Calculating the Checksum

Bruce Plecan nacelp at bright.net
Fri Sep 11 01:51:12 GMT 1998


-----Original Message-----
From: Roger Heflin <rah at horizon.hit.net>
To: EFI List <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, September 10, 1998 9:38 PM
Subject: Re: Calculating the Checksum


Checksums are usually by prom type (gm)
2732 series stored at 0000+0001, starts at 0004
27128 series stored at 0006+0007, starts at 0008
27256 series stored at 0006+0007, starts at 0008
27512 series stored at 4006+4007, starts at 4008
Cheers
Bruce

>Well, on a 93 Z28 A4 that seems to be where the checksum is also.   My
eprom is a 32k eprom.
>It is going to have to be the same address for all chips used in the same
ecm, I think the builting stuff may check the checksum to know if the chip
is good.
> Roger
>On Thu, 10 Sep 1998, Ross Myers wrote:
>> After my recent experience in disabling the VATS check, I am now
wondering how the Checksum is calculated.
>> For the VATS it was kinda easy, as the disable signal ment taking 10h off
$0014, then taking 10h off the checksum bytes $0006 & $0007 (This is the
same address for 88 & 89 Vette isn't it?, anyway it worked, no code 51, and
checksum was still enabled).
>> But lets say I change lots of values, what bytes get left out of the
>> checksum value?. I know you don't add all of them up, so where?
>> Is it the same address' for all chips used in the same ECM?.
>> Thanks
>> Ross Myers





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