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From: ekalenda@cup.portal.com (Edward John Kalenda)
Newsgroups: comp.misc
Subject: Re: Help Hapless Hardware Hacker
Message-ID: <32697@cup.portal.com>
Date: 11 Aug 90 19:57:35 GMT
References: <2930@sodium.ATT.COM> <62399@bu.edu.bu.edu>
Organization: The Portal System (TM)
Lines: 17

> -The board decodes 12 bits of I/O address.  The I/O port address used
> -was 0x250, but I also tried changing it to a few other values to no
> -avail.
> 
> All 12 bits???  There are only 10 bits used for I/O addressing.
> 
> \|/ Michael L. Ardai     ardai@bu-pub.bu.edu   
> --- ---------------------------------------------------------------
> /|\ ...!sun!teda!maven.dnet!ardai (preferred)

Beg to differ, but my IBM XT Tech Ref indicates I/O port addresses as high
as 0x2393 (Cluster Adapter 4) as reserved by IBM. This needs at least 12 bits
of address decode. The 80x86 family can address the full 16-bit address space
for I/O ports so you should decode them all. If fact the schematics show
all 16 bits being fed into the decode logic for the 8253-5 PIA chip.

Ed