[Coco] MPI mod for coco3

[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.
>