[Coco] [COCO] Stacking the 6309?

[William Astle]

I think you've reversed the intent of the "why bother" question. I take 
it to mean "why bother keeping the 6809 because by default the 6309 
works the same", not "why bother with a 6309".

For software the behaves and doesn't rely on undocumented 6809 
behaviour, there is no need to keep the 6809 around. The 6309 in 
"emulation" (default) mode will work the same.

There is, however, some software out there that relies on undocumented 
behaviour such as the code sequence "$10 $20" being executed as "LBRA" 
even though that is not officially documented anywhere and any proper 
software won't do that. For things relying on undocumented behaviour, 
you need a real 6809 to make them work properly. Fortunately, such 
software is rare since most assemblers won't output such bad code.

Also, as noted elsewhere, if you want to be absolutely certain something 
you're building works properly on a real 6809 (making sure you didn't 
get some stray 6309-only instructions mixed in, for instance), running 
it on a real 6809 is useful.

On 2017-03-31 09:57 AM, Salvador Garcia via Coco wrote:
> There is software that takes advantage of the 6309's enhanced features that are not available in the 6809. Additionally, some (all?) of the 6309's instructions are optimized, so they run a tad bit faster than in the 6809. If for no other reason, the 6309 can provide a slight speed boost. I've read here that a 10% increase in speed is realistic. Salvador
>
>
>       From: Bruce W. Calkins <brucewcalkins at charter.net>
>  To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
>  Sent: Thursday, March 30, 2017 8:52 PM
>  Subject: Re: [Coco] [COCO] Stacking the 6309?
>
> Since the 6309 normally works like a 6809, why bother?
>
> Bruce W.
>
>
>
> On 03/30/2017 05:59 PM, S Klammer wrote:
>> A while back, we had some discussion about using a ZIF type socket to allow
>> swapping back to a straight 6809.
>>
>> Seems Chris Burke (of Burke & Burke) provided some instruction on just
>> stacking the 6309 on top of the existing 6809, along with a switch...
>>
>> http://www.6809.org.uk/dragon/6309fit.shtml
>>
>> Shain
>>
>
>