Re: 747 checksum

[rr <RRauscher@nni.com>]

Yes, you are correct. The '747 eprom checksum starts at byte #4, counting
the first byte in the eprom as byte #0. All '747s are the same.

First two bytes are cksum, next two are prom id. Then they start
adding up the checksum.

BobR.

Niinikoski, Juha wrote:

> > -----Original Message-----
> > From: Programmer [SMTP:nwester@eidnet.org]
> > Sent: 27. heinäkuuta 2000 6:46
> > To:   gmecm@diy-efi.org
> > Subject:      Re:  747 Rom Emulator / status
> >
> > Cool---looking forward to it. Some GM c'sums are added right after the ID
> > byte--other older ones are
> > calc'd right after the checksum bytes...Programming 101 is correct for
> > that
> > type of PROM--and I do believe
> > that's what is stated in the text.
> > Lyndon.
> >
> >
>         What I managed to find out 747 rom (fixed part of code) start
> calibration rom checksum calculation from fourth byte, not immediately after
> checksum. If your claim is true there are different kind of 747 boxes
> around. Is this true ?
>
>         Juha