[Coco] Compatible RS MPIs to Coco 3

Ed Snider zippster278 at gmail.com
Sat Dec 26 11:58:17 EST 2020

Hi Michael,

It's the 26-3024 that can be easily upgraded with the chip swap.  The chip in
question is a PAL16V8 which can be replaced with a compatible chip (PAL or GAL)
containing the upgraded logic.

https://www.youtube.com/watch?v=XfXG8SqXleM <https://www.youtube.com/watch?v=XfXG8SqXleM>

The new logic basically keeps the MPI from responding to the addresses added
in the GIME when the CC3 was introduced (not an issue on CC1/2) to avoid
bus conflicts.

- Ed

> On Dec 26, 2020, at 10:05 AM, Michael Kline via Coco <coco at maltedmedia.com> wrote:
> Hi Jeff,
> Thanks for the info. What chip do you swap out and are they available? Probably EPROM now-adays.
> Michael
> On 26/12/2020 09:46, Jeff Teunissen wrote:
>> No _unmodified_ Multi-Pak Interface is compatible with the CoCo 3. I
>> believe that there was a time when Tandy took all of the 26-3124 "new"
>> MPIs they had in their warehouse and upgraded them to work with the
>> CoCo3, resulting in 26-3124A.
>> So I guess there's one model of MPI that's CoCo3-compatible out of the
>> box, the pretty-rare 26-3124A. All other models are incompatible
>> unless modified. The old 26-3024 MPIs are pretty easy to upgrade, you
>> replace one chip with another. The upgrade to the newer 26-3124
>> version is more involved, and probably shouldn't be done unless you're
>> pretty confident with a soldering iron.
>> On Sat, Dec 26, 2020 at 10:18 AM Michael Kline via Coco
>> <coco at maltedmedia.com> wrote:

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