Disclaimer: This tutorial is for educational purposes. The instructions and products discussed are for the creation of homemade games only, or for repairing damaged cartridges for personal use, and should not be used for duplicating and distributing games protected by copyright.

I’ve taken a lot of time to go through and learn all I can about how SNES games work, and I tried my hardest to make a comprehensive and easy-to-follow guide so that you can do it yourself. Luckily, SNES games aren’t actually too complicated to make (way easier than NES games), and there are a ton of different ways you can make them! It is my hope that after reading this tutorial, you’ll have a good understanding on how to make your own SNES cartridges to use in your original SNES hardware. There are some minor soldering skills required, and it might be frustrating at times dealing with older technology, but stick with it and you’ll eventually get the hang of it.

Table of Contents

Step 1: Gather information on your game

Step 2: Determine the method of reproduction

Step 3: Choose your board

– Donor cartridge

– Custom PCB

Step 4: Determine which memory chips to use

Step 5: Fix the checksum and remove the header

Step 6: Finalize files for programming

– 27C801

– 27C160

– 27C322

– 29F033

Step 7: Burn your ROM

– 27C801

– 27C160

– 27C322

– 29F033

Step 8: Double check your chips, and prepare the board

Step 9: Install chips on the board

– 27C801 (donor)

– 27C160 (donor)

– 27C322 (donor)

– 27C322 (donor, ExHiROM)

– 29F033 (donor)

– 29F033 (donor, ExHiROM)

– Custom PCB

Step 10: Finish your game

Equipment you will need

You’ll need a few basic things:

1) Programmer. This is what you use to program the chips the game data is stored on. I got mine on eBay for about $50. It’s a TL866 MiniPro programmer. There’s an updated model, the TL866II Plus, and it seems to work just as well. The TL866 has worked flawlessly for me so far, even after 5 years, and it’s pretty easy to use. There are other more advanced programmers out there, but they run a lot more expensive. If you have one of those other programmers, you’ll have to figure out how to use it yourself (though, if you’re reading this and you already own a programmer, you probably know what you’re doing anyway, nerd).

2) A board. You can use either an existing game that you’ll repurpose, or a custom designed board. Your game will determine which method is easiest, and which you can even use. I provide custom boards of my own design on my store page if you’re interested in supporting the site! I offer board variations for using M27C322 or M27C160 chips or boards that mimic the pinout of the original Mask ROM.

It might sound like pandering, but the prices of SNES games keep going up year after year. A lot of the once bargain-bin games are nearing $10 in some cases. I’d recommend using a custom-made board where possible – even if it’s someone else’s. There are many out there available. Perfectly good SNES games are becoming rarer by the year!

2b) A prototyping board. I have a few boards designated to test ROM files, EPROMs, SRAM, and the CIC chip. Basically, I took one of my custom boards and soldered in sockets to allow swapping of the chips without having solder them in place. When I want to make a game, I program my ROMs, put them in the sockets on the prototype board, then use that in my SNES to check and make sure they work. Once I verify the game is running normally, I know that everything is good to go, and I take them out of the sockets to solder them onto a permanent board. I highly recommend doing this, either with one of my custom boards, or with a donor board you convert yourself. It will save many headaches and prevent having to desolder anything – something I really hate doing. Here’s what one looks like compatible with 27C322 EPROMs:

3) EPROMs or EEPROMS. EPROMs, or Erasable Programmable Read-Only Memory, are older technology (with a single ‘E’) and are erased via UV light. EEPROM on the other hand, has an extra ‘E’ that stands for “Electrically”. The difference between the two is that EEPROMs are erased with electrical signals rather than UV light. Functionally they are nearly identical, and either can be used, though I usually stick to EPROMs because of the price and ease of use. EEPROMs, though, can easily be reprogrammed compared to regular EPROMs. There are definitely benefits to either choice.

In this tutorial, I will go over multiple methods of making games using 8 Mbit, 16 Mbit, and 32 Mbit through-hole EPROMs, and also using 32 Mbit surface mount EEPROMs.

3b) TL866 Programming adapters. If you want to use any of these chips (besides the 40-pin 8 Mbit EPROMs), and you’re using the MiniPro, you’ll need programming adapters so that you can program these chips. They are not natively supported by the TL866, but we can easily add the functionality ourselves. Other programmers like the GQ-4X, can handle all of these chips without adapters, but I’ve never seen that programmer go for less than $100 online. I make these adapters, and can sell them to you over on my store page, or you can make your own, as I provide schematics for them. I’ll go over which one you might need for your project later on.

