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What is the Circuit for a 16K or 32K MSX computer cartridge?

Publié : 11 déc. 2019 08:59
par AprilRose
This question is about the old MSX-1 computers. I have a game I wrote, as a ROM file, and I now want to play it on a real MSX computer by putting the game into cartridge form. The game has been tested on an MSX emulator and it works. So my question is what is the simplest circuit for building an MSX-1 16K ROM cartridge or 32K ROM cartridge (using modern easy to get components)?. I have an Atmel AT28C256 EEPROM available to use. I am asking for a 16K and 32K circuit because there are two versions of the game.
Diagram below is part of a reply to answer by Anonymous. Note you could also use the 27c256 in the 16K cartridge, but I realised after more thought, it is cheaper and easier to use the 27c128 (a related similar chip) instead of 27c256. Optionally a capacitor can be put across the power lines to the EEPROM to smooth the voltage to it.

enter image description here

The 27c256 is powered by 5v this can be obtained by using pin 45 or 47 (which are both a +5v power source) and using pin 41 or 43 (which are both ground). The +12v pin, which supplies a maximum of 50ma, can also be uses to obtain a +5v power source after using a suitable circuit to reduce the voltage to +5v (though I do not know what a suitable voltage reduction circuit will be here).

Aternatively-as shown in the Alternative circuit diagram below- (as anonymous mentions in its answer)

CE is connected to SLSTL.

OE can be connected to CS12 for a 32K cartridge

or

OE can be connected to CS2 for a 16K cartridge

enter image description here

A pull down resistor (of value 5000 ohms or more) needs to be simultaneously connected (from OE to ground) to the MSX ground.

So the OE pin is shared between ground and CS12 for the 32k cartridge , or the OE pin is shared between ground and CS2 for the 16k cartridge

The two ground wires on the MSX cartridge slot (pins 41 and 43) can be wired together to create a single ground; the two VCC wires on the MSX cartridge slot (pins 45 and 47) can be wired together to create a single Vcc; and so the circuit can be powered by these four wires (41,43,45,47) used as the two power wires that deliver 5v (at up to 300 ma).

While the circuit can likely work theoretically without the capacitor and resistor -it is preferred to use it with a capacitor and resistor so it works 100% of the time. Thus the preferred circuit is the alternative circuit diagram above. The value of the capacitor in the above circuit is between 0.05uf and 0.2 uf.

The AT28C256 flash EEPROM (https://docsbay.net/data-eeprom) has a similar enough pinout compared to the 27c256 EPROM (as far as I am aware these EPROMs do not have a direct flash equivalent), except that a few of the pins are different, so it can be used instead of the 27c256 in the both circuits above. Thus an AT28C256 can be used in place of the 27c256, in both circuits above, to make a flash based cartridge (this avoids the inconvenient possibility of using UV light to bring some 27c256 into a programmable state). So using the AT28C256, in this way, would mean wiring Vcc and WE together.