Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!unisoft!gethen!farren
From: farren@gethen.UUCP (Michael J. Farren)
Newsgroups: comp.sys.ibm.pc
Subject: Re: PC IO Port bus ?
Message-ID: <831@gethen.UUCP>
Date: 27 Mar 88 15:25:28 GMT
References: <166@ucrmath.UUCP>
Reply-To: farren@gethen.UUCP (Michael J. Farren)
Organization: There's Unix there in Oakland
Lines: 18

In article <166@ucrmath.UUCP> jantypas@hope.UUCP (John Antypas) writes:
>(a) The IBM PC data bus (ie when I do an INP, or OUT port instruction)
>    has address decoding already done?  What about latching?

No.  And, no.

>(b) On the PC, I assume the bus is 16 bits wide (data) with a 16 bit 
>    address bus?  (My AT manual says it is.)

The AT data bus is 16 bits wide, but the original PC data bus is only
8 bits wide.  There is an additional connector on the AT bus, carrying
the extra data bits.  The original PC's address bus is 20 bits wide,
I believe the AT's is 24, but am not sure.

-- 
Michael J. Farren             | "INVESTIGATE your point of view, don't just 
{ucbvax, uunet, hoptoad}!     | dogmatize it!  Reflect on it and re-evaluate
        unisoft!gethen!farren | it.  You may want to change your mind someday."
gethen!farren@lll-winken.llnl.gov ----- Tom Reingold, from alt.flame