OEM EFI computers

FIScot at aol.com FIScot at aol.com
Wed May 31 23:43:34 GMT 1995

I looked at the GM computer system very extensively. (1992 5.7 TBI moel)
That computer uses a 68hc11FN. Nice chip. All of the code resides on the
27256 in the calpack. Thats a 64k byte rom, and the cpu only has a 64k byte
adress space, so I am assuming that ALL of the code is on the calpack. Oh,
yeah, that version of the '11 has programable chip selects too. Anyway,  I
doubt that GM bothered with programing the on chip mask ROM when they had
that big EPROM to use.  I am wondering if the GNX really used the 6801, or if
it was really a 6811. Anyone know this for sure? I would guess that they used
the '11 on the GNX, because its the first production car that GM ever
implimented SEFI on. The coding of a 6801 would be very dificult as compared
with the code required for the '11. The timer section of the '11 almost lends
itself to SEFI.  Oh, yeah, Can I get a copy of the GNX code? Is it
disasembled? Is it comented (yeah, right!) ?


                Using AOL's editor.......  The GM C3's used the masked ROM's,
and the newer (P4?) use the 32Kx8 PROM (27C256) that contains all the code,
at least the 1227730 ECM's that I have been playing with.  I too have been
working the 91 5.7L code, and have just about all the PROM locs defined, and
all the regs.  (I still don't know what the '3FE0' reg is, if anyone knows.)
    The C3 usually had code in the 'E000-FFFF' area of memory, and I've seen
rhe PROM reside in '3000-3FFF' , and 'D000-DFFF', with about half the PROM
dedicated to code, and the other half to the cal tables.     In moving from
the C3 to the 1227730,  it is interesting to note that the 87 Cavalier 4
cylinder that uses the 1227730, uses code that very closely resembles the C3
code in the 1227747 truck TBI ECM.  The 2.8L V-6's from the era also used the
same 1227730 ECM, and the 90-92 5.0 and 5.7L TPI's used the same ECM!  From 4
cylinder to V-8, all with the same ECM.....  I've got just about all the code
to the 4 cyl, V-6 (Both MAF and MAP) and V-8's done.  Interesting stuff,
almost an addiction I'd say!

was speaking of EGR earlier, and I was looking at a file that was labeled
ADSFB350, This chip may be what makes the EPA upset with the aftermarket.  It
completely shut off the EGR function, and then added a bit more timing at WOT
and a little higher number in the slow speed vol eff table at WOT.     Later,
Scot Sealander

I almost forgot!   The C3 seems to have  a hybrid motorola chip.  It has the
instuction set of the 6801 (multiply), but the pinout is nearly the 6802, and
yes the GN computer uses the GM 6801 processor.  GM used that same processor
for over 10 years!

cooldave, if you are reading this, I would like a copy of the binary file for
the GN!  Thanks!

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