Re: 6502 illegal opcodes questions

["Michael J. Mahon" <mjmahon@aol.com>]

Cameron Kaiser wrote:
> "Michael J. Mahon" <mjmahon@aol.com> writes:
>
>
> > > The C64 mainly needed it for its text mode. Unlike the Apple, the 
> > > character shapes reside within the Video chip's AND the CPUs normal 
> > > memory map, are read over the normal address bus, and can be redefined 
> > > by pointing a register to RAM instead of ROM.
>
>
> [...]
>
> > It was a conscious choice to make the Apple character set fixed.
> > (And it's nice to have a character set fully defined at power-up.)
>
>
> This is a marginal diversion, but I'm not sure what you mean by "fully
> defined" since the C64's is, of course, also fully defined in the sense
> that it's there. :)

I meant that there was no SRAM to initialize to provide a character
set--but perhaps I misunderstood the explanation of character generation
in the C=64.

-michael

Parallel computing for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."