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Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!hplabs!hp-pcd!bill
From: bill@hp-pcd.UUCP (bill)
Newsgroups: net.micro.pc
Subject: Re: IBM PC/AT Memory Map
Message-ID: <15200021@hpcvlo.UUCP>
Date: Thu, 8-May-86 13:29:00 EDT
Article-I.D.: hpcvlo.15200021
Posted: Thu May  8 13:29:00 1986
Date-Received: Tue, 13-May-86 00:38:16 EDT
References: <697@wjvax.UUCP>
Organization: Hewlett-Packard - Corvallis, OR
Lines: 19
Nf-ID: #R:wjvax:-69700:hpcvlo:15200021:000:834
Nf-From: hpcvlo!bill    May  8 09:29:00 1986


The 64K at segment E000 is reserved for motherboard BIOS extension ROMs.
Even though the ROM sockets on your board are empty, I'd expect that any
attempt to read from them would still enable the 74ALS245 buffers that
isolate the ROM sockets from the system bus; these buffers will hard drive
the bus to some "unknown" state during a read (because of their floating
inputs).

You might try moving your card to somewhere in the C800-E000 range.
This is the address range reserved for plug-in adapter BIOS extension ROMs.
(Your EGA card lives at the 16K starting at segment C000).
Just make sure the block you pick doesn't conflict with any of your other
plug-in cards.  Also, it may be necessary to add a wait state.

You might also get hold of an AT Technical Reference Manual, if you don't
already have one.

Bill Frolik
hp-pcd!bill