From: David Wood (jbevren_at_starbase.globalpc.net)
Date: 2004-03-18 08:04:43
(replies mixed with text)
On Thu, 18 Mar 2004 ncoplin@orbeng.com wrote:
> Hi Guys,
>
> >_dW and I were discussing how the SCPU changes the built-in IO port on the
> >6510, and werent able to come up with an explanation. Anyone here have any
> >theories that can be tested?
>
> I think Marko mentioned it once before on this thread. The theory is that
> when the "cart" boots in EXROM mode (running the 6510) it writes to 0/1 to
> put the CHARROM into view, then swaps over to running the external 65816.
I can verify that it boots using exrom (game actually, at $8000). I
discovered this accidentally while working on an external psu mod for my
c64c's cart port. The c64 would come up 8k short and tapping restore would
start the scpu.
> >From then on, writes to $D000-DFFF go under ROM to the RAM. The GAME line is
> pulled low (Ultimax mode) to bring the I/O map into view for writing to IO.
> As the SuperCPU mirrors the RAM writes, all reads from this area come from
> its own external copy of the RAM.
Hm sounds feasable. I'll dig up the abel source for the pla and see if
that'd work.
>
> Hope I got the description right, Marko?
>
> - Nick
>
>
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