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From: glen@intelca.UUCP (Glen Shires)
Newsgroups: net.micro.pc
Subject: Re: AT ROM Question
Message-ID: <122@intelca.UUCP>
Date: Fri, 11-Oct-85 19:51:27 EDT
Article-I.D.: intelca.122
Posted: Fri Oct 11 19:51:27 1985
Date-Received: Mon, 14-Oct-85 03:33:58 EDT
References: <581@spar.UUCP>
Distribution: net
Organization: Intel, Santa Clara, Ca.
Lines: 23

> 
> In the IBM AT there are two 23256P ROMS on the motherboard.  I know that
> BIOS sits in one of these at FE000-FFFFF, but what is the other stuff.
> I would like to take a look at what is in these two Roms, and possibly
> change them.  Unfortunately, my prom burner will not read a 23256P.  Can
> someone tell me the adress range that these two chips fall into so that
> I can look at them with debug.
> 
> 	Thanks in Advance
> 	-Chris

The AT has a 16-bit CPU (286) and therefore uses two 8-bit ROMs for the
power-up diagnostics and BIOS.  These ROMs are located at f000:0 - f000:ffff
with the left (U27) ROM having the low (even) address-bytes and the right
(U47) containing the high (odd) bytes.  They are pin-for-pin compatible with
27256 EPROMs but unfortunately not readable by most PROM burners.
The full assembly language code listing with comments is available in the
IBM-AT Technical Reference Manual.
-- 
^ ^    Glen Shires, Intel, Santa Clara, Ca.
O O     Usenet: {ucbvax!amd,pur-ee,hplabs}!intelca!glen
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