4) EPROM eraser. This is for erasing your EPROMs. You do not need this if you plan on only using the surface mount EEPROMs. I use this thing a lot for trying out different games on my 27C322 EPROMs that I swap in and out of my prototyping boards so I don’t need to solder the chips in to try a game out. But you should get one regardless if you plan on using prototyping boards or not, because you’ll either need to fix something you programmed at some point, or you’ll have to clear the chips you order since they’ve probably got something written on them.

5) Miscellaneous hardware. You’ll need solder, and a soldering iron, at the very least. You might need some wire if you’re using a donor cartridge, I prefer using 28 gauge. You’ll also need a special screwdriver for opening SNES games, as they use specific screws. You’re gonna want the 3.8mm “Security Bit” screwdriver. The 4.5mm is used for opening Nintendo consoles and Sega games. Might as well buy both though, they usually come in bundles from what I’ve seen online.

So for making games, if you want my personal recommendation, I’d go with using 27C322 or 27C160 EPROMs, with custom PCBs (to avoid destroying the ever-dwindling population of SNES cartridges) or a 27C322 or 27C160 adapter board on a donor cartridge. These larger EPROMs really make it easy to put your ROM on a cart, and using them with adapters or custom boards saves you the headache of adding extra wiring.

Back to top

Step 1: Gather information on your game

If you’re putting your homebrew game on a cartridge, you probably already know all this stuff about your game, but maybe you’ve found an open source game you want to make. The first step you should take is to find out the crucial information of your desired game. To do this, all you need is your ROM file and a few extra pieces of software.

Before we get into the meaty part of the tutorial, we need to apply any necessary patches to your ROM. You most likely won’t have to do this step. If you’re planning on making a translated version of a foreign ROM and the language patch isn’t already applied to the ROM, or you want to add some other patch to a ROM that’s not already part of your file, you’ll have to use a program called Floating IPS to patch it. It’s very simple to use. If you don’t know if you need to use this program, you probably don’t.

Open the program up, and click on “Apply Patch”. The patch you download should have the extension .ips or .bps. Locate and select the patch you want. Then, it will prompt you to apply the patch to the correct ROM. Find the ROM file in your folder and select it. It will prompt you to save it under a new name. That’s it!

Run your ROM in an emulator

It’s important to run your ROM in an emulator to determine it’s the exact game you want to make. Sometimes, a ROM file will be corrupt, or if you had to patch the ROM the patch might be corrupted, or something else could have happened. So you should download an emulator to run the file in. I’d recommend higan for emulation, as it tries to emulate the original SNES hardware as closely as possible, so you’re more likely to catch any errors. Read the User Guide on how to use it – it’s actually a helpful document!

So make sure that the game is the exact version that you want to use, and that it can run for a few minutes without freezing. Nothing worse than finishing a game up and finding out after five minutes at a specific screen there’s a glitch in your homebrew game you missed.

Once you’ve verified that your ROM is correct, you’ll need to download the most important program we will use, called uCon64. This is a command line utility that will give you all the information you ever wanted to know about your ROM. Using it is a bit tricky, though, so I’ll go through exactly what you need to do here.

(I recommend making a folder where you can put all of your work materials to make it easier to navigate.)

Download and unzip uCon64. Now, open Command Prompt. Change the directory to the folder where uCon64 is located by using the cd command (it’s located on my D drive, shown below). If the cd command doesn’t work, try adding /d after it.

cd [path to folder] OR cd /d [path to folder]

Now, navigate to the place where your ROM is located. Hold the shift key and right click on the ROM, and click “Copy as path.” Now, go back to your Command Prompt screen and enter:

ucon64 [path to ROM]

Use CTRL+V to paste the path. Now hit enter, and you’ll get a lot of information in front of you.

Let’s take some time to go over what each of these categories are.

Bank Type

There are two main types of banks known as HiROM and LoROM. In the command window, HiROM games will display as “HiROM: Yes” and LoROM games will display as “HiROM: No”. Pretty self explanatory.

Note that the ExHiROM format will show up as HiROM.

SRAM

Some games use SRAM, some do not. If yours uses SRAM, you should try to provide it with the exact amount it requires. The reason being is that some games check to see if the amount of SRAM available equals a specific amount. Worst case, give it more SRAM than it needs, and if it doesn’t work, you can always make some adjustments to the larger chip to make it look like smaller amounts of SRAM.

Chips

This column lists any specialty chips the game uses. This doesn’t include the chips that are default on all games, like the CIC region chip or the ROM chips. For example, Star Fox 2 uses the Super FX chip.

