[Coco] Re: 64K Mode

[Theodore Evans (Alex)]

On Jan 13, 2004, at 3:39 PM, jdaggett at gate.net wrote:

> The Sam Chip in the Sam Chip of the CoCo 1/2 hasa two memeory map types
>
> Type 0 is ram from $0000 to $7FFF and Rom from $8000 to $FDFF and from
> $FFF2 to $FFFF.  $FF00 to $FFDF is I/O and $FFE0 to $FFF1 unused.
>
> Type 1 is all ram $0000 to $FDFF. $FF00 to $FFDF is I/O and $FFE0 to 
> $FFF1
> unused. $FFF2 to $FFFF is ROM and vector location.

I am almost positive that the the area switched extends up to $FEFF 
with only 256 bytes for I/O and vectors.  In fact according to some 
notes that I made a long time ago the destinations for the all but one 
of the 6809 vectors (I don't have a note for the 6309 unimplemented 
instruction at $FFF0) lie in in the FE00-$FEFF range.  SWI3 pointing to 
$FEEE, SWI2 to $FEF1, FIRQ to $FEF4, IRQ to $FEF7, SWI1 to $FEFA, and 
NMI to $FEFD with reset being the exception which points to $8C1B