EST Systems

[dn]

To revive an old thread, I think I may have stumbled onto the  key  to
the GM 7 pin ignition module.  After seeing on some thread a reference
to  the Motorola MC3333 ignition control chip, I started browsing some
of my data books for ignition controllers and remembered that  Allegro
Microsystems makes  a  lot of specialty automotive chips.  I looked in
their automotives section, and sure enough, they make a  chip  called,
appropriately  enough,  an  Electronic  Spark Timing Controller, their
part number ULQ2460A.  After reading through the data sheet, it struck
me that the device they were describing matches the info that  I  have
on the GM 7 pin module EXACTLY!  

The    chip   is   "intended   to   interface   between   conventional
electromagnetic pickups, a computer controlled electronic spark timing
(EST) computer, and a high efficiency ignition coil" (quoted from  the
databook).  They  even  call it an EST!  After looking more closely at
the data sheet, they describe an application schematic where there are
3 connection points to the computer:

1. Reference	-	signal conditioned output from the pickup

2. EST  (Electronic  Spark  Timing)	- control input from the EST
computer, allows the CPU complete control over ignition functions

3. Bypass	-	causes  the  device to internally process the Reference
signal to control dwell, spark timing, and spark advance  without  the
aid of the computer

Coincidence? I think not! Of course, the applications schematic  shows
a  few  external  components,  including some RC time constants, a PNP
darlington coil driver, etc., but the description is almost  word  for
word the same as GM's own description of the module.  The good part of
all  this  is  that  the  data  sheet lists all the thresholds for the
inputs  and outputs, and gives an internal schematic of the chip which
shows the innermost secrets of the device.

For anyone who is interested, the address for these guys is:

Allegro Microsystems Inc.
115 Northeast Cutoff
Box 15036
Worcester MA 01615
Voice (508) 853-5000
Fax   (508) 853-5049

You should be able to  call  their  Customer  Service  department  and
request a  free  copy  of the databook.  Also, if you lie through your
teeth  and tell them that you're going to buy 10,000 or so units, they
can probably be convinced to send you some free engineering samples.


| Specific to jwharris:

| I recall in an earlier message in this thread you said that you  had
| access  to  schematics  of  the  modules,  I wonder if it would be a
| breach of confidentiality to confirm whether or not this is the main
| component of the Delco module?  If not, it will save me and probably 
| others a lot of time dinking around  with a scope  under the hood of 
| the ol' Chebby.  If so, I  think  that I have sufficiently convinced
| myself that this is, indeed the heart of the EST "7 pin" module  and
| I will proceed merrily on from here.

regards
dn





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