Another common thing that many games use are batteries. I’d recommend buying a handful of new batteries with battery holders if your game uses one, even if you’re converting an older cartridge to a different game. It’s been about 30 years since many of these games came out – their batteries are probably almost dead, if they aren’t already. I recommend getting the yellow ones that come pre-mounted. The original batteries are spot-welded to the holders so they don’t move – replacing just the batteries without removing the mountings is tricky and not worth the time.

Region

You need to make sure the ROM you’re using is formatted for the correct region – PAL or NTSC – otherwise, they won’t run well (or at all) on your SNES/Super Famicom. Look up where you live and if it’s in the PAL region or the NTSC region if you’re unsure. Converting a game from one region to another is difficult or impossible, and it isn’t as easy as disabling the region lockout chip (CIC chip). Countries in the PAL region run on 50 Hz power, where countries in the NTSC region runs on 60 Hz power, and this causes some games to run faster or skip frames if you use them in the wrong region. Analog video encoding is a tricky thing.

ROM Size

This is how large your game is, obviously. The size only comes into play when you’re deciding which chips to use to program your game, because most cartridge boards are capable of handling pretty much any size game you can make. Remember that if your game is larger than 32 Mbit uCon64 says it’s HiROM, you’ll actually be making an ExHiROM game.

Speed

This corresponds to the data access delay times of the ROM. You can pretty much ignore this, as most EPROMs and EEPROMs available anymore will be fast enough for both types of games. If you’re worried, make sure the datasheet of your chip specifies AT LEAST 120 ns access time (120 ns or less). I’ve never run into one that was slower than this though. If you’re curious about the differences between SlowROM and FastROM, check out my detailed write-up about the SNES cartridge inner workings.

Knowing all this information now, you should note the region, ROM size (specifically the number shown in Mb), SRAM size, bank type, and chips that this screen shows. With this information, we can determine exactly how we want to make this game.

Back to top of Step 1

Step 2: Determine the method of reproduction

There are two ways you can make a reproduction cartridge. You can use a donor cartridge, which refers to taking an older game (hopefully a cheap, very common one) and removing the ROMs and replacing them with your own. The other option is to use a brand new board to make the game. There are pros and cons to each. But before we get into the nitty gritty details, your decision might already be made for you.

Look at the type of chips that uCon64 listed for your game in Step 1. If this says anything EXCEPT a combination of ROM, SRAM, and/or Battery, you must use a donor cartridge. There are a handful of specific games that use special graphics chips. An example of this would be the game Star Fox 2. It uses a SuperFX chip to help with the graphics. Unfortunately, short of using a flash cartridge (which are pricey), there isn’t any easy way to reproduce a game from scratch that uses these specialty chips. Some games do have a few patches out there that let you run the game without the special chips, but this is gonna be a case-by-case thing. So once again, if you’re making a game that uses anything but the normal types of chips seen on a cartridge, you must use a donor cartridge. Skip ahead to Step 3a.

If your game uses normal run-of-the-mill chips, then you’ve got a decision to make! Let’s go over the differences between donor cartridges and custom PCBs.

Using a donor cartridge

Using a donor cartridge involves taking the Mask ROM chips off the existing board and replacing them with EPROMs or EEPROMs that you program yourself.

Pros to using a donor cartridge:

You won’t have to supply your own plastic case. The cartridge comes with the necessary components, like RAM and the CIC lockout chip, and various resistors and capacitors on the board. Because of these, the price can be cheaper than using a custom PCB.

Cons to using a donor cartridge:

You might have to remove or cut pins on the existing ROM (and possibly the battery), which can be a huge pain, and if done without caution, can easily damage the board. The assembly might look messy with a lot of extra wires, depending on the chips you use to program the game on. You’re destroying an otherwise good SNES game. If you’re a proponent of video game preservation (as I am), this probably won’t appeal to you. Though, you’ll probably be destroying a crappy sports game, so use your best judgement. Removing stickers from cartridges is my least favorite part of the entire process. It seriously sucks.

Using a custom PCB

There are a few different sellers out there that will sell you PC boards that you can use in your SNES as cartridges – OR, you could use mine!

Pros to using a custom PCB:

The final build will look a lot cleaner, since you won’t need to rewire anything. You don’t have to spend time figuring out a compatible game to use as a donor cartridge. You can easily turn one into a prototyping board with sockets for all the chips so you can test games out before you solder them directly to the board. You’ll be supporting the SNES reproduction community! And you won’t be destroying a perfectly good soon-to-be-endangered SNES cartridge in the process!

