Motronic

[Scot Sealander]

Chris Denzler wrote:

> So let me ask....Do the gurus approach the task from a software and      
> hardware perspective simultaneously, disassembling the code as well as   
> using test equipment to figure out what, when, where, and how?

I don't see how you can separate the two.  The GM C3 computers used all 
memory mapped I/O, so it is easy to figure out what the code is doing, once 
you have a schematic.  This makes them much easier to start with (and they 
are cheap at the junkyard...).  The only sticking point is that most of the 
code is in masked ROM, soldered into the board.  Once you have a schematic, 
you can attach an adapter to the edge card connector on the board and use a 
PROM reader to get the data out.  The ROM's are gated by the CPU clock, so 
use a latch to capture the data for the PROM reader.  You will get a lot of 
bad reads if you don't.

  The P4's used more custom parts, and more of the 68HC11's I/O to get data 
in and out.  The tough part is that it is not a standard Motorola part, so 
you have to figure out what the regs are used for.  The TPU is also custom, 
so that requires more work.  But a little creativity with a frequency 
generator and using your custom EPROM code you can figure out what each reg 
is used for.  (But you gotta sit down and draw that schematic....)

There is code dedicated to measuring the sensor inputs, and that is tied to 
the check engine light.   If you search the binary file for say, hex 
131415, you just might find the check engine light table.....  The error 
code and masks have a certain relationship with the table.  ;-)

Scot Sealander   Sealand at clarityconnect.com