[Coco] Checking/Testing a 68B09P

[Frank Pittel]

On Mon, Jul 02, 2007 at 08:39:38AM -0700, Mike Pepe wrote:
> jdaggett at gate.net wrote:
> >On 1 Jul 2007 at 20:38, Mike Pepe wrote:
> >
> >>jdaggett at gate.net wrote:
> >>
> >>>Pins 33 through 39 are different between the MC/HD68B09 and the
> >>>MC/HD68B09E. The differences are significant that would require
> >>>major rewireing of the COco motherboards to use a MC/HD68B09. 
> >>Er... what?
> >>
> >>No amount of rewiring will get a 68x09 to run in a CoCo. Rigging up
> >>some sort of contraption to get the clocks synchronized may be
> >>possible, but I wouldn't recommend it!
> >>
> >******************
> >
> >I beg to differ. I would agree that there is no real easy solution but 
> >there are some. One can be to feed the E clock  to a PLL that multiplies 
> >the clock four times and feed that to the MC68B09 EXTAL pin. Then you can 
> >slave the MPU off any Coco. The pins on the MC6809E like LIC, BUSY, and 
> >AVMA are not used on the Coco 3 and are floating. You leave the MRDY and 
> >DMA lines tied high and float the E and Q lines on the MC68B09 and plug 
> >the adaptor into a Coco. 
> >
> >You can also tap off the 14.3 or 28.6 MHz crystal buffer it and divide 
> >down if needed but then if you switch speeds then you have an issue. The 
> >best method is to do as above and  it will work. 
> >
> >james
> >
> 
> Well, it's not your method I found confusing, just your semantics.
> 
> "Rewire" implies taking existing signals and feeding them to different 
> places and it magically works, which as you know is in this case, 
> impossible.
> 
> Building a PLL and circuit to synchronize the E/Q clock from the SAM to 
> a non-E 6809 is indeed possible- but that to me is a bit more than a 
> simple rewire job!

Other then doing it because you can. Is there a reason why a person
would want to build an interface to allow the use of a MC68B09 in a
Coco? The cost of building such an interface must certainly exceed the
cost of an "off the shelf" chip that could be used without any
modification.

This is a serious question.

Frank