Re: Difference between R65C02 and original 6502 (wrt 6509 emulation)

Den Mon, 15 Apr 2019 17:08:43 -0400 (EDT) skrev Jim Brain
<brain_at_jbrain.com>:
> Unfortunately, it does not work that way. I understood that the
> $01/$1 registers are present in every bank, not just bank $0. Perhaps
> that is a wrong assumption. As such, I also decode them to each bank.
> (I think it has to be that way, for how else would you move from
> execution in bank 1 to bank 0 if the registers only appear in bank
> 0.) So, a write to any bank: $0/$1 will save new values in the banks
> (though they will not be used until the developer moves back into
> emulation mode).

I might had been unclear.

What I'm trying to say is that if the registers at 0 and 1 are hidden
from read, but listens to writes, in '816 mode, everything should work
fine as the code that switches back from '816 mode to 6509 emulation
could just write the 0/1 registers at $F0000/$F0001 as there is no risk
of corrupting memory for the 8088 board. With those registers written
it's then safe to switch back from '816 mode to 6509 emulation mode and
the registers will contain the correct values even if previous code had
written to $x0000/$x0001.


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