Simple DIY I/O Cart

You could use the printer port for this, mutch easier and available on any msx.
Out &H91,x for the data lines.
But nice go, always nice to see new msx hardware. Simple or hard it doesn't matter.
Greets,

Emil

Not available on any MSX. Probably should be, but not on every model.

There is also other reasons one would want to use cart slot. Depends what you'll want to achieve. But you're right, (for simple applications) the printer port is one option.

Yeah, the good old 8255. Maybe I'll study that chip later.

My "design" just uses 74xx02 (NOR) and 74xx00 (8 bit NAND) for address (+ IORQ) decoding. The third chip is a 373 used for latch, might use some other chip, or an Arduino (!) instead.

Can 8255 be used for address decoding?

I also use CPLDs but they tend to be literally ... complex

Thanx!

Cool, is there a schematic available? Even on a bierviltje, just to get an idea?

BTW if you want to see 8255 implementation on a cartridge, take a look ie. BEER IDE that implements IDE-bus with this chip... or Sony HBI-55 that is very similar device, but connects the GPIO pins to SRAM chip instead of IDE-device... I remember there was also very detailed article of building EPROM programmer using 8255 in MSX MAGAZINE issues 07/1990 - 02/1991