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From: foss@iris.ucdavis.edu (Jim Alves-Foss)
Newsgroups: comp.os.msdos.programmer,comp.sys.zenith,comp.sys.ibm.pc.misc
Subject: Re: Programming the keyboard port
Message-ID: <7576@ucdavis.ucdavis.edu>
Date: 15 Aug 90 20:25:50 GMT
References: <90226.104110TOMIII@MTUS5.BITNET>
Sender: usenet@ucdavis.ucdavis.edu
Reply-To: foss@iris.ucdavis.edu (Jim Alves-Foss)
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Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
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In article <90226.104110TOMIII@MTUS5.BITNET> TOMIII@MTUS5.BITNET (Thomas Dwyer III) writes:
>...
>Ok people, how can the same port be both read-only and write-only?  Am
>I missing something? 
>...
>Thanks,
>Thomas Dwyer III                            TOMIII   @ MTUS5.BITNET
>Network Programmer                          DWYERIII @ MTUS5.BITNET
>Computing Technology Services
>Michigan Technological University

Well, In the PC architecture we have 512 (not 256) ports. 256 are Input ports
and 256 are Output ports. Often a card will have a R/W register with a
single address. In your case you have TWO DISTINCT registers, one input
and one output but with the same address (064H(In) and 064H(Out)).

Hope this helps.

-Jim Alves-Foss (foss@iris.ucdavis.edu)  /* Of course these are MY opinions */
                (foss@[127.120.57.20])   /* and may change without warning. */