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SubjectRe: NES rom FF opcode Reply to this message
Posted byBart T.
Posted on07/06/08 03:37 PM



> > > Hi,
> > > I've built a disassembler for the NES roms to test the 6502 cpu of my nes
> > > emulator. However the disassembler showed many FF opcodes (mostly chained in
> > > long groups of FF op's). I used other NES disassemblers to compare the
> output
> > so
> > > to rule out errors and I also looked at the binary data directly. So I would
> > > like to know why there are so many FF opcodes in Nes roms (e.g. zelda, SMB2,
> > > Ninja Gaiden)?
> > >
> > > Thanks
> > >
> >
> > It's not an opcode -- it's just meaningless data you're looking at. Long runs
> of
> > 0xFF usually mean that part of the ROM has not been programmed with anything.
> >
> >
> > ----
> > Bart
> >
>
> So why do they have these "gaps" in the program? Why isn't the whole program
> (game) burnt on the ROM without them (i.e as one big chunk)?
>

It depends on how they laid it out and how the data and code changed during the development of the game. They may have allocate chunks of ROM space for different sorts of data before they knew exactly how big it would need to be, for example.


----
Bart

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Entire Thread
Subject  Posted byPosted On
*NES rom FF opcode  KMDK07/05/08 08:07 AM
.*Re: NES rom FF opcode  Bart T.07/05/08 02:07 PM
..*Re: NES rom FF opcode  KMDK07/06/08 09:30 AM
....Re: NES rom FF opcode  Bart T.07/06/08 03:37 PM
....*Re: NES rom FF opcode  smf07/31/08 05:54 PM