[Coco] Checking/Testing a 68B09P

[Mike Pepe]

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!