[Coco] Re: Any reason to put a 6309 in a Coco2?

[Theodore Evans (Alex)]

On Dec 31, 2003, at 12:48 PM, Gene Heskett wrote:

> I've always been told that for those intructions where it was doing
> something internally, and the 6809 didn't use its bus cycle, that the
> 6309 took advantage of the spare bus cycle and fetched the first byte
> at least, of the next instruction.  Is this incorrect, and it still
> has to not only fetch, but then decode the next instruction at all
> times?
>
> This is, ISTR from data supplied at the time by Chris Burke and Chet
> Simpson, each of whom published their versions of the new opcode maps
> complete with timing info for each command.

This is how the 6309 works in 6309 mode, but in 6809 mode it waits so 
that  he cycle timing is the same.  The 6309 was supposed to simply be 
a CMOS version of the 6809.  All of the extra 6309 stuff was secretly 
put in by the engineers on the project.  Officially Hitachi knows 
nothing about there being any functional differences.  AFAIK that this 
is what was put out when talk about the 6309 first broke out on the 
CoCo list.