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From: myxm@beta.UUCP (Mike Mitchell)
Newsgroups: comp.sys.ibm.pc
Subject: IBM ROM Format???
Message-ID: <4342@beta.UUCP>
Date: Tue, 21-Apr-87 13:25:41 EST
Article-I.D.: beta.4342
Posted: Tue Apr 21 13:25:41 1987
Date-Received: Wed, 22-Apr-87 04:24:28 EST
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 19
Keywords: Help!

Hello,

Can anyone explain the format of a ROM which lives in the address
space C8000 to F4000? I am aware that the first two bytes of one
of any 2K increments would need to be 0x55 and 0xAA. The third byte
is the length of the ROM software / 512 bytes. The fourth byte is
the beginning of the actual code.

What is stumping me is the method in which the PC calculates a
checksum on the ROM. How is this checksum derived and what locations
are totaled to get it? My understanding is that the checksum is
only one byte long and should total zero for the ROM software to
be valid.

Thanx for any help.

Mike Mitchell
myxm@lanl.gov OR
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