Programming 101

[Bruce Plecan]

If you have not read the past 101 installments, please do so
now.  This is for educational purposes.  Changing the calibrations
of your ecm may violate the laws in your area.  If you attempt
recalibrations, serious engine damage may result.  Please 
read past posts about tune up procedures, when attempting
recalibrations.  These matters should be done under adult
supervision.  Again this is in general for gm ecms, and most 
specically the 1227747..

Were going to talk/write/read some today on the matter of 
malfunctions flags.  They are the self diagnostics the ecm
does, and then reports to you when in diagnostic mode.  
When you short the ALDL two diagnostic pins together the
SES light flashes a code at you, 12 plus what ever the 
malfunction is, if any.  If you need to understand the codes,
there are numerous articles, and books covering that issue,
and should be used for understanding say a code 21.  The
purpose of this article is turning on+off these reports of self
diagnostics.  Notice I say reports.  Some of the self diagnostics
will still run, but not be reported as an error, or result in the
ecm going into limp home mode.  That has also been covered
in the archives, about which ones run, or not..

  Now, these malfunction flag addresses use a combination 
of Hex, Dec, and Binary..  In brief these are different ways
of counting, and the following is a conversion for them

Dec     Hex     Bin
0          0          0000
1          1          0001
2          2          0010
3          3          0011
4          4          0100
5          5          0101
6          6          0110
7          7          0111
8          8          1000
9          9          1001
10        A         1010
11        B         1011
12        C         1100
13        D         1101
14        E         1110
15       F          1111

Now again refering to prior post addresses in a hex
editor of a prom look something like
           00   01   02   03   04   05
0000  AA  03   FF   FA  FD  02

This is a very abbreviated corner of on the columns across
the top would read to 0F, and the rows would go from 0000
to 0FFF.  Now we could read those addresses as binary,
the  0002  would look like 1111  1111
       0003  would be           1111  1100
       0004  would be           1111  1101
Now if we wanted to say 1 represented yes, and 0 would be
no, we could tell the computer that..
Now say we had 24 malfunction codes.  We could list them
as   12,13,14,15,16,17,18,19,20,21,22,23,24,25, and so on..

So address  0002   could mean malfunction codes
  12, 13, 14, 15,        16, 17, 18, 19
and then the 1+0's could mean yes and no.  So looking at 
FF meaning 1111    1111
we would have
12   13   14   15       16   17   18   19
yes yes  yes  yes     yes  yes  yes  yes
meaning all the malfuntion flags at 0002 are enabled, and working.
If we go to 0003 we get            1111                      1100
that would correspond to    20 21 22 23          24 25 26 27
and have the meaning of  yes yes yes yes     yes yes no no
So malfunction flags 20,21,22,23,24,25, would be enabled
and 26+27 disabled..
  Now, on some ecms they use different codes, and skip
numbers, so it gets to be challenging to line up which codes
are used, and which ones are enable, or disabled.  But, in the
747 they are at 050D-050F, and 3 words (addresses) long.
On other ecms they may be 3-4-or even 5 words long, and
probably longer than that on some of the newer stuff.  But,
on the 747 all ya haveta do is try turning them on+off, and
all of sudden by using the SES/scanner, and causing a 
known malfunction you can figure out which 0+1 enables,
disables, what malfunction flag...
  Again please don't quote the whole posting in reply, just
what is is doubt or wrong, or you have a difference in a 
opinion with.
  I am not a EE, ME, or anything like that, so the above is
how I understand things, and make no guarantee that
it is absolutely correct it has worked for me, and your
results, may vary.
  If you have any comments please e-mail me, and I'll
review, what ya say, and see if in fact I did error (again)..
Bruce      nacelp at bright.net
This message originated at Cone Shaped Hat World
Headquarters

If you have not downloaded Terry's gmer.zip, and
what Ludis posted yesterday, you need to read yesterday's
postings in the archives, and do that now.  If you have any
information about the 747 tables/switches, I'd really appreciate
hearing about them, or would you post that information.
If ya haveta read the above a couple hundred times to get
it don't feel bad, I did it more than that to get it......