[Coco] Re: 64K Mode

[jdaggett at gate.net]

What ever.

Correct I shorted the upper range 16 bytes. $FFF0 is the start of 
I/O. The Ram is switched in two banks and are located between 
$0000 and $7FFF when memory map type 0 is selected. 

The HD63x09 has vector for illegal opcode trap at $FFF0 and 
$FFF1. The MC68x09 does not. 

james

On 13 Jan 2004 at 18:04, Alex wrote:

From:           	Theodore (Alex) Evans 
<alxevans at concentric.net>
Subject:        	Re: [Coco] Re: 64K Mode
Date sent:      	Tue, 13 Jan 2004 18:04:41 -1000
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> 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
> 
> 
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