[Coco] Why do we need a CoCo 4? (Long irrelevant rant)

[jdaggett at gate.net]

On 30 Dec 2008 at 20:14, Joel Ewy wrote:

> Frank Swygert wrote:
> > Am I reading this right? Could a more or less CoCo compatible
> > machine be made with a HC12? Something that would be at least 75%
> > compatible? 
> Not quite Frank.  The issue here is that the HC12 lacks the U(ser)
> stack pointer register.  That's a pretty major omission. (Nitr)OS-9
> would be right out, and I suspect that DECB uses U as well.  It's an
> "if only", but a pretty big "if only".
> 
> JCE

Joel

That is what I said. if the HC12 had the U pointer register then it would be 
the CPU for the next Coco. Infact I told one of the managers of the HC11 
line that one the HC11's biggest defects was  it lacked that U pointer 
register and he agreed with me. 

The HC12 is about 80% source code compatible. Object code is not 
compatible. 6809 code would have to be reassembled. You do have to deal 
with the PSH*/PUL*  instructions.

james