Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!snorkelwacker!apple!oliveb!pyramid!athertn!alex
From: alex@athertn.Atherton.COM (Alex Leavens)
Newsgroups: comp.sys.atari.st
Subject: Re: Help Needed with Atari H/W interfacing.
Message-ID: <16686@laurel.athertn.Atherton.COM>
Date: 16 Jan 90 16:26:50 GMT
References: <2706@gos.ukc.ac.uk> <3427@falcon.ukc.ac.uk>
Reply-To: alex@Atherton.COM (Alex Leavens)
Organization: Atherton Technology, Sunnyvale, CA
Lines: 31


There was an article in START (like the first or
second issue), which discussed a novel way of writing
to the cartridge port;  basically, it involved having
some decode logic in the cartridge which took an
address read by the user program, and turn it into
an outgoing data byte.  Thus, if the user program needed
to _write_ a 0x5F to the cartridge, it would _read_ from
address 0xXXXX05F, where 0xXXXX was in the cartridge's
address space.  The act of reading this address would
cause an output of that value to the device on the other
side of the cartridge.

One problem was that there was no addressing involved;
the device on the other side had to know where to stuff
that byte.  I don't think it would be too hard to extend
the logic of the article to provide a limited addressing
capability as well (if I remember, there were 7 bits unused
by this scheme, so you theoretically could get 128 addresses
using an extension.)


|-------------------------------------------------------------------------|
|--alex | alex@Atherton.COM |  Caution!  Falling Opinions, next 6 miles   |
|        Now who are you gonna believe--me, or your own lyin' eyes?       |
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-- 
|-------------------------------------------------------------------------|
|--alex | alex@atherton.com |  Caution!  Falling Opinions, next 6 miles   |
|        Now who are you gonna believe--me, or your own lyin' eyes?       |
|-------------------------------------------------------------------------|