[Coco] Upgrade MPI?

Salvador Garcia ssalvadorgarcia at netscape.net
Thu May 7 10:15:30 EDT 2015

The uncertainty with this type of issue is whether it will cause actual damage. Fact is, it is not 500mA going through those lines so the CoCo3 won't go out in a blaze of glory. Since the current is minimal there is that chance hat the short will not fry the GIME. But... of course there is a but... if a perfect storm is created then damage can occur. What this means is that CoCo 3 #12999 might live a long and fruitful life alongside an un-upgraded MPI and never feel the heat while CoCo 3 #14778 might get jolted into a parallel universe right after the MPI is connected to it. The question here is: Which of these two CoCo 3s do I own? As a wise man once asked: Do you feel lucky punk? :-)


-----Original Message-----
From: Joe Grubbs <jsgrubbs at hotmail.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Thu, May 7, 2015 8:54 am
Subject: Re: [Coco] Upgrade MPI?

I knew of the address overlap and potential software crashes that could occur,
but this is the first I've heard of actual hardware failure. I wonder if this is
theory, conjecture, or if it has actually happened to people?

Either way I'll
likely continue to use my modified 26-3024 with the CoCo3 and reserve this one
for one of my CoCo2s. 

Speaking of which, I noticed that the selector switch on
this 26-3124 is detented, whereas the one on my 26-3024 has no significant
detents. I just figured they were all like that. Is my 26-3024 actually broken
and I've just never known?

> From: barry.nelson at amobiledevice.com
> Date:
Thu, 7 May 2015 03:53:58 -0400
> To: coco at maltedmedia.com
> Subject: Re: [Coco]
Upgrade MPI?
> 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.
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.


Coco mailing
Coco at maltedmedia.com


More information about the Coco mailing list