[Gmecm] Re: Piggyback ignition modules

[davesnothereman at netscape.net]

Reply to Andrew Gibson:  Multiple responses included.

You said:
"They list the max as a 8 bit value of 00. With the value they claim is 
right (all the 7748 bins have it at 00 there)"
Your information might not be completely correct.  There are different 
"masks."  A "mask" is a way to describe where in the calibration the 
tables are.  There are at least two different locations for the maximum 
timing limit based on the masks in the .bin library.  See below:

ACMC mask 48
ref angle @ 0xC08C  = $AB
maximum limit @ 0xC08D  =$0000
minimum limit @ 0xC091  =$FF8E
fixed timing value @ 0xC094 = $FF6C
fixed timing value @ 0xC091 = $FF8E

ASAX mask 8C
ref angle @ 0xC0E9  =$AB
maximum limit @ 0xC0EA  =$0000
minimum limit @ 0xC0E9  =$FF83
fixed timing value @ 0xC0EE = $FF8E
fixed timing value @ 0xC0F1 = $FF83

In both masks, if the fixed timing value is used, code will compare 
minimum limit to fixed
value and use the larger of the two.  The fixed value should be 
adjusted if the reference angle changes.

You wrote:
" I have found 3 places that are FF83, FF8E, and FF6C that are more 
likely right. "

Sounds like you may have the $48 mask.  But these are not maximum 
values.  They're minimums. Hex values can be signed or unsigned.  An 
unsigned value is assumed to be positive.  A signed value is negative 
when the first bit is one.  For 16 bit signed values, use this number 
line:

-3      -2      -1      0       1       2       3
$FFFD       $FFFE       $FFFF   $0000       $0001       $0002       $0003

Sorry if the spacing is off.   Signed values range from -256 to +255 
decimal or $FF00 to $00FF.

You said:
  "the math that Shannen gave us earlier doesn't work. Nor can it work 
with any of the other timing tables in the bin."
It certainly should.  Pick a value, say 30 degrees.  30 - 60 is -30, 
which is $FFAB.  Check the limits:
Max =    $0000
desired =$FFAB
Min =    $FF8E
 $FF8E is more negative than $FFAB, which is more negative than $0000.

You said:
"The table locations are in different places and different sizes. "
That's what the "mask id" describes.

You said:
" would also like to see if I can make the 7748 switch from a 4 cyl id 
to a 6cyl so I can get a full rpm range and not have to add 50% to 
everything that is related to rpm. "
Not gonna happen without modifying the code.  Both the $48 and $8C mask 
as well as the distributor based '165 4 cyl s10 calibrations are 
dedicated to 4 cylinder engines.  They do not have the code to 
compensate for different numbers of cylinders.  You would have to 
change what the code does, not just the values it works with, to 
accomplish this.  Could you switch to a 7730 or 7749?

You also said:
"I zeroed all the timing tables and base timing in the prom. Saying the 
truck runs like crap is the understatement of the year."
By base timing you mean the reference angle?  There are several other 
timing values and possibly other tables which you may not have access 
to.  There are various spark bias values which are added to or 
subtracted from the main timing tables for different reasons and at 
different times.  These could have altered the delivered timing to make 
it lkess than zero degrees.  You're better off leaving the timing 
tables intact, as maximum timing would be locked at zero anyway.  Also, 
have you tried leaving EST and BYPASS disconnected?  If the engine runs 
poorly in this configuration you can check the problems you mentioned.  
If it runs better, then your basic configuration is good.  You probably 
already know that, HEI modules and pickup coils are specific to 
distributor rotation direction.

About scopes:
"Oh yeah. Please don't take any offense Zaphoid, since I don't mean 
any. I do have a really nice dual trace handheld digital lab scope. "
No offense taken.  Your automotive scope is similar to one I have at 
home.  It's a good tool, but I'm sure you know that it's not really a 
true lab scope.  Automotive scopes need to be user friendly (read: 
simple to use) and very rugged.  My experience is that most auto techs 
couldn't figure out how to correctly use a "true" lab scope.  There's 
just too many features.  I suggested Ebay because you can buy some very 
nice, older lab scopes for an eighth of what you paid for yours.  
They're not automotive grade instruments, but they'll certainly help in 
checking timing signals.  Obviously, you've already got one.

And you said:
"(Hey look guys I have a 8 channel scope that I can't figure out how to 
work the windows based software. Isn't it cool! (Heavy sarcasm))"
I wouldn't replace the Modis at the shop.  I have no trouble using the 
scope functions.  But I can see where some might.

Good luck.

Zaphod
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