[Coco] Interrupt Vectors Physical Location ???

[William Astle]

On the Coco1/2, it does come from the top of the Color Basic ROM (BFFx). 
On the Coco3, it comes from the top of the internal 32K ROM which would 
be at FFFx naturally if not for the I/O area.

I think the mapping is handled by the SAM (Coco1/2) or GIME (Coco3). 
There may be other logic involved as well.

So the hardware you need to replace is, in fact, the relevant ROM.

Note that FFF0/1 also come from the same area which may be relevant if 
you're using a 6309.

On 2019-12-28 3:01 p.m., M. David Johnson wrote:
> $FFF2 through $FFFF provide the CoCo's interrupt vectors, i.e. RESET, IRQ, SWI2, etc.
> 
> Since these can't be changed, and are present the moment you turn the CoCo on, I'm guessing they're in ROM.
> 
> But, physically where??
> 
> I don't think they can be in any of the 8K ROM chips because none of those reach the $FFF2 address (although the BASIC ROM mirrors the vectors in $BFF2 through $BFFF).
> 
> For example, if I wanted to jump to $0000 on startup instead of to $A027 or $8C1B, which piece of hardware would I need to remove and replace?
> 
> I've gone through the Unravelled books and the Technical Reference Manual. Am I perhaps just missing something?
> 
> --
> M. David Johnson
> mdj at bds-soft.com
> 
>