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I want to make my own ROM cassette for the Famicom, so I disassembled the cassette.


I want to make my own cassette for the Famicom.


Information collection

To make my own ROM cassette, I need to do the following :.

  1. Obtain a cassette board
  2. Writing programs and data in ROM
  3. Replace the ROM on the cassette board with the ROM on which it was written.

Substrate of the cassette

There are many different types of circuit boards in the cassettes of Famicom. This is because the amount of program and image data that can be accessed by the CPU and PPU of the Nintendo-Famicom is not enough to make the game more interesting and elaborate, and because complex memory access is required.

For this reason, a function has been added to the cassette to convert only necessary areas in the large memory space that cannot be directly accessed by the Nintendo-Famicom.  This special circuit is called a mapper and has more than 100 types.


The top board is the board for "Passion!Professional Baseball".

It is a highly functional cassette with a 1M bit character ROM, a 512k bit program ROM, and an audio playback IC.

This time, I want to make a board called the mapper 0 which is simple and has no special circuit.


There are 3 main types of ROMs that can be written to and erased.

    • UV EPROM
    • EEPROM
    • Flash ROM


It is a very old IC.
About 13V is required to write data.
Also, in order to erase, you need to expose the glass window to ultraviolet rays for about 20 minutes. But it's nice to see the silicon chip (die) from the glass window.
Capacities from 8 KBytes (64 kbit) to 64 KBytes (512 kbit) can be used on the Mapper 0 board.
The 32 KBytes (256 kbit) EPROM model number is 27 C 250 6.

27C256 detasheet

The data sheet also described the writing procedure.


This is an EPROM that can be electrically erased because it is troublesome to erase the EPROM. 

The type that can be used for Famicom is the type that has many pins of the parallel connection, but the current mainstream is the 8 pin type EEPROM of the ISP or the I2C connection, and the parallel type does not seem to be widely distributed.

Flash ROM

This is a rewritable ROM invented by the Japanese, which can read and write faster than EEPROM and is easy to increase the capacity.
Since it is a relatively new IC, the pin pitch is narrow, but if you can convert this pitch, you can use it in the Famicom.

Writing data

Writing data requires a dedicated writer.
EPROM and EEPROM can be written with the above writer.
In the case of flash, the above writer cannot write because the pin is special.
I may be able to write if I convert pins, but I don't know.

Even if you don't have a writer, if you follow the writing procedure of the data sheet, you can write using arduino.


Find the cassette substrate of the mapper 0.

Search titles in Nintendo-Famicom Cart Database

Look for a simple circuit board called Mapper 0 that does not contain any special circuits.
You can find which game title is the number of the mapper on the site called "NES Cart Database".

Search results are here.

110 titles found.

Purchased at a recycling shop

I went to the recycle shop with the list I searched earlier.
I bought  "4 hit mah-jongg"x3 and "baseball"x2.
I bought "mah-jongg" as a bonus.

Now, is there a usable board?

Result of the shell cracking

4 hit mah-jongg

The number on the back of the cassette (does it show the date?
I bought 3 different types.
831018, 851224, 880920.

I opened them.

Only the cassette numbered 831018 was a DIP type board.
Other than that, the IC was directly attached to the substrate and sealed.
The way of making is different depending on the lot.


I bought an old label and a newer one with a picture on it.

I thought the old one was DIP, but the new one was DIP package.
That's surprising.


The mah-jongg I bought as a bonus was a type with IC directly on the board.

Mapper 0 Get 2 Boards

I bought 6 cassettes, and two of them contained DIP type boards.
If I need more in the future, I will buy 831018 "4 hit mah-jongg” or a "baseball”with pictures.

Find the EPROM.

Which EPROM to use

It is nice to see the IC chip, so I think I will adopt UV EPROM, although it is a troublesome IC that requires a high voltage for writing and an ultraviolet lamp for erasing.
Another reason is that it is easy to obtain.

We decided not to use flash ROM because we have to make a conversion board.


I will buy it with my usual Aliexpress.
If you search by 27 c 6, there are many.
It is important to include "NEW" in the search.
If you only search for "27C256", you will find both new and used products.
Some cheap shops sell used ROM.
There are some shops that have a lot of orders, so you should avoid them if there is used information in the feedback. Product - 1 PCS IC M27C256B-10F1 27C256 CDIP-28 NEW GOOD QUALITY

If there is NEW in the title like in the above store, there is a high possibility that you can get a refund by filing a claim even if the used item arrives.
Please refer to this article for information on how to get a refund.
This article happened a long time ago, so it's much easier now.
Also, at the time of order, in the column of "Leave a message for this seller :", "brand new pleae. No USED." (Please give me a genuine new one.
I don't need used ones).
If the shop owner is a good person, he may ask you "Used but OK?" and the possibility of sending a new one may increase.


I was able to get a new UV EPROM without any problems.
I don't know if it's genuine.


I want to make my own ROM writer.
Also, I think I'll make a device to erase ultraviolet rays.
2019.6.4 Postscript : I experimented with lighting an ultraviolet light bulb.