22 March 2018



I have a Panasonic MSX2+ FS-A1FX. This model does not have FM synthesis built in. I have 3 MSX cartridges:

The Panasonic, like most MSX computers only has 2 slots... But with some of the latest games like
Myths & Dragons released, I could easily use all 3 cartridges. The GR8NET provides FM music, the V9990 provides
the graphics chip needed, and the MegaFlashROM is big enough to run the digital version of the game.

So somewhere around 2002, Hans Otten published a quick and dirty guide to building an IO Slot. Perfect for
the V9990... Hans Otten - slot extender

With the ease of access to China to manufacture pcboards today, I turned to KiCad, and drew up an even
simpler version. My version does not use ribbon cables or spliced wires and crimp connectors.. It is a
pcboard, that simply adds the IO Slot. Their is no switch to disable the slot select on the primary slot.

This is just an IO Slot

The first slot is a full primary slot. The second is the IO Slot.


Where to buy:


If he's out of stock, I'll make more.


  1. The expander provides about 25mm from the front of a Kanomi style cartridge to the tip of the edge connector.
    Which after insertion into the rear of the Panasonic, leaves about 2mm. So this might not be right for everyone!

  2. There is no index to force correct orientation of cartidges. Cartidges should face you as you face the keyboard,
    just as they do in the top slot of your MSX.

What is an IO Slot:

An IO Slot never receives a SLOT-SELECT signal from the MSX. Thus it cannot contain ROM or RAM for the Z80
to access directly. It can only interact with the Z80 IO Port concept that uses the lower 8 bits of the
address bus to select one of 256 ports that then communicates value over the data bus outside of normal
memory access cycles.

Sound chips, V9990 video cartridges, modems, and other devices often only used IO ports.