[Coco] grey MPI 26-3024 - how to tell if upgraded

[RETRO Innovations]

Not sure if this made it or not, so resending.  Apologies if dupe:

On 2/1/2015 4:44 PM, Darren A wrote:
> On Sun, Feb 1, 2015 at 2:52 PM, RETRO Innovations wrote:
>
>> So, is there a link to a note that explains why the PAL changes were not
>> backward compatible? As I understand it, the Coco3 MPI PAL allows
>> addressing only ff7f, but the earlier MPIs would allow ghost locations.
>> Why would disallowing the ghost make the unit not usable with Coco 1 and 2
>> machines?
>>
>>
> I have never experienced any problem using my upgraded 26-3024 MPI on a
> CoCo 1 or 2.
>
> The PAL upgrade does not just affect ghosting of FF7F.  It causes all
> addresses from FF80-FFBF to be excluded so that the data bus transceiever
> is not activated when you read from that area.  Before the CoCo 3 those
> were legitimate addresses for external hardware. The GIME took over that
> range so the MPI must leave the data bus tri-stated when reading from there
> to avoid contention.
>
> - Darren
>
Is there anyone who can confirm the below?  THere are a few 
discrepencies (on CTS, for example, and no mention is made if SLENB 
writes are allowed)

  * If SLENB active
      o allow reads from any location
      o allow writes from any location?
  * If SCS active (Coco3SM says this is only active for both reads and
    writes, but only for addresses ff40 to ff5f)
      o allow reads from ff40 to ff5f
      o allow writes from ff40 to ff5f
  * if CTS active (Coco3SM says this signal is only asserted on reads
    from c000 to dfff, but Gunnison's doc says c000 to feff)
      o allow reads from c000 to dff (feff?)
  * If no additions lines active:
      o allow read from ff40-ff7f
      o allow writes from ff40-ff7f

The PLD equations 
(http://www.coco3.com/community/2010/06/26-3124-mpi-coco-3-upgrade-2/) 
seem to say:

enable buffer if:

  * address is $ff40-$ff7f or (regardless of whether SCS is active or not)
  * SLENB is active (any address) or
  * CTS is active (any address)


What about ff80-ff8f?  Why can't it be used?


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