[Coco] reading the ROM on a CoCo 3

[Arthur Flexser]

As Robert said, there's nothing wrong with $E00.  You should be able to verify
that what I said works from direct mode Basic with pokes (you can savem
$C000-FDFF, then offset load it to $2000 or somewhere to inspect it with
LOADM"romcode",&H2000-&HC000 to verify that you're seeing the ROM.)  I suspect
you may be poking GIME location(s) with something inapprpriate.

Art

On Fri, 28 Jul 2006, Mike Pepe wrote:

> Oh, duh!
> 
> Forgot about the old SAM ROM/RAM switch.
> 
> Interestingly enough, when I do that, the program immediately crashes.
> 
> I'm loading the short code in $0E00, the machine has 512k. First thing 
> it does is disable the interrupts.
> 
> Soon as I sta $ffde, the machine locks up and the screen fills with crap.
> 
> maybe I need to move the code to a different location.
> 
> 
> 
> 
> Arthur Flexser wrote:
> > This is doable under BASIC by POKE&HFFDE,0, which switches in the ROMs, prior to
> > doing the read.  (You need to do this from a 32-column screen, since you'll be
> > switching out Super Extended Basic's RAM drivers for the 40/80 column screens.)
> > That will get you $C000-FDFF.  If you need $FE00-FEFF as well, there's a bit in
> > one of the GIME registers ($FF90? $FF91?) that enables you to switch off "always
> > RAM at $FE00" mode, though you probably need to disable the IRQ first to avoid a
> > crash (POKE &HFF03,&H34), since you'll be switching out interrupt vectors.
> > 
> > Art
> > 
> > On Thu, 27 Jul 2006, Mike Pepe wrote:
> > 
> >> Hi guys,
> >>
> >> Does anyone know how to read the cartridge ROM directly on a CoCo 3?
> >>
> >> Whenever I try, I read the RAM copy. There is no activity on the cart's 
> >> ROM select.
> >>
> >> I tried setting $FF90 to $8C, thinking that would switch off the MMU and 
> >> go directly to the hardware, but doing reads results in nothing.
> >>
> >> The only time I get read activity on that cart select pin is after reset.
> >>
> >> What's the trick?
> >>
> >> -Mike
> >>
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> >>
> > 
> > 
> 
> 
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