[Coco] Grr!!! Bad MPI! No biscuit!

[Joel Ewy]

Gene Heskett wrote:
> On Saturday 05 May 2007, Joel Ewy wrote:
>   
>> Jim Cox wrote:
>>     
>>> I have a MPI board that someone gave me.  I am not sure if it works or
>>> not, but it's yours.
>>>
>>> Jim
>>> PS: We need a new MPI for the CoCo
>>>       
>> Here's a humble suggestion for anyone contemplating such a thing:
>> Orient the board perpendicular to the desktop so that any cartridges
>> plugged into it will be parallel with the desktop.  Having the disk
>> controller stick up 8.5" from the surface of the desk is just a bit silly.
>>
>> As much as I loathe trying to find places to plug them all in, maybe an
>> external transformer would be a good idea here...
>>     
>> Would it be feasible to put bi-directional bus drivers in a short
>> cartridge and connect the CoCo to the MPI via a short length of ribbon
>> cable?  That would provide much greater flexibility in placement, and
>> probably reduce the chances of bumping things out of place.
>>
>> JCE
>>     
>
> This idea falls over due to a bus contention in the mpi's internal timing, 
> which in turn causes a ground bounce that is only barely tolerable if the 
> grounding ear clips in the side port have a good clean grip on the mpi's 
> ground plane.  Additional jumpers of heavy wire to tie the mpi's rather 
> surpentine ground plane together also help, as does additional bypassing near 
> the ls245.  You can make it stable, as shipped, its a house of cards.
>  
>   
Are you saying that this problem is intrinsic to any CoCo multi-pak
design, or just Rad Shak's?  FWIW, I'm musing about a possible future
product, not modifications to the existing design.

JCE
>>> On Sat, 5 May 2007 03:12:01 -0600
>>>
>>>  Willard Goosey <goosey at virgo.sdc.org> wrote:
>>>       
>>>> My old-style MPI is apparently toast.  My CoCo has therefore lost
>>>> access to its hard drive.  :-(
>>>>
>>>> I suspect power supply problems.  Either that or the upgrade PAL is
>>>> loosing its mind.
>>>>
>>>> Just what I need, something else broken.
>>>> Willard
>>>> --
>>>> Willard Goosey  goosey at sdc.org
>>>> Socorro, New Mexico, USA
>>>> "I've never been to Contempt!  Isn't that somewhere in New Mexico?"
>>>>   --- Yacko
>>>>
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