[Gmecm] Re: Gmecm Digest, Vol 19, Issue 3

[William Lucke]

Conceptually, I look at it hierarchically:
Hardware
Code
Data

Hardware is the ECM... 7730, 7749, etc.
Code is the mask... $8D, $8F, etc.
Data is the calibration... ANHT, AUJP, etc.

The code consists of instructions that tell the ECM what to with the 
calibration data. When the ECM executes the same code instructions on 
different data sets, you get different outputs. Thus there can be 
multiple sets of calibration data for each code mask, because, for 
example, the speedometer data would have to be different for each axle 
ratio offered in a RWD car, or the calibration data for a 305 is 
different than that for a 350, even though they are run by the same ECM 
and code mask.

The term "mask" is a little obtuse in that it stems from old school 
computer speak. If you printed out the .bin file you could theoretically 
cut holes in another piece of paper to lay over top of the printout so 
that you only looked at what you were interested in... you could then 
label each hole "0xAAAA - 0xAAAF: data so-and-so" and the piece of paper 
with the holes would become a "mask" for understanding your .bin. This 
is exactly what a definition file does in your PC's memory.

Because each version of Code may put critical tables in different 
locations in the .bin, you need a different mask for each different 
code, and thus the term mask has come to be synonymous with the specific 
program used.


Will


> Date: Sat, 2 Sep 2006 19:28:18 +0100
> From: "Robin Handley" <Robin at FuryWorld.fsnet.co.uk>
> Subject: [Gmecm] What really is a 'mask'?
> 
> I've never really known what a GM software 'mask' is - never having seen a
> clear definition of it. I had been beginning to think, of late, that a
> 'mask' (e.g. $58, $8D) is a particular version of GM code, which is used in
> different applications (and given different 4-latter designations e.g.
> ANHT/AUJP) by changing the calibration data only. But now I'm not so sure.
> Could somebody clarify?
> 
> Robin