Daydreaming at Cone Shaped Hat Headquarters

[Ludis Langens]

"Hey You!" <nacelp at bright.net> wrote:
>   To me, the perfect plan is this take a 1227747, and a minimum
> chip for it.  Why a 747, here's why.  It has a pair of P+H outputs
> it's MAP, can be used with 6s or 8s, has a Knock sensor.  With
> a little work I think we could interface a ford MAF for those that
> have to have that.  It would be a P+P for alot of applications.
> It has room for TTC (and some oem appl didn't use that), so it
> would work fine with a manual trans.  It's cheap, and easy to find.
> It's been well hacked.  There are other advantages to this one,
> but for BW I'll refrain.  IF this goes well then we can try the larger
> prom'd ones, or do a turbo ecm, and I got a bunch of ideas for
> further projects this being the leap off one!.

It's not clear if you want to use the existing GM code in the '747, or
to "roll your own."  If the former, you're pretty much limited to
applications similar to the OEM usage.  It becomes just a table hacking
project.  You haven't moved away from the status quo where everyone
picks the OEM ECM best matched for their project.

If you want to "roll your own", there's 8K bytes of soldered in ROM in
the '747 that wants to do things it's way.  [Stare at disassembly]  You
_could_ make an EPROM that intercepts the ROM and never returns.  After
key-on, before interception, the ROM will have run it's init code and
one pass of the spark function.  Your EPROM would have to dedicate a few
locations to keep the ROM happy until you gain control.  All of your
code and data would have to fit in the less than 4K bytes of remaining
EPROM, though you can use a few subroutines in the '747's ROM.  You also
won't be able to use the (one) hardware interrupt, though the GM
hardware will let you poll for it.

If you want to "roll your own" and not be bothered with any of the ROM,
there's a way.  The 1226869/1226870/1227170/1227302 qaudruplets have the
EPROM (aka MEMPAK), CALPAK, and CPU on a little daughterboard.  There is
also a way of electrically disabling the ROM.  I've thought of making a
replacement daughterboard that turns off the ROM and provides a socket
for a 27256 (32K*8) EPROM.  Then the ECM would be fully at my command. 
I suspect the same thing is possible to do with the '747.

But, I've decided that the daughterboard project is a stupid idea.  For
the expense and time to make a daughterboard, I could obtain several
1227730 ECM's.  They already have the ability to use a large EPROM to
hold all the program code.  Plus, the CPU is faster, there is more RAM,
more and better I/O, and a much faster ALDL interface.

If you still want to write custom code for the '747, I've got the
registers of the C3 chipset mostly figured out.  I'm willing to share
this data after verifying it some more.

As to the MAF, why use a Ford?  The C3 chipset in the '747 already has
the ability to handle a GM MAF.  Worst case, you'd have to connect a
CMOS buffer/interface between the harness connector and one of the 40
pin DIPs.

Could someone with a '747 trace out the following parts of the circuit
board?  Find the 40 pin dip marked 16023263 (aka 23263.)  Trace out
where pin 30 is connected.  (That's the MAF input.)  It may go to pin 14
of a chip marked 16043538 (aka 43538.)  If so, trace out where 43538 pin
15 comes from.  It should go through a resistor network and then to the
harness connector.  If 23263 pin 30 instead connects to a chip marked
16004773 (aka 4773), that is the output of a 4049 CMOS buffer.  Find the
corresponding input and continue tracing it back.  There is also a
chance that 23263 pin 30 is simply grounded.

               unsigned long BinToBCD(unsigned long i) {unsigned long t;
Ludis Langens     return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) + 
ludis at cruzers.com            (t + 858993459 >> 2 & 572662306) * 3) : 0;}