[Coco] Cartridge memory - mapping in and out

Arthur Flexser flexser at fiu.edu
Mon Oct 29 17:48:20 EDT 2007

On Mon, 29 Oct 2007, Roger Taylor wrote:

> (On a CoCo 3) I think doing a POKE 65502,x from BASIC is a no-no 
> because it switches out the patched ROMs (which are in RAM) and 
> switches in the underlying actual ROMs, and performing any commands 
> now could crash the system.
> That's what the EXEC $E010 does,... very quickly by machine language 
> - sets up the GIME and RAM/ROM switch to prepare to run the cartridge 
> ROM without letting the user fiddle around at the prompt or perform 
> any other functions.

This is not actually true, Roger.  The CoCo 3 patches were carefully designed to
avoid such a crash, for compatibility with existing programs.  The only thing
is, you can't do the ROM poke from the 40/80 column screen, since the screen
drivers for that are in the Super Extended Basic RAM that will be switched out.  
(I don't recall whether you can still type blind if you do the poke from a 40/80
column screen, or if the CoCo just crashes in that case.)


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