[Coco] Checking/Testing a 68B09P

[jdaggett at gate.net]

On 2 Jul 2007 at 8:39, 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!
> 
Mike

Conisdering that the Coco does not use the AVMA, BUSY,  and LIC signals from 
the MC6809E, yes the rewireing is rather simple. The differenece between the E 
and Q pins on the two are the "E" version they are inputs and the non"E" version 
they are outputs. Those two pins do not  have to be connected to the rest of the 
motherboard. In fact the "E" input from either the SAM or GIME will feed the PLL. 

Pins that differ:
                 NON E version  E Version
Pin #39    XTAL(input)        TSC(input)
Pin #38    EXTAL(outpu t)   LIC(output)
pin #36    MRDY(output)     AVMA(output)
pin #35    Q  (output)           Q (input)
pin #34    E (output)            E (output)
pin #33    DMA (input)         BUSY (output)

On the Coco 3 pin #39 is grouonded and that is okay to remain. Pin #38 is no 
conncet. Pin #36 and Pin #33 are no connects. That leaves pin #35 and #36 as 
the major issues in a rewire.

james

james