[Coco] MPI mod for coco3

[Bruce W. Calkins]

This is a new one for me, saved it for future reference.

I do not have the logic for the PAL/GAL chips.  I got my GAL chips from 
Marty Goodman just before he quit supplying them.

Bruce W.

================



----- Original Message ----- 

From: "Luis Fernández"

> But this modifications is for 26-3024 and no use PAL/GAL CHIPS
> http://www.reocities.com/idezilla/CoCoZilla/patchmpi.html
>> Is there documentaion on these upgrades/MODs.  Like what exactly is the 
>> logic in the PAL/GAL.


>>
>> On Mar 13, 2014, at 02:14 PM, "Bruce W. Calkins" 
>> <brucewcalkins at charter.net> wrote:
>>
>> Upgrading 26-3024 MPIs uses a PAL/GAL chip programmed for the CoCo 3's
>> addressing pattern.
>>
>> Upgrading the 26-3124 involves trace cutting and wiring in a 74LS10 chip 
>> to
>> change the addresses.
>>
>> To make a 20-3024 MPI work with both a CoCo 1/2 and a CoCo 3 requires a
>> piggybacked PAL/GAL with a switch to activate one or the other. I'm sure
>> someone can figure out some circuitry to switch the 20-3124 type MPI.
>> Neither setup is stable with the other CoCos. IE; once you upgrade to the
>> CoCo 3 address set, your CoCo 1/2 will be unreliable with that MPI.
>>
>> Bruce W.
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