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From: stevew@wyse.wyse.com (Steve Wilson xttemp dept303)
Newsgroups: comp.arch
Subject: Re: Instruction (dis)continuation (
Message-ID: <2425@wyse.wyse.com>
Date: 15 Sep 89 15:46:22 GMT
References: <2353@oakhill.UUCP> <261500010@S34.Prime.COM> <34701@apple.Apple.COM> <642@unicads.UUCP>
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Reply-To: stevew@wyse.UUCP (Steve Wilson xttemp dept303)
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In article <642@unicads.UUCP> les@unicads.UUCP (Les Milash) writes:
>i'll summarize (and i'm sure y'all will correct me if i'm wrong:-)
>memory mapped i/o has to be "memory-like" since processors will often assume
>that stuff in the "memory space" is memory-like, even to the point of calling
>its "memory space" virtual and translating to physical.
>

The definition I've always heard/used for memory-mapped I/O was one
which implied that all control to the device was done via memory addresses,
i.e. not using any special I/O instructions such as in/out on the 80x6 line. 
Therefore, any I/O device that is hooked up to a micro such as a 68K would
by definition have to be "memory-mapped" since the 68K doesn't have
provisions for in/out instructions.  The device will react to the decode
of some specific address range presented by the processor.  I've never
heard of said device being "memory-like" as being part of the definition
of this term.  

Steve Wilson