Re: VIC-20 "smart" expansion port idea

From: Marko Mäkelä <>
Date: Mon, 11 Jan 2016 09:05:45 +0200
Message-ID: <20160111070545.GA9120@x220>
On Sun, Jan 10, 2016 at 03:57:23PM -0600, Jim Brain wrote:
>I have long been intrigued by the Tandy Color Computer Multi-Pak 
>Interface (MPI), and I'd like to try my hand at creating a similar idea 
>for the VIC-20.

For the record, there already exists a dumb version of this: the 
Vic-1020 expansion chassis ("docking station").

Looking at the schematic diagram, it is pretty simple: two 74LS244 and 
one 74LS245 for buffering the address and data lines, and some logic to 
drive the direction of the 74LS245 data bus buffer.

>It seems like it would be beneficial to have some control over the 
>cartridge slot, to turn things on/off, or maybe even remap things.  I 
>was thinking of a design where:
>* 3 switches on the unit would control initial state (on/off)
>* Users could remap BLK1,2,3,5 to another blk per slot (BLK1 in SLOT 1 
>would actually trigger BLK2, allowing 2 8k RAM expansion to make a
>16kB RAM
>* Users could unmap portions of IO2 or IO3 per slot (effectively fully 
>decoding IO2 so multiple carts at IO2 base could share the space).
>Yes, probably of limited utility, but I thought it would be interesting 
>to see whether it could be done.

Isn't this whole hobby of limited utility? How many cartridges are there 
that use I/O2 or I/O3 for something? That is a genuine question; I would 
like to see a list.

A pragmatic answer could be that a single flash+RAM cartridge would 
cover most needs. The main question seems to be how to use such a 
mega-cartridge together with I/O expansion cartridges. A purist answer 
is that of course you would want some way to plug in multiple original 
ROM cartridges at a time and select which one to play.


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Received on 2016-01-11 08:00:09

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