.arpa