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Multi Pack Interface (MPI) #26-3124

PostPosted: Tue Oct 17, 2017 3:04 am
by ogsteviestrow
If you own the Multi Pack Interface, MPI unit with the model number of 26-3124 this unit is very easily upgrade-able to work with a CoCo 3.
Please be advised that using an MPI not designed for the CoCo 3 can result in frying the GIME chip which is the most important, and nearly impossible to replace part.

The upgrade requires swapping out a PAL chip that you can get from Cloud 9 technologies or Ed Snider.

You can tell if this unit has been upgraded to work with the CoCo 3 by using the following PEEK command from BASIC:

PRINT PEEK(&HFF90) and press ENTER.
If 126 is returned then the Multi-Pack has been upgraded. If it returns 255 then it has NOT been upgraded.

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Tue Oct 17, 2017 6:45 pm
by BarryN
Also, Multi Pack Interfaces with the part #26-3124A (note the letter A) should show as already having been upgraded and were upgraded by Radio Shack. I have yet to personally see one of these units.

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Tue Oct 17, 2017 7:01 pm
by BarryN
In addition to replacing the PAL chip, a Multi-Pack can be upgraded with the circuit described in this post:
First, cut the trace going to the select line, pin 19, IC2 on 26-3024 or pin 19, IC1 on 26-3124. Then attach and wire the circuit shown in the attached picture.

MPI_Mod_for_coco3.JPG
MPI upgrade schematic

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Tue Oct 17, 2017 7:53 pm
by ogsteviestrow
Thanks for the value added information Barry! :D

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Wed Oct 25, 2017 4:48 pm
by fiscap
I believe the 26-3124 MPI requires the 74LS10 (triple three-input NAND gate) upgrade to make it compatible/safe for CoCo3 use where the 26-3024 upgrade is the simpler of the two with just the PAL swap.

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Wed Oct 25, 2017 8:25 pm
by frozenbeefpie
fiscap wrote:I believe the 26-3124 MPI requires the 74LS10 (triple three-input NAND gate) upgrade to make it compatible/safe for CoCo3 use where the 26-3024 upgrade is the simpler of the two with just the PAL swap.

I just love your avatar ! Had to tell you :oops: :mrgreen:

Re: Multi Pack Interface (MPI) #26-3124

PostPosted: Mon Oct 30, 2017 11:08 am
by fiscap
fiscap wrote:I believe the 26-3124 MPI requires the 74LS10 (triple three-input NAND gate) upgrade to make it compatible/safe for CoCo3 use where the 26-3024 upgrade is the simpler of the two with just the PAL swap.


Here is the re-post of the previous image Barry had uploaded - it appears that image has become corrupted. On similar diagrams which can be found for this upgrade, some show Pins 9 & 11 reversed from this diagram. Please note that they are interchangeable for this upgrade, however soldering together Pins 11 & 12 as in this diagram is a little easier and cleaner. Also, please note that in addition to this 74LS10 circuit, you still are required to cut the trace between pin 19 of IC1 and pin 52 of IC6.

This is not an easy upgrade for beginners compared to the simple PAL swap in the 26-3024 MPI. If you have concerns about doing this yourself, please work with someone who has experience doing these upgrades or send it to Mark Marlette over at http://www.cloud9tech.com/ who can do the upgrade for a relatively inexpensive service fee.

MPI 26-3124 upgrade.png
26-3124 Multi-Pak Interface Upgrade (74LS10)