[Coco] Checking/Testing a 68B09P

[jdaggett at gate.net]

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