[Coco] [Color Computer] Hardware specifics regarding GIME , RAM and ROM

[jdaggett at gate.net]

The Coco3 does not use the internal ROM. It is copied to RAm and patched 
to work with the Coco3 system. Cartridge ROMs are the only ROMs read 
and are mapped between $C000 and either $FFDF or $FFEF.

james


On 30 Apr 2009 at 0:26, Arthur Flexser wrote:

> On 4/30/09, news at wzydhek.com <news at wzydhek.com> wrote:
> >
> >
> >  > -----Original Message-----
> >  > From: ColorComputer at yahoogroups.com
> >  > [mailto:ColorComputer at yahoogroups.com] On Behalf Of Mike Pepe
> >  > Sent: Wednesday, April 29, 2009 11:15 PM To:
> >  > ColorComputer at yahoogroups.com Subject: RE: [Color Computer]
> >  > Hardware specifics regarding GIME , RAM and ROM
> >  >
> >  > > I have a few questions regarding the GIME, RAM and ROM.
> >  > >
> >  > > 1) If I understant what I have read so far, if $FFDE is written
> >  > > to, then the memory will be in ROM mode, meaning $8000-$FEFF
> >  > > will be
> >  > accessed from
> >  > > rom?
> >  > > How does the MMU registers $FFA0-$FFAF affect this? Can those
> >  > > ROM addresses be remapped to different memory slots? (Instead
> >  > > of $8000 being at $78000, can it be read from the equivalent of
> >  > > $18000, etc?)
> >  >
> >  > No, the MMU affects RAM only.
> >  >
> >
> 
> Actually, that's incorrect, though the ROM segments respond in a
> different way to changing the MMU values than RAM segments do.  We had
> a thread about this a while back.  Particular ROM segments can only be
> moved to certain addresses, and what address you pick determines which
> ROM segment moves there.  You can even move segments from the internal
> patcher ROM, which is normally inaccessible, to locations where you
> can see them.  It works in a very weird way.
> 
> Here's part of a message I posted to the list back in April of '04
> that gives details:
> 
> Here's what happens as a result of moving ROM segments around,
> according to some old notes I dug up, where all MMU pokes
> are done in ROM mode:
> 
> MMU location    Value          Segment moved                
> Destination
> 
> $FFA0        $3C or $3D      I0  ($8000 Extend. Bas.)           $0000
>                     $3E or $3F      E0  ($C000 External ROM)
> 
> $FFA1         $3C or $3D      I1  ($A000 Color Bas.)             
> $2000
>                      $3E or $3F      E1  ($E000 External ROM)
> 
> $FFA2        $3C or $3D      I2  ($C000 Int. Basic patcher)   $4000
>                     $3E or $3F      E0  ($C000 External ROM)
> 
> $FFA3        $3C or $3D      I3  ($E000 Int. Basic patcher)    $6000
>                     $3E or $3F      E1  ($E000 External ROM)
> 
> 
> I haven't actually verified the $FFA0 results, but inferred them from
> the pattern of the others.:
> 
> 
> 
> Art
> 
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