[Coco] Color Computer 2 and MPI

[Barry Nelson]

> Bruce W. Calkins 
> Sat Apr 14 08:07:48 EDT 2018
> 
> My understanding is that there are some conflicts with the upgraded MPI 
> and the CoCo 1 & 2.  There was a hack for piggybacking the GAL/PAL chips 
> for interchangeable use with the older MPI.
> Bruce
> w.
The problem in the CoCo 3 with an unmodified Multi-pak is that any attempts to read or write to addresses in the range of $FF90 to $FF9F result in both the CoCo 3 GIME chip and the Multi-pak slot controller chip both responding. The modification prevents the MPI and any devices plugged into it from responding to any addresses in the range of $FF80 through $FF9F. Very few devices use those address ranges even on a CoCo 1 so unless you try to use one of the very few devices (cartridges) addressed in this range, the Multi-pak will work fine. If you do attempt to use a device in the $FF80 to $FF9F range, it will simply not respond and no harm will occur. So the bottom line is that yes, you can safely use a CoCo 3 patched Multi-pak on a CoCo 1 or 2 and it will generally work just fine.