Re: Hardware emulation of 6509 using 6502?

Den Thu, 9 Nov 2017 19:37:20 +0200 skrev Marko Mäkelä
<msmakela@gmail.com>:
> On Wed, Nov 08, 2017 at 11:01:29PM +0000, smf wrote:
> >On 08/11/2017 18:06, David Holz wrote:
> >
> >>On writing to 00/01, the 6510 enables a Write on the bus but
> >>doesn't assert the data pins. In the C64, the net effect is that
> >>the lingering prior data value from the VIC-II's bus phase will get
> >>written to those RAM locations.
> >
> >Does it have the same reliability issues to running code in
> >de00/df00 from vic fetches, which vary by motherboard capacitance
> >and temperature.
> 
> I expect so. BTW, this question was asked here only a few weeks ago,
> and if I remember correctly, in reply to my reply, Groepaz posted a
> link to his test program that writes and reads the memory locations 0
> and 1.
> 
> Also, on the C128 (not B128 aka 600/700 series) it is trivial to read 
> and write these locations via the addresses $100 and $101 after 
> redirecting the stack page with the MMU.

The Z80 would also probably be a simple way to read those addresses.

In this way, and by not using $0/$1 from the CPU, it would be possible
to have one more sprite or one more screen in the 0-$3FFF area :)

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