ncoplin_at_orbeng.com
Date: 2004-03-18 02:43:48
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.
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.
Hope I got the description right, Marko?
- Nick
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