From: Spiro Trikaliotis (ml-cbmhackers_at_trikaliotis.net)
Date: 2008-11-28 20:25:23
Hello Marko,
* On Fri, Nov 28, 2008 at 02:32:02PM +0200 Marko Mäkelä wrote:
> On Fri, Nov 28, 2008 at 06:58:08AM -0500, Bil Herd wrote:
> > Yes, the C64 and C128 have a 'max mode where most of the resources
> > like memory and ROM are disabled.
>
> Right, everyone here should know that asserting -GAME enables the Ultimax
> mode, where only the I/O chips and the low 4k RAM are mapped and the
> upper 8k addresses are mapped to -ROMH.
>
> What I meant to say is that if the "CIA" and "CIA PLA" lines are to be
> shorted on Max cartridges, it should be safe to short the corresponding
> lines in the C64 cartridge port as well. Is this the case?
On the C64, it is -IO2 and -EXROM. As long as you do not access
$DF00-$DFFF in the I/O area, it is safe: Then, -EXROM stays high (and
-GAME is already low), and we have the Ultimax configuration.
Now, when you access $DF00-$DFFF, -IO2 gets low, and thus, -EXROM goes
low, too. However, this does not change the configuration in any
important way.
Why?
With -EXROM = -GAME = 0, the KERNEL is mapped back in, and we have a 16
KB cartridge available at $8000-$BFFF (or a 8 KB one, depending on $01).
Either way, the differences are only in $E000-$FFFF and $8000-$BFFF -
anyhow, we are accessing $DF00-$DFFF, and the behaviour there remains
the same.
I must admit I have not checked all input variants of the PLA, but to
me, it seems to be safe.
Regards,
Spiro.
--
Spiro R. Trikaliotis http://opencbm.sf.net/
http://www.trikaliotis.net/ http://www.viceteam.org/
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