Cons to using a custom PCB:

You need to buy the board, extra components (such as SRAM, capacitors, and a lockout chip), and the plastic case, possibly making the final cost more expensive. However, I do offer a version of my 27C322 board with many of the parts populated already for you, so you don’t have to worry about any of that. Like I said before, you will only be able to make games that do not use specialty chips.

Now that you have a better idea of how you want to make your game, let’s get the proper board. Skip ahead if you’re using a custom-made board.

Back to top of Step 2

Step 3a: Choose your board (donor cartridge)

First, you’ll need to open up this Excel document I made. This document has information on most available ROMs for the SNES/Super Famicom, including all foreign games, and even some ROM hacks. I got the information for this spreadsheet from the SNES ROM Header Database. I trimmed some of the fat off of the list, like games that have weird amounts of SRAM or customized things that didn’t filter well in the Excel document.

Go back to your notes on the bank type, SRAM amount, and extra chips that your game uses. You should filter the columns for those characteristics to find a good, cheap donor. Note that instead of filtering the region column, you should filter the video column instead depending on if you’re in the NTSC or the PAL region.

To find a donor cartridge, go to each of the filtered column drop down menus. Deselect each value that your game DOESN’T have in the Bank, SRAM, Chips, and Video columns. I also sorted the list by the game column from A to Z to group all common games together – makes it easier to sort through the titles. You should now have a list of compatible games. This screenshot shows all the HiROM games with 64 Kbit of SRAM in the NTSC region.

Note that you should be sure that the game you pick for a donor isn’t a hack or mod itself, because that won’t be the actual cartridge you can buy! Make sure the game you pick has an entry in the sheet that either has [!] or no additional information past a version number and region code (NOT translation code). There are a few games that, from what I’ve seen, will use HiROM instead of LoROM if you have a certain translation or mod. You will be buying an original game so you MUST make sure the original is on your donor list!

Looking through the list for this hypothetical game, you should see these: Earthbound, Final Fantasy III, Illusion of Gaia, Madden NFL ’95 through ’98, NBA Hang Time, NHL ’95 through ’97, Secret of Evermore, etc. So, theoretically, you could take an Earthbound cartridge and use it to make your game. I don’t recommend this, obviously, but it’s possible! How about we use something cheap that’s in retro video game bargain bins across the world, like Madden NFL ’95? Basically, any games that have the same characteristics in these important fields are interchangeable and can be used to make other games with the same characteristics. The good news is from what I’ve found, there are usually a wide variety of cheap games you can use to make most other games.

Now, if you want, you can check out your donor cartridge over on SNES Central. Note that the original ROM socket can come in a 32-pin or a 36-pin variety. Some games will have 36-pin sockets, but only use 32-pin ROMs. You’ll have a MUCH easier time with the reproduction if you get a board that has a 36-pin socket, so if you can, I recommend trying to pick a game that uses that kind of board. Also, some games come with two or three ROM chips on them – I won’t be covering those types of boards in this tutorial, as they’re going to change on a case-by-case basis. Perhaps in the future I’ll put up guides for specific multi-ROM boards.

Another important note is that some games that use specialty chips will use surface mount parts on their boards instead of through-hole parts. This makes using them for reproductions a lot trickier. It’s still possible, but they’re not the easiest to work with. I will not be covering those types of games in this tutorial.

Once you have your donor cartridge, you should DEFINITELY check to see if it works as is in your SNES. You don’t want to get to the end of the process only to find the game you bought is broken (which has happened to me). You might have to clean the cartridge edge to get it to work. Now, let’s decide the next most important aspect of your repro – what chips to load your ROM on. Head to Step 4.

Back to top of Step 3a

Step 3b: Choose your board (custom PCB)

I currently offer two boards – one that matches the original Mask ROM pinout on the SNES cartridges, and one that accommodates up to two 27C322 or 27C160 EPROMs. The SNES ROM duplicate board supports games up to 32 Mbit, and the 27C322/160 board supports up to 64 Mbit games. They both support up to 256 Kbit SRAM as well.

If you elect to use someone else’s board, that’s fine, you’ll just have to rely on them for instructions where it isn’t clear what to do. Note that if your game doesn’t save, you’ll only need a few capacitors, the CIC chip, and the ROM chip. If your game does save, you’ll need basically every component. We’ll get into that later on.

Now let’s decide the next most important aspect of your repro – what chips to load your ROM on. This will determine exactly which of my boards you’ll be using, so if you’re not sure which to use just yet, read on and figure out what works best for you!

