Re: Looking for 6502 simulator

[dempson@actrix.gen.nz (David Empson)]

Pim Blokland <pDOTblokland@spcgroup.nl> wrote:

> Mark Percival wrote:
> >
> >>>Long long ago I saw a very nice simulator for the 6502 processor
> >>>on an Apple II. I neither know the name nor where to find it.
> >>It was not a 6502 simulator, but a 68000 simulator.
> >
> > There *is* a 6502 simulator program.  You can find it at;
> > ftp://ground.isca.uiowa.edu/apple2/apple8/Utils/sim6502
> 
> A 6502 simulator on a II? Hm, I don't see what's the use in that.

It is an educational product.  It graphically represents the inner
workings of the processor, so you can see how it executes machine code
instructions.  I saw it several years ago.

It cannot be used to run real programs (there wouldn't be much point).

> There were 6502 *DEBUGGERS*, which could do things like single-step
> through code and the like, and which basically were, on a low level,
> simulating a 6502, of course, but they were not meant to be intended as
> emulators.

I don't think any of these simulated the processor, except for a subset
of the instructions.  Most debuggers work by copying the instruction
into a temporary buffer and executing it directly.  The only
instructions that must be emulated are branches, jumps, calls, returns,
etc.

> One of those was called BugByter, I believe, and was part of the EdAsm
> package.

Yep.  Bugbyter is the prececessor of GSBug (they have similar user
interfaces).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand