PUL/MILE and speed DIVISOR understanding

[Mike Rolica]

Yes you are correct.  Changed  the valve at 0015 to basically 2000, to make
up for optical sensor  (2000ppm )and also changed another bit  .. forget
where it is.... Bruce will know as it is an option flag for either optical
or mag speed sensor  Seems to work as I have tried a few chips with various
values. Tcc locks up sooner and sooner with lower value and higher with
higher value, telling me this is what it does :-) Also have to change input
on ecm for differnet sensor type... bruce knows this as well.

As for 0014 this is for the digital dash option used to calb signal to
speedo  I think.
Mike Rolica
Meridian Magnesium Products
Strathroy, Ont 
Ext. 260


	-----Original Message-----
	From:	Marc Randolph [SMTP:mrand at pobox.com]
	Sent:	Monday, November 29, 1999 12:24 PM
	To:	gmecm at efi332.eng.ohio-state.edu
	Subject:	PUL/MILE and speed DIVISOR understanding

	Here is something for both the beginners that want to learn
	about code and tables, and a question for those that already
	understand most of it:

	In the ANHT 90 L98 ECMGUY .pdf listing, there are two entries that
	I'm very interested in and was wondering if anyone could help me 
	understand them better before I go blindly changing my PROM and 
	getting myself really confused (or worse).  Here's the details of
	what I know:

	Two table entries of interest:

	8014:   FCB $00    ; INSTRUMENT PANEL DIVIDER ARG
	8015:   FCB 230    ; PULSE/MILE ROAD SPEED CONSTANT

	Code of interest:

	At code offset BEF7, the 8014 value is OR'ed with whatever is in

	memory location 0x32 (after 0x32 is masked with 0x0F right below
	BEE9).  0x32 appears to be a word that gets clocked out of
	the ECM serially (on YZ body, 0x32 contains, among other things 

	I'm unsure of, a bit to enable the secondary fuel pump, and a
	bit to control the shift light), I assume to the CCM for display
	on the instrument panel.

	At code offset BF9A, the 8015 value is read into accumulator A and
	then multiplied by accumulator B (which contains a count of some
	kind from the vehicle speed sensor, read from memory location 0x8D).
	This is then divided by whatever is at memory location (0x8B).


	Concepts of interest:

	The ECM converts the vehicle speed sensor signal to 4007 pulses
	per second and feeds that to devices like the CCM, ABS, and ASR.
	The value at 8015, 230dec, is the internal representation of
	the 4007.

	My main question:

	When I go to install taller gears in my car, I'd like to modify
	the ECM to make up for the installation so that my speedometer
	reads the correct speed.  My initial guess is that I should change
	the value at 8015 so that the ECM puts out fewer than 4007 pulses
	per mile.  Since everything else is expecting 4007 pulses per mile,
	if I feed it a few less pulses, they will think the car is traveling
	slightly slower (which is true because of the taller rear end).
	Can anyone think of a reason this wouldn't work (or would do any
	harm)?

	Second question:

	Would the correct pulse / mile value be based upon a percentage
	of the original?  3.45 gears stock, 4.10 gears new, would result
	in an 18.8% difference - is that the right amount to adjust the
	pulses / mile?

	Third question:

	What in the world is the value at 8014 for?  Any ideas how much
	it would divide/multiply the speed by?


	Thank you, and have fun,

	   Marc

	-- 
	  Marc Randolph     -    mrand at pobox.com    -     PGP keyID:
0x4C95994D
	     If you have any info on the mid-60's car called the Bill Thomas
	       Cheetah, or know anyone that might, please contact me.