Back to top of Step 3b

Step 4: Determine which memory chips to use

There are four widely used memory chips to load your ROM into that I will go over in this section. Which you choose will be determined by a few factors, most notably your ROM size, and if using a custom PCB, the compatibility of your board.

27C801 – a through-hole 8 Mbit EPROM

– a through-hole 8 Mbit EPROM 27C160 – a through-hole 16 Mbit EPROM

– a through-hole 16 Mbit EPROM 27C322 – a through-hole 32 Mbit EPROM

– a through-hole 32 Mbit EPROM 29F033 – a surface mount 32 Mbit EEPROM

There are plenty of alternatives with the same pinouts that will work just as well as these four (such as the M27C080 for the 27C801, or the 29F032 for the 29F033). I’ll be using these numbers listed above when referencing these chips to make the tutorial easier to read.

There are a ton of different ways to make games with these chips. I’m only going to cover the most common and easiest to use cases here. For that reason I recommend you getting a chip that’s either as big or bigger than the ROM you want to put on a cartridge. The exception being ExHiROM games, larger than 32 Mbits. For those games, you can use two 27C322’s or two 29F033’s, and do some extra wiring that I’ll go over later.

As far as my personal preference goes, I’ve been using 27C322’s for most of my games for a while now. I stay away from 29F033s because of the relative difficulty in soldering them, but if you can get them mounted properly they are quite handy.

Checking your ROM in the SNES ROM Utility

Before you continue, you should download the SNES ROM Utility program and load up your ROM. We’re going to be using this program pretty heavily. Most games should load up fine, but you might get some errors. In the cases where your ROM doesn’t load, you’ll have to do some research or possibly use another version of your ROM.

8 Mbit EPROMs

If your game is only 8 Mbit large, you can very easily and cleanly use just one of these EPROMs, like the 27C801. There are only two pins you’ll need to reroute. These are getting a bit expensive from what I’ve seen, but they make for very clean installs of smaller games. Check it out:

16 Mbit EPROMs

16 Mbit EPROMs, like the 27C160, I’ve found to run cheaper than the 801’s. There are only two downsides to using these chips. For one, it’s going to look ugly, as it requires a bunch of wires similar to the picture above – unless you use an adapter board like this one, or this other version that’s extended above the donor PCB and requires no desoldering. Secondly, you’ll need a special programming adapter to program these in the MiniPro programmer.

Here’s what your game is going to look like with just one 27C160 (without an adapter board).

And here’s what a cleaner install looks like with the adapter board I mentioned.

32 Mbit EPROMs

32 Mbit EPROMs are the largest through-hole parallel data EPROMs available. Luckily, most SNES games are 32 Mbit or smaller. I use the 27C322. Like the 27C160’s, they will look ugly if you’re using a donor board without an adapter – it has 42 pins, so you have to wire each pin individually to the socket correctly. In addition, you’ll need to provide two multiplexer ICs to change the 16-bit data bus of the 27C322 into an 8-bit data bus of the standard SNES cartridge. Also like the 27C160’s, you’ll need a programming adapter to program them on the MiniPro which I can provide you with.

Like the 27C160s, in order to remove all the manual wiring, I do sell these adapter boards that do the wiring for you! They’re extremely handy, and I don’t think I’d recommend using these chips on a donor cartridge without them. I also provide an extended one that’s a bit easier to use and doesn’t require any desoldering.

I have never created a game with 27C322’s without an adapter board like this, because having those multiplexers just hanging in the cartridge without being secured to anything is not something I want to deal with. Also, the final product looks so nice and clean!

Here’s what it looks like with the slim adapter (note that my boards are green, not red).

And here’s what it looks like with the extended adapter. Note that with the extended boards, you don’t have to desolder the original ROM!

Personally, I prefer the way my custom boards look with 27C322’s in them, but I’ll admit, I’m a bit biased.

32 Mbit EEPROMs

As for the 32 Mbit EEPROMs (I used 29F033 chips), I got these from eBay for about $8 each. I haven’t checked prices recently though. These are surface mount parts, so an extra breakout board is necessary to program and insert into the SNES PCB. You can get these boards from various places, like buyicnow. Sometimes they come pre-mounted and tested, so that’s pretty nice.

The upside to using the 29F033 is that everything will look a lot cleaner and the process will be much quicker (once it’s mounted to a board), as you won’t need to do any rewiring. The downside besides the price is, well, it’s a lot harder to solder surface mount parts than it is through hole. If you don’t have any experience soldering surface mount, and you buy them separate from the board, this might be a harder option for you.

The type of pins you’re gonna be soldering are circled in red in that picture above. So my advice, only if you are confident in your ability to solder extremely small pins and are willing to spend a bit of extra money to make your life marginally easier, is to use the surface mount 32 Mbit EEPROMs with breakout board only for any game larger than 16 Mbits. But again – this is a difficult process, especially if you’re new to soldering. And you might kill a few of these chips if you don’t solder them properly by keeping heat on the pins for too long. If you haven’t had a lot of experience in soldering such tiny pins, or aren’t willing to potentially waste a bit of money in damaged chips, I would recommend just using the through-hole EPROMs.

But if you feel so bold, my tips if you’re wanting to try to solder this surface mount chip: get yourself a flux pen. Flux will make your solder flow much better, and is essential if you want to attempt this (trust me… I tried to do it without it). Just spread it on all the pins. And maybe invest in an adjustable magnifying glass stand. Make sure you have really good lighting. And lay off the coffee… you need steady hands for this one. Here’s what a final board looks like with one of these EEPROMs. Very clean!

Note that if you plan on going this route, and you want to use the TL866 programmer, you’ll need to either buy my adapter, or make your own to route the wires on the breakout board to the programmer. Also note, custom SNES PCBs that have the original SNES Mask ROM socket (like mine) can accommodate these chips on adapter boards.

Figured out which chips and what kind of board you want to use? Great! Let’s get your ROM file ready to program.

Back to top of Step 4

Step 5: Fix the checksum and remove the header

Now you’ve chosen what kind of board you’re going to use and your chips, let’s take a look at that command window again.

Let’s start with the checksum. If the checksum areas say “OK” and are green, you’re good to go! Skip over this section.

Fixing the checksum – IpsAndSum

In the picture above, my checksums are bad (this usually only happens when games are translated or modded). If your checksums are bad, then you need to run your game through a program called IpsAndSum. This program is a bit glitchy, but it’s pretty easy to figure out.

First, you’ll need to go to File > Open, and choose your ROM. Sometimes the numbers will change in the fields on the screen, sometimes they’ll stay at 0000. Like I said, glitchy. Either way, go back to File > Repair SNES CheckSum, and the fields should change. Click “Yes” to repair. Then, make sure you go to File > Save to save your fixed ROM.

You should run the ROM through uCon64 once again to make sure the checksums got fixed, and that you remembered to hit File > Save (this happens more often than you’d think).

At this point, if your checksums are still bad, you might have to try another ROM if possible, or try going through the steps again in case you missed something along the way. I’ve read that it might still work if you go ahead without good checksums, but I’ve never tried it as I haven’t run into that problem as of yet, so proceed at your own risk. Maybe you can try it out on a prototyping board like I mentioned earlier to avoid having to solder anything down onto the board.

Removing the header – SNES ROM Utility

Here’s what the screen looks like when you load a ROM into it.

You’ll see some of the information of the ROM here that you already saw in uCon64.

We’ve got a crossroads here. The process for preparing the different memory chips is varied. So, click on the link of the chips you’ll be using.

Step 6a: Finalize files for programming (27C801)

Step 6b: Finalize files for programming (27C160)

Step 6c: Finalize files for programming (27C322)

Step 6d: Finalize files for programming (29F033)

Back to top of Step 5

Step 6a: Finalize files for programming (27C801)

If you’re using the 8 Mbit EPROMs, there’s really only one option we’ll need to pick under the task list – SwapBin. This command does everything – it removes the header for us and performs a process that switches the data in the ROM around to make our modifications to the cartridge a bit easier.

Check the SwapBin button, choose 27C801 on the drop down menu and click OK. You’ll get this notification, and if you look in the folder where your ROM was located, you should see a new file created.

Note that if you load up a game larger than 8 Mbits, it’ll split the ROM into multiple files. You can do this like I mentioned, but you’ll need to wire up some extra hardware and chips, which I go over in the old tutorial if you’re interested. But really, it’s such a hassle, I don’t recommend doing it.

Explanation of SwapBin

This is really only if you’re curious why we do this step. If you’re not, carry on to Step 7a.

Compare the pinouts between the SNES ROM socket and the 27C801 EPROM we are going to use. Like the NES, the SNES games use a proprietary pinout for the ROMs, so we need to do some rewiring.

However, many of these pins line up to other data pins. For example, pin 1 on the 27C801 is A19, but on the SNES PCB, this pin is A17. So, instead of having to rewire A17 and A19 to different places, we can use software to digitally swap these two address pins by modifying the hex code. That way, we effectively change the pinout of the 27C801.

SNES ROM Utility switches A19 with A17 and A16 with A18. Now there’s only two extra wires we’ll have to solder for this EPROM to swap /OE and A16 (since /OE can’t be changed).

Now that you know why we’re doing this SwapBin business, skip ahead to Step 7a.

Back to top of Step 6a

Step 6b: Finalize files for programming (27C160)

If you have a programmer that can natively program a 42-pin EPROM, then all you have to do is remove the header. Easy! Then, skip ahead to Step 7b. If you have a TL866, you’ll need the 27C322/160 programming adapter.

So what the adapter board does is trick the TL866 into thinking we’re programming a different EPROM. The EPROM we’re going to tell it to program is only 4 Mbits large. Using this EPROM normally would only utilize address pins A0 through A17. The 27C160 goes up to A19. By manually controlling A18 and A19, we can program our ROM in 4 Mbit chunks.

All you need to do is load your ROM into the utility, and check the “Split File” button. Then, on the drop down menu, pick 512kB (512 kilobytes = 4 megabits). Luckily, if the ROM has a header, the Split File option will automatically remove it for us when it splits!

Since this ROM is 16 Mbit, it will split into 4 separate files. Your folder should now contain multiple files that are 512 KB large. Now, skip ahead to Step 7b where we’ll program these chunks individually into our EPROM.

Back to top of Step 6b

Step 6c: Finalize files for programming (27C322)

If you have a programmer that can natively program a 42-pin EPROM, and your game is 32 Mbit or less, then all you have to do is remove the header. Easy! Then, skip ahead to Step 7c.

If you’re making an ExHiROM game, and your programmer can program a 27C322 without the adapter, you’ll need to do a bit of extra work, so skip ahead to this section.

If you have a TL866, you’ll need the 27C322/160 programming adapter. Note that for the TL866, you can do the following steps even for ExHiROM games.

So what the adapter board does is trick the TL866 into thinking we’re programming a different EPROM. The EPROM we’re going to tell it to program is only 4 Mbits large. Using this EPROM normally would only utilize address pins A0 through A17. The 27C322 goes up to A20. By manually controlling A18, A19, and A20, we can program our ROM in 4 Mbit chunks.

All you need to do is load your ROM into the utility, and check the “Split File” button. Then, on the drop down menu, pick “512 kB”(512 kilobytes = 4 megabits). Luckily, if the ROM has a header, the Split File option will automatically remove it for us when it splits!

Since this ROM is 32 Mbit, it will split into 8 separate files. Your folder should now contain multiple files that are 512 KB large. Now, skip ahead to Step 7c to learn how to program these chunks individually into our EPROM.

Using multiple 27C322s for ExHiROM

If you’re using my programming adapter for the TL866, and you followed the instructions above, you should have split your ROM file already into 4 Mbit chunks. That’s all you’ll need, so go ahead and move on to Step 7c. If your programmer can handle the 27C322 without the programming adapter, then you’ll have to do a bit more work.

First, check the “Split File” option. Now, choose the “2048kB” option (2 Mbyte, or 16 Mbits) and click OK. In this example, the ROM is 6 Mbyte large (48 Mbits), so this will split it into 3 files, each 2 MByte large (16 Mbits).

Now you should have 3 files in your folder that are 2 Mbyte large. That means we’ll have to stitch the first two together to get a full 4 Mbyte, or 32 Mbit, file for the first EPROM, and put the last 16 Mbit file on the second EPROM.

We need to stitch together the two files that end in 01 and 02 to make the file for the first EPROM. We can do this easily in the command prompt, but first we should rename the files to something short to make it easier for us to type – let’s do ROM_01 and ROM_02. Maybe name it something relating to your game.

Now, open a new command prompt window, and mount it to the folder your pieces of the ROM are in. Type in this command:

copy /B "ROM_01.sfc" + "ROM_02.sfc" ROM_A.sfc

This will create a new file, ROM_A.sfc, that will be a combination of both the files stitched together. MAKE SURE you have the order correct! This is what the command prompt should look like:

Now, you should go ahead and rename the third file (the one that ends in _03) to ROM_B, for consistency. You should now have two files – ROM_A, which is 4 MByte (32 Mbit) large and will go on the first EPROM, and ROM_B, which is 2 Mbyte (16 Mbit) large and will go on the second EPROM. Note that the second EPROM won’t be filled completely – this is OK. I’ve tested it and it still works with the second half of the chip empty.

If you have a ROM hack or other game that is larger than 48 Mbit, you’ll still need two 32 Mbit EPROMs, but you’ll have to stitch the 03 and 04 files into one file using the same method. Now, skip ahead to Step 7c to find out how to program your EPROMs.

Back to top of Step 6c

Step 6d: Finalize files for programming (29F033)

This step is super easy if you’re only using one 29F033 EEPROM. If when you load your game into the Utility, and it shows that it has a header, just check the “Remove Header” option and click OK. If you don’t have a header, and your game is 32 Mbit or less, then you’re already done! Go to Step 7d.

Using multiple 29F033s for ExHiROM

If you’re using multiple 32 Mbit EEPROMs because your game is larger than 32 Mbit, check the “Split File” option. Now, choose the “2048kB” option (2 Mbyte, or 16 Mbits) and click OK. The example ROM below is 6 Mbyte large (48 Mbits), so this will split it into 3 files, each 2 MByte large (16 Mbits).

Now you should have 3 files in your folder that are 2 Mbyte large. That means we’ll have to stitch the first two together to get a full 4 Mbyte, or 32 Mbit, file for the first TSOP EEPROM, and put the last 16 Mbit file on the second TSOP EEPROM.

We need to stitch together the two files that end in 01 and 02 to make the file for the first EEPROM. We can do this easily in the command prompt, but first we should rename the files to something short to make it easier for us to type – let’s do ROM_01 and ROM_02.

Now, open a new command prompt window, and mount it to the folder your pieces of the ROM are in. Type in this command:

copy /B "ROM_01.sfc" + "ROM_02.sfc" ROM_A.sfc

This will create a new file, ROM_A.sfc, that will be a combination of both the files stitched together. MAKE SURE you have the order correct! This is what the command prompt should look like:

Now, you should go ahead and rename the third file (the one that ends in _03) to ROM_B, for consistency. You should now have two files – ROM_A, which is 4 MByte (32 Mbit) large and will go on the first EEPROM, and ROM_B, which is 2 Mbyte (16 Mbit) large and will go on the second EEPROM. Note that the second EEPROM won’t be filled completely – this is OK. I’ve tested it and it still works with the second half of the chip empty.

If you have a ROM hack or other game that’s larger than 48 Mbit, you’ll still need two 32 Mbit EEPROMs, but you’ll have to stitch the 03 and 04 files into one file using the same method. Now, skip ahead to Step 7d to find out how to program your EEPROMs.

Back to top of Step 6d

Step 7a: Burn your ROM (27C801)

As usual, make sure you blank check your EPROMs before you program them and clear them if necessary. I think you’re smart enough to figure out how to program your EPROMs with your programmer, especially if its the TL866 – it’s super easy to figure out. I believe in you! You’ll also want to tape over the little window so the games don’t get randomly corrupted sitting out on your desk.

Now go ahead and skip ahead to Step 8, where we’ll get our board ready.

Back to top of Step 7a

Step 7b: Burn your ROM (27C160)

These instructions are for the TL866. If you’ve got a different programmer, go ahead and burn your ROM, then skip to Step 8.

Burning your 16 Mbit EPROM, as I mentioned before, requires you to trick the programmer. What we’re going to do is program the 4 Mbit chunks we just made, and manually change the A18 and A19 pins. You can do this yourself by making your own adapter, or you can buy mine.

The 27C160 is programmed through the data pins Q0 – Q15. This is a bit different than the 8 Mbit EPROMs and the 32 Mbit EEPROMs, which only use 8 data pins (Q0 – Q7). In its default state, the 160 is a 16-bit EPROM, though, we can make it output in 8-bit mode, which will be covered later. For now, we just need to know that we need to program our ROMs using all 16 bits.

As I said earlier, the TL866 doesn’t support the 160. However, it does support other, smaller 16-bit EPROMs, like the 27C4096. The 4096 is a 16-bit EPROM, however, it can only store 4 Mbit of data. That’s why we split the ROM into 4 Mbit chunks. We’re going to trick the TL866 into thinking we’re programming the 27C4096, when in reality, we’re going to be programming our 27C160 and manually switching the top two bits, A18 and A19, between 0 and 1. This will give us 4 sections of 4 Mbit chunks, for a total of 16 Mbits. A18 and A19 represent what’s known as “banks” of data.

Using the ready made adapter

Here’s what my adapter board looks like:

As you can use this adapter for the 27C322’s as well, make sure the switch is in the 27C160 position.

If you’re instead interested in making your own adapter, I provide the schematic and details of operation over on my documentation page.

Programming the 27C160

So now, you can get to programming. Load up the 27C4096 chip on the TL866 software, and load up the first file from your ROM (ending in _01). Change the VPP to 12.5 V, as this is dictated for programming voltage in the datasheet for the 160