Simple DIY I/O Cart

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Door zPasi

Champion (438)

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06-03-2019, 19:46

It's not very difficult to make a simple i/o device for MSX cartridge port.

I made this simple breadboard thing that reacts to OUT 81h by switching a LED on/off.

Video: https://youtu.be/jBcHAz7ioYE

It looks kinda wild, but works. At least long enough to shoot that video :)

Actually it's so simple that also IN lights up the LED, because even WR is not connected. IORQ and A0 - A7 are.

Even that simple a device could be used to control up to 8 relays, etc

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Van roadfighter

Champion (388)

afbeelding van roadfighter

07-03-2019, 03:11

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

Van Grauw

Ascended (8368)

afbeelding van Grauw

07-03-2019, 09:18

Contrary to the printer port though, I think this set-up is also a good learning experience towards more complicated cartridge designs. I'll give it a try as well!

Van zPasi

Champion (438)

afbeelding van zPasi

07-03-2019, 09:32

roadfighter wrote:

You could use the printer port for this, mutch easier and available on any msx.

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.

Van NYYRIKKI

Enlighted (5357)

afbeelding van NYYRIKKI

07-03-2019, 09:52

Usually when people do things like this they select Intel 8255 chip, but it seems you have selected another approach... I must say it looks cool experiment!

Van zPasi

Champion (438)

afbeelding van zPasi

07-03-2019, 10:49

NYYRIKKI wrote:

Usually when people do things like this they select Intel 8255 chip, but it seems you have selected another approach...

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 Smile

Quote:

I must say it looks cool experiment!

Thanx!

Van NYYRIKKI

Enlighted (5357)

afbeelding van NYYRIKKI

07-03-2019, 12:21

zPasi wrote:

Yeah, the good old 8255. Maybe I'll study that chip later.
Can 8255 be used for address decoding?

It is quite easy to study as it is already included inside MSX to handle stuff like memory mapping, keyboard and cassette output. 8255 has /WR, /RD, /CE, A0 and A1 implemented. Rest of the address decoding you have to do your self with NAND or something.

See here for details:
https://en.wikipedia.org/wiki/Intel_8255

Van Wlcracks

Champion (321)

afbeelding van Wlcracks

07-03-2019, 16:49

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

Van zPasi

Champion (438)

afbeelding van zPasi

07-03-2019, 17:32

Wlcracks wrote:

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

Not yet, but I'll put up something.

Van NYYRIKKI

Enlighted (5357)

afbeelding van NYYRIKKI

07-03-2019, 19:07

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

Van thalin

Rookie (19)

afbeelding van thalin

07-03-2019, 19:09

Cool! I hope to start playing with a cartridge soon. Just got some prototyping cartridge PCBs.

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