[Coco] 6309/6809 opcodes with mixed 8/16 bit registers

[William Astle]

On 12-11-22 09:55 PM, Mike Pepe wrote:
> I could have sworn the HCF on the 6809 was $FF. I recall that if you were to
> take a 6809, stick it on a breadboard, give it power and clock it'll run the
> address bus test routine- the data bus should float to $FF if it's not
> connected...
>
> Hm, I should (re?) try that. I'm certain I've done this before.

$FF is STU extended so it's definitely not HCF.