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


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 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.

Update: the pull down resistor is not required (see updated answer by anonymous)

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    Releasing two versions of a MSX game kinda goes against the philosophy of the MSX platform. If the full version needs 32k RAM and you want to be able to play the game on a 16k computer, perhaps you could slap 16k of RAM in the cartridge. – Dampmaskin Nov 7 '19 at 8:33
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    github.com/apoloval/msx-cartridge ("Schematics and PCB designs of cartridges for MSX systems") doesn't seem to go below 64kb, but is it nevertheless helpful? – Tommy Nov 7 '19 at 18:35
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    @Dampmaskin If I'm understanding correctly the two versions just require different amounts of ROM (16k vs 32k), not RAM. – mnem Nov 7 '19 at 19:27
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    Oh, it's ROM not RAM. Ok, but what I still don't get is the purpose of having two versions of the circuit. Are there MSX machines out there that are unable to run a 32k ROM? Sorry if I'm being dense. – Dampmaskin Nov 8 '19 at 23:24
  • Maybe have a look at github.com/apoloval/msx-cartridge (can't say if it's good though) – JeanPierre Nov 11 '19 at 17:30

16 KB cartridge does not require any additional components, you connect OE to the /CS1, and CE to the /SLTSL signal.

32KB cartridge also does not require any additional components, you connect OE to the /CS12 signal, and CE to /SLTSL signal.

And of course all address and data pins must be connected to the bus.

All above mentioned signals are present on the slot connector.

The design is very simple.


Reading updates to your question I wonder where did you take your assumptions from.

You have EEPROM/flash chip, and you have slot connector, you need to wire them properly so that bus can read contents of the chip (and possibly be able to write to chip if it supports this operation).

  • you connect address lines of the slot connector to the address input of the chip, number of address inputs of the chips defines number of wires from the connector;
  • you connect 8 data lines between bus connector and chip;
  • you connect /SLTSL to the chip's /CE;
  • you connect /CS1 or /CS12 to the chip's /OE;
  • you connect /WR to the chip's /WE (if this chip has this input);
  • you connect pins 45 and 47 together, and connect them to the Vcc pin of the chip;
  • you connect pins 41 and 43 together, and connect them to the GND pin of the chip;
  • you put power decoupling capacitor of 0.1 uf between Vcc ad GND pins of the chip, closer to these pins is the better.

Some ROM/flash chips may have some more inputs (like PGM) and you must read the datasheet and connect them as instructed by the datasheet.

Now to yor question and assumptions.

  • you do not need a pull down resistor on the /OE line unless you are obsessed with electircal termination, but if you are - this possible one-fix-all termination solution is wrong;
  • you should connect /SLTSL to /CE and /CSxx to /OE and not vice versa. You can do other way around, and it will work, but it is practically wrong in terms of power consumption;
  • you must not have +5V and /WR signals of the connector connected together;
  • you can connect +5V to the /WE input of the EEPROM/flash, but then you will not be able to update chip contents in circuit programmatically through the machine;
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  • Though your answer says the design is simple, for being crystal clear, I wanted a circuit diagram in the answer to my question. – Rosemary Nov 15 '19 at 13:37
  • rs.gr8bit.ru/Documentation/YIS805.pdf and rip IC324 connection circuit off it. – Anonymous Nov 15 '19 at 15:06
  • I have given the circuit diagram, in my edited question, based on your answer. Can you check the diagram is correct then I will accept your answer. – Rosemary Nov 18 '19 at 12:28
  • Also the diagram connects SLTSL to OE, but I think it can be connected to OE or CE ; as you state SLTSL connects to CE. – Rosemary Nov 18 '19 at 12:44
  • Using CS1 means the start of the program code is put into the adresses 4000-7FFF (16K of code space between these addresses) in the EEPROM . Using CS12 means the start of the program code is put into the adresses 8000-7FFF (32K of code space between these addresses) in the EEPROM . Right? – Rosemary Nov 18 '19 at 13:24

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)?.

As described in this answer, there is no need for any additional circuitry (*1). This is true for up to 64 KiB (512 KiBit) in size. Only such larger as 64 KiB (often dubbed as Megabit cartridges) do need mapper logic/chips.

These Boards are quite simple:

enter image description here

(Picture taken from a thread on MSX.org about EPROM test boards)

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.

You may use the same board/circuit for both. MSX design was made with lowering cartridge cost in mind - at least for sizes imaginable in the early 80s :) Next to all boards available today (and even several from original games) are configurable.

Since MSX is well supported by new developments, several companies offer simple cartridge boards (and housings) like you need. RC.SE does not favour any such, thus use the engine of your choice and search for 'MSX Cartridge Kit' or 'Empty MSX Cartridge' or 'MSX cartridge PCB'. you'll be surprised about the offers available. Some already include Flash chips like yours.

Now, if you really want to go all the length, several comments on the question have recommended this Githup repository which, on first sight, seams quite adequate. They are made using KiCad. If KiCad isn't your thing, there's a project for a similar PCB up on EasyEDA.

*1 - A buffer capacitor to ease power issues is always welcome.

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  • So to make a cartridge is it as simple as the following? So if I write by game onto an at27c256 chip and solder, with the capacitor, it into the cartridge PCB, given in the photo, in your answer, and IGNORE the modifications explained by the red lines, then will the constructed cartridge work when plugged into an MSX-1 machine? – Rosemary Nov 15 '19 at 1:01
  • @Rosemary Yes, basically it is. Except, it depends on the card you use. So pleast consider its description if one or two bridges need to be soldered as well. – Raffzahn Nov 16 '19 at 23:05

Have you looked at https://hackaday.io/project/8473-msx-protocard? Based on all the information already provided, you may be able to expand the project and do a lot more with it. Check it out! Keep us posted.

Twitter: @msxall

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