Path: utzoo!mnetor!uunet!mcvax!unido!tub!tmpmbx!netmbx!hase
From: hase@netmbx.UUCP (Hartmut Semken)
Newsgroups: comp.sys.atari.st
Subject: Re: Writing to the cartridge port.
Message-ID: <1771@netmbx.UUCP>
Date: 26 Apr 88 23:43:31 GMT
References: <8804132155.AA23202@ucbvax.Berkeley.EDU> <542@csvax.liv.ac.uk>
Reply-To: hase@netmbx.UUCP (Hartmut Semken)
Organization: netmbx Public Access Unix, Berlin
Lines: 23

In article <542@csvax.liv.ac.uk> unpowell@csvax.liv.ac.uk writes:
>>   But according to the infamous Abacus book ST Internals, (p96) writing
>> to this address creates a bus error. They tried putting a ram disk in
>> the port but without sucess.
WRITING to the adresses of the rom port does not generate a DTACK respose
and ends in a bus error. READING is possible, of course.
>> 
>>   How did Alpha get around this so that the Megadisk would work with
>> out creating bus errors?
Simple. READ the port and let a littlie GAL take the lower byte of the
adress bus out to the world (RAM or port or write only memory or the like).
>	Who knows? One Meg seems a little optomistic as the ST only has
>128K of address space available for the cartridge port. Where will this
>extra memory go?

It's a RAMDisk. 
The idea is the same as with the EMS boards for PCs: a little window is
"currently" accessed and this window is sliding over the Meg, or two
or...
hase
-- 
Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP
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