I would change the emphasis, Ed. Don't you think it's better to say, "The '816, once it has been switched into Native Mode
and one has begun altering the two mode selection bits, is a very different machine"?
What I'd hope to make clear is that the '816 in Native Mode is really
not a very different machine unless one deliberately and actively chooses to go that route. This is important from the POV of 6502 folk, some of whom feel intimidated by the '816, and needlessly shy away from it.
Wisely, the '816 designers arranged that, when the user moves from Emulation Mode to Native Mode, what greets him/her
is a rather 6502-like machine. By default,
m and
x select the familiar 8-bit modes for A and for X and Y
unless the user actively chooses otherwise. Likewise, S defaults to its familiar location in page 1. As Garth says in his
65816 myths article, "It's not a package deal. Instead, there's a lot of freedom to order "à la carte" or treat it like a buffet table. Choose what you do want, and leave the rest alone."
It's true that certain Native Mode changes are not optional, but a great deal of ordinary 6502 code will run just fine in Native Mode. Even...
Code:
TSX
LDA $0101,X
... will be alright unless the user has failed to initialize the Stack Pointer to $FF. In the lead post Andre mentioned remapping S so it no longer points within page 1... and
that constitutes a step into new territory. But it would be an active choice, not something forced upon the user.
-- Jeff
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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
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