[Coco] Multipack info

[Gene Heskett]

On Friday 29 September 2006 18:03, Bruce W. Calkins wrote:
>> This is the first I have heard of this. Must be that someone used the
>> reserved location for something they shouldn't have.......

Unk Bruce, I assume that somewhere, someone may have designed a cartridge 
that used the $FF7F adress for something other than the MPI's slot 
control.  But I've not found such a beast in my wanderings.

To clarify why the mpi needs to be fixed for the coco3, note that the mpi's 
original address decoder also had a response to $FF9F writes, and in the 
coco3, thats a gime register, so updating the gimes memory mapping during 
a context switch (os9 only) fiddled with the slot latches in the MPI.  The 
fix is to disable that false response with the 74LS10.  Or use a remapped 
pal decoder chip in the earlier 3024's.

Note that while you've got the thing open, one should jumper all 4 sockets 
together at pin 8, and then remove 3 of the 4 individual IRQ pullup 
resistors along the front of the board.  This takes care of the infamous 
'missed interrupts' when using the mpi.  They play all sorts of tricks 
with your data when you are online with the coco, very effectively killing 
zmodem.  So fix that while you are in there.

>Are you referring to the switch or the tales of flakey CoCo 1/2s with the
>upgraded Multi-Pac interface?  Unfortunately with all the computer
> crashes I've recovered from, I still have files in need of recovery and
> resorting. I can't quote a source on the flakey CoCo 1/2 on a upgraded
> MPI at the moment.  It might be just a "understanding"?
>
>I know I did find a description for a switch for this once.  It would
> seem simple, given what little I needed to do to install the upgrade in
> my 26-3124.  Certainly not as hard as the "simple" TTL detector I need
> to design for class Tuesday to flag illegal BCD values.  ;)
>
>Bruce W.
>
>> Rule Number 1: Foolow the spec if there is one.....In this case there
>> was......
>>
>> If you find it, I would love to read it.
>>
>> Thanks,
>>
>> Mark
>>
>> Quoting "Bruce W. Calkins" <brucecalkins at bellsouth.net>:
>> > Stock, it works well with the CoCo 1 and 2.
>> > To use it with the CoCo3 it needs a addressing modification.  Not
>> > hard,
>
>just
>
>> > a 74LS10 IIRCC with some short wires and a trace cut.  Unfortunately
>
>this
>
>> > makes it flakey with the CoCo 1 and 2.  Somewhere on-line somebody
>> > wrote
>
>up
>
>> > a modification that allowed a switch, so you could swap it back and
>
>forth.
>
>> > Bruce W.
>> >
>> >> I am getting back to using  my coco3. I have a Tandy Multi-Pack 
>> >> Model 26-3124 S/N 2007430.
>> >>
>> >> Will this unit work with the coco2 or coco3 without causing damage?
>> >>
>> >> Thanks
>> >>
>> >> John Chasteen

-- 
Cheers, Gene
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.