Re: Hardware emulation of 6509 using 6502?

From: Mia Magnusson <>
Date: Thu, 19 Jul 2018 22:23:05 +0200
Message-ID: <>
Den Wed, 18 Jul 2018 12:37:25 -0500 skrev Jim Brain <>:
> On 7/18/2018 3:59 AM, Michał Pleban wrote:
> > Jim Brain wrote:
> >
> >> Well, it should not *HAVE* to be rewritten.  It can, though, to
> >> support the '816.
> > If it's not rewritten, how will it access the DRAM when the 816 is
> > used?
> When the unit boots, it boots into 6502 "mode", where $0 and $1
> behave as before.  Maybe I misunderstand the question.

Yeah, and when switching to 65816 mode it can use a disk-loaded kernal
in some other part of memory.

Btw I know I'm feature creeping, but how hard would it be to add a mode
where the video ram from bank 15 is seen at $8000, the rest is ram and
some way of exiting that mode by accessing some address that is an I/O
space of the original PETs? That way it would probably be rather easy
to emulate a PET good enough to run most PET software. 

> >> On a real 6509, if you store $aa at $0 and read it back, do you
> >> get $0a or $aa?
> > It will read $0A.
> OK, thanks.  That makes creating an 8 bit port version of the 6509 a
> bit tougher, but maybe still doable.

Are you thinking about access to 16MB instead of 1MB in 6509 emulation
mode? I think that might need to have an enable/disable function as I'm
sure there are software writing garbage to the upper 4 bits of $0/$1.

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Received on 2018-07-19 23:01:55

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