Promgramming 101

[Bruce]

Just in quick review.
An ecm is a small computer.  It needs instructions on what to do.  For the
purpose of this project I'm going to be talking about the early GM ecms.
In some cases the entire programming is removeable with what is called a
memcal, and in some other cases there is a removable Eprom, with Read Only
Memory that is soldered to the Printed Circuit Board.  With a memcal type
ecm you have full access to the programming (these being a P4 series), and
with the eprom type (C3) you can only work with part of the programming that
is removable.   There is info., at Incoming about how to modify a 747 (C3)
series, so that all the programming can be put on a removable eprom, and
then you can treat it as a P4 in requard to programming.  I will be talking
about what I'm working on which is a 148 (C3) that has been modified to use
a removable eprom.

The GM ecm has under gone a huge change since it's early days.   While the
new ones are written in C, and rather slick, the early ones, can suffer from
odd appearances.  While all the code was written in offices, there is a
difference from that to actually running the car.  So as the *calibration*
guys ran into problems in th real world, they would phone in with the
problems, and the software guys would come up with a patch and transmit the
new code to the guys in the field to continue testing.  So at times the code
looks patched together, because it actually was.   You'll also come to find,
references to the HUD, heads up display.  Well, it's not what you think.
It's just a display that sits on top of the dash with readouts.  Not at all
like seeing the images reflected back off of the windshield.

Needless to say ecms, can't read english.  They read machine code.  There
are numerous machine code languages.  In the C3 series, they used Modula,
and in the later ones "C".

To go from what us humans want to a given language to machine language
requires that it be assembled, so that the ecm can read it,  this is done
with an assemblier.  All it does is take a written english composition, and
translates it to a .bin file so the ecm can follow those instructions.  Now
if you have a .bin file, that you want to read you have to disassemble it,
and that takes a dissasemblier.

Now, we have the various bin codes, and disassembliers, so the next trick is
understanding what the disassemblier means.   This meand getting the Pink
Book out and reading up on the nmuemonics.  Once we understand them, then we
can comment the code, and see exactly what is going on.

Now, as like in the past this is mean to be general in nature.  So if your
ecm varies a little, well GM does have the option to make life hard for us.
If I've made an error please write me off list rather then fill up the
archives with a million references to Promgramming 101A.
If you have a particulat assemblier, or disassemblier you like please
mention what it is.  If it's freeware/shareware so much the better.
If you want to follow along, go to the Motorola site and ask for a Pink
Book.  The exact address is in the archives.
I'm addressing this as I understand things, and trying writting about it as
to cover the none software edumacated folks, ie those like myself.
If you have something to add, but don't want to get too involved, just mail
me, and I'll use the info and keep you out of it.
Cheers
Bruce



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