Point in the right direction

[Shannen Durphey]

Kevin Grover wrote:
> 
>  Once I have the code I'm guessing things arn't going to be very clear what is what, is there some sort of guide that others have put together?  Or is there some way to decipher the code?  Thanks.

Once you get the code disassembled, and this will not be done by the same
program that assembles, you'll have uncommented assembly to look at.  It's in
text format, of sorts.  There's a random sample below.  You'll want to click
over to Motorola's site and find the pink book for the processor in the ecm
you're working on.  Then you'll want to dedicate lotsa free time to working out
various aspects of what the code does.

Think of it like getting directions from somewhere, to somewhere, in 10 foot
increments.  If the trip's any length, you'll be looking at thousands of
instructions that don't mean a dang thing.  

So it also helps to have a spare ecm set up on a test bench to work with, or a
spare car with an expendable engine.  This way you'll be able to test various
ideas about what code sections do.  I've found it helpful to locate a simulator
for understanding what the actual instructions mean, and how they work.  This is
software and is downloadable.  I think the one that was the easiest to use is
called sim68.  It's an MS-DOS app.  Also, keep good notes.  It's amazing what
you think you'll remember until you actually need it.  It really sucks to spend
a night or two pouring over code only to have to repeat it because your notes
are bad.  Also helps to print everything out.  The pink book, the disassembly,
everything.  Buy a ream of paper and a print cartridge and just do it.  It
wouldn't hurt to try to find a schematic of the ecm.  I'll tell you from
experience that without knowing at least a little bit about what the hardware
does, and how it works, you can get really confused just looking at the code. 
Be ambitious, be persistent, be willing to climb a steep learning curve.  You
can grasp it with time.
Shannen

C98C	LC98C:	ldaa	#0x80
C98E		jsr	LC5AF
C991	LC991:	staa	*L0077
C993		ldx	*L000E
C995		cpx	L88F7
C998		bls	LC9E5
C99A		ldab	L88D9
C99D		bitb	#0x02
C99F		beq	LC9B9
C9A1		cmpa	L88F9
C9A4		bls	LC9B6
C9A6		brset	*L0059,#0x10,LC9DF
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