disassembly of 6803 code

[Arnaud Westenberg]

Ludis Langens wrote:
> 
> Arnaud Westenberg wrote:
> >
> > I downloaded the data sheet for a MC6803E processor. I assume there will
> > be some differences between the processors but also that they use the
> > same instruction set?
> 
> 6803E?  My data books don't show such an animal.  There is a 6809E, but
> that is a totally different animal with a mostly different instruction set.

Well, I have the specs of the beast. If you want I can send them to you.
 
> If you can't find data on a 6803, look for 6801 stuff.  The '01 and '03
> are the same, except that the '01 contains a small amount of internal ROM.

So I assume I can reffer to the standard instruction set of the 6801/3.
The 6803E specs say "Enhanced MC6800 instruction set".

> > Where/how do I start to disassemble the code? Would a disassembler be of
> > any good?
> 
> A disassembler would be very useful.  If you find a 68HC11 disassembler,
> you can probably use it.  The 6801/03 are a subset of the 'HC11.  One
> thing to watch out for is that the 'HC11 has more interrupt vectors than
> the older chips.

I have found a disassembler with support for the 6803 (DASMX) and
disassembled it, it didn't complain. Do I have to check wether it has
done its work properly?

> > Here are the specs:
> > CPU, MC6803U4CPR running at 4MHz in mode 2
> 
> Are you sure it is at 4MHz?  That's awful fast for a 6803.  More likely
> you have a 4MHz crystal and the CPU runs at 1 MHz.  The divide by 4 is a
> normal feature of the 6803.

I just copied the specs from the net and personally never had a look at
it so I can't say if it's correct.

> > but
> > how to figure out that the timer is at $2000-$2007, for example?
> 
> What do you mean?  Are you asking how the hardware set those addresses?
> If so, there will be several small logic chips that decode these
> addresses.  Most likely one or more of them will be a 74LS138 or 74LS139.

Sorry that's not what I meant. When looking at the data sheet it just
says 'external memory space'. Suppose I didn't know any addresses of
external connected devices, how would I determine those addresses.

I have some more questions wich I'll ask in the other replies (you guys
are verry responsive, Thanks).

Thanks

Arnaud
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