No sumcheck code in a '95 MEMCAL

[Roger Heflin]

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/
> 
>