No sumcheck code in a '95 MEMCAL

[David A. Cooley]

According to some documentation I found, the 94/95 Lesabre has a byte
($8006) that if set to $00 it does not use a checksum...
It's set to 00 in all 3 mem-cals I have found for this PCM, and there is no
code in the PROM that references back to $8006.
-----Original Message-----
From: Roger Heflin <rah at horizon.hit.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, November 05, 1998 10:44 AM
Subject: Re: No sumcheck code in a '95 MEMCAL


>
>
>Question:
>
>Do we know if the actual checksum program is on the prom (the one
>that sets the code) is actually in the prom?  I would think the that
>code that actually verifies the prom is good would need to be
>elsewhere.  I was also under the impressions that the checksum code
>was really just a do nothing loop of sorts, maybe they decided to do
>something else there.   The code to to the checksum could actually be
>someplace else in memory (maybe built into the cpu rom?) and
>calculating the prom and deciding if the prom is good or not.
>
>I will have to look at my 93 Z and see if it actually has checksum
>code in it.  If anyone else wants to look it it, it is at:
>
> http://www.hit.net/~rah
>
>I am still working on its disassembly.
>
> Roger
>
>On Wed, 4 Nov 1998, Ludis Langens wrote:
>
>> I've been disassembling a MEMCAL from 1995.  It's BCC BKLL1692, used in
>> the 16196401 ECM.  It's for a W-body with the VIN X 3.4 SFI DOHC
>> engine.  The 32K byte EPROM (27C256) has the standard 9 byte P4 header,
>> but the sumcheck field doesn't match the computed sumcheck.  Further,
>> the program code does not contain a sumchecking subroutine!
>>
>> Has anyone else found a MEMCAL like this?  Could this be in preperation
>> for OBD II?  (This MEMCAL&ECM are just OBD I.)
>>
>> --
>> Ludis Langens                               ludis (at) cruzers (dot) com
>> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
>>
>>
>
>