[Coco] Upgrade MPI?

Barry Nelson barry.nelson at amobiledevice.com
Thu May 7 03:53:58 EDT 2015

It's not a software issue, it's HARDWARE. A non upgraded MPI on a CoCo 3 attempts to output conflicting voltage levels at the same time as the GIME chip when certain registers are read. This effectively causes a short circuit as one chip attempts to output 5V and the other chip tries to pull the line to 0V. This happens for a very short time, but if the right conditions are met, the GIME chip CAN be fried. If you care about the CoCo 3 and want it to last DO NOT use an un-upgraded MPI with a CoCo 3! It can fry the GIME. The is an upgrade you can apply that does not require a programmed pal ship, just a single 74LS10 chip and a few wires. Here is a link.


DO NOT use it on the the CoCo3 without upgrading it! The 74LS10 chip is a standard part and is readily available.

FYI: I have used this upgrade on a MPI I own and in addition to working correctly on the CoCo 3, I am still able to use it on my CoCo 1 as well.

On May 6, 2015, at 8:47 PM, coco-request at maltedmedia.com wrote:

> Date: Wed, 06 May 2015 20:38:49 -0400
> From: Robert Gault <robert.gault at att.net>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] Upgrade MPI?
> Message-ID: <554AB419.9010606 at att.net>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> K. Pruitt wrote:
>> <snip>
>> By the way, I'm not trying to be a smart aleck.  I'd really like to know.  I
>> remember reading an article by, I believe, Marty Goodman, about the PAL.  He
>> definitely stressed having the MPI upgraded, but I only recall him emphasizing
>> program corruption and data loss, not hardware damage.  Of course it's been 25
>> years or so since I read it, so I could be remembering incorrectly.
> I don't think there is any way that you could damage a Coco (any model) with 
> software. If your MPI works with your Coco3 without problems, great. Don't 
> change anything.
> I'm not sure which if any MPI worked with a Coco3, so I may be off on your model 
> number.
> Robert

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