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From: edp367s@monu6.cc.monash.edu.au (Rik Harris)
Newsgroups: comp.sys.amiga.tech
Subject: Re: cia-b
Message-ID: <1990Aug31.000652.27385@monu6.cc.monash.edu.au>
Date: 31 Aug 90 00:06:52 GMT
References: <5172@uafhp.uark.edu>
Organization: Chisholm Institute of Technology, Melb., Australia
Lines: 30

bbs00049@uafcseg.uucp (Red Roger) writes:


>Hi i've seen some code that uses the ciab serial port set register. 
>what is the real address of this register ??
>bfd000 or bfd0fe - the reason i ask is that in the RKM h/w manual it says 
>bfd000 yet this code works with it at bfd0fe 

From the hardware point of view, it's quite possible that it works with
any even address from $bfd000 to $bfd0fe (including $bfd002, $bfd004, etc).
This could also be true for the other hardware registers in the $bf[de]xxx
range.

Some computer designers just decode the top address lines, and ignore the 
lower lines that specify an individual address.

Since the 68000 has a 16-bit address bus, it may be only mapped to even
addresses.  (the 68000 has no A1 pin, but instead has UDS and LDS or 
upper and lower data strobe, for odd and even chipbanks).

Anyone else have some firm evidence?

rik.
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Rik Harris - Faculty of Computing and Information Technology,
             Monash University, Caulfield Campus (was Chisholm Institute)
edp367s@monu6.cc.monash.edu.au     <-- what the computer says it is
edp367s@monu6.cc.monash.oz[.au]    <-- SEEMS to work more reliably
Build a system that even a fool can use, and only a fool will want to use it.
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