Re: PC-card (4)
Date: 2001-04-13 15:23:39

On Thu, 12 Apr 101 wrote:

> Hallo David, Nicolas,
> > > I think, if you enable Ultimax mode, there is no RAM that can be 
> > written to.
> > > This way you can use about every memory location above $1000 to map in 
> > your
> > > own I/O. I just wonder if the SCPU is compatible with this mode.
> > 
> > After _very_ careful interpretation of the PLA's reverse-engineered
> > sourcecode, Bogax and I have decided that unless you're writing to the I/O
> > page, you can't not write to ram.  The only thing that throttles the WE 
> > line
> > on the internal dram is the I/O outputs on the PLA
> The only thing I know, and even that could be wrong, is that Ultimax is a 
> "way" to replace the Kernal with an external one.

The AR cart does it some way  I cant particulary remember in mu just-woke-up
state. ;)  They do it this way so they can acess all the ram in the c64 and
copy some of it to offboard ram(?) so that it can do its debugging/freezing

Umax mode is  a relic mode from the Ultimax game system based on the c-64. 
This machine had 2k of static ram and a simpler pla, as well as a slightly
different vicII (no ram refresh), a single CIA for the joyports, and a
cartridge port.  The umax mode on the c64 emulates this memory map, plus
tyhe 2k of extra ram on the game cart, if present.

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