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Re: 6502 illegal opcodes questions

Am 19.05.2006, 16:37 Uhr, schrieb <heuser.marcus@freenet.de>:


I guess, all of us have some wishes for design changes and I agree with
your propositions (though I would've called it TYX - sounds better).


You could need both, TXY and TYX. Also PHX/PLX/PHY/PLY would have been
nice and propably would have been possible with only few extra transistors.


For a long time I wished for a block move instruction but I've already
seen too many cases of non-contiguous blocks. A block fill on the other
hand...


And then we would have ended up like the Z80: That a copy loop is faster
than the actual block copy instruction :D

Anyway, you don't need block fill since you can use block copy for filling
too, just write the fill-byte to the start address and then start copying
to bufferstart+1, it will do the same.

Anyway, things could have been better but at the same time they could have
been way worse. We're actually pretty lucky with the existing implementations 
of the 6502 and also VIC + SID.