IBM 5271 (PC3270) host interface options
M H Stein
dm561 at torfree.net
Tue Nov 27 17:49:40 CST 2007
Date: Tue, 27 Nov 2007 22:22:09 +0000 (GMT)
From: ard at p850ug1.demon.co.uk (Tony Duell)
Subject: Re: IBM 5271 (PC3270) host interface options
> What was special about slot 8?
In a true-blue IBM PC/XT (5160) or PortablePC (5155), and AFAIK very few, if
any clones, the data bus on slot 8 is wired to the opposite side of a bus
buffer to the data bus to the other 7 sltos. For that reason, the card in
slot 8 has to assert (pull low) one pin on the conenctor on read cycles
to that board (I forget the exact pin, I can look it up if you need it).
The IBM Async card (RS232 card) was one card that could do this (jumper
selected). I have heard that one reason such a card was included with
every PC/XT was that it was bout the only thing that could go in slot 8,
and by putting it there at the factory it avoided too many calls from
customers 'Why doesn't the XYZ card work properly in my new XT?'
Wasn't it used (and intended) for the expansion chassis card?
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