[Coco] [!! SPAM] Re: 6809 / General CPU question

[John Kent]

I suspect the vector is read into a temporary internal register then 
transferred to the program counter as the program counter is used to 
fetch the vector or at least it can be. The program counter would have 
to be pre-initialized with all 1's in the high address bits and a 
interrupt vector offset in address bits A3 to A1 on reset. I don't know 
if that is how Motorola did it. I was a bit concerned about patents, but 
I think they have all expired, so I don't think I'm violating anyone's 
patent. I'm certainly not making any money out of it.

John.


On 20/02/2011 10:46 AM, Mike Rowen wrote:
> Thanks everyone for your responses. Ok, so whenever the CPU powers on 
> or experiences a RESET inturrupt, the CPU will read the contents of 
> FFFE & FFFF and load it into the program counter register. It then 
> fetches instructions from that location. Presumably this would be a 
> location in ROM.
>
> How does an address get into FFFE & FFFF when the system is 
> initialized? Is this through hardware? Are these RAM locations?
>

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