Re: 65816 and I/O

From: Marko Mäkelä (
Date: 2001-01-22 17:43:53

On Mon, 22 Jan 2001, Nicolas Welte wrote:

> I'm not sure, but doesn't the Ultimax mode have the I/O always switched
> in, even if the processor port for C64 operation is set to an all-RAM
> configuration?

Yes, that's it.  Just program the 6510 to "I/O area off" (RAM or character
generator ROM at $d000, it doesn't matter, since writes get "through" the
ROM), and pull -GAME low when you want to access the I/O area.

> But I remember that they had a real problem supporting the ASCII/DIN or
> ASC/CC key on international C128 machines, because this key can only be read
> through the processor port. Don't know how they solved this, because only the
> 8502 can read that bit. Probably they switch back to the 8502 to read it.

Don't they use an MMU adapter socket anyway in the C128?  The CAPS LOCK
key (I guess it is important also for non-localised units) could be wired
to an I/O line on the SuperCPU cartridge.  That is not a big internal


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