Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.os.msdos.programmer
Subject: Re: Programming the keyboard port
Message-ID: <26da66fa@ralf>
Date: 28 Aug 90 12:45:00 GMT
Sender: ralf@b.gp.cs.cmu.edu
Organization: Carnegie Mellon University School of Computer Science
Lines: 15
In-Reply-To: <328@saxony.pa.reuter.COM>

In article <328@saxony.pa.reuter.COM>, dgil@pa.reuter.COM (Dave Gillett) wrote:
}Basically the right answer, except that the 8086 architecture allows for 16-bit
}port addresses, so that's 64K in and 64K out.  IBM only ran ten bits of the
}port address out to the expansion bus, but that's still 1K of each and not 256.
}(I think I've seen MCA port addresses higher than 1K, but I'm not 100% sure.)

Er....	All 16 I/O address bits are available on the bus, but only the low
10 bits are decoded for motherboard devices on pre-PS2 systems (thus the clock
chip appears not only at 0040h-0043h, but also at 0440h-0443h, 0840h-0843h,
etc).
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