[Coco] reading the ROM on a CoCo 3

[Arthur Flexser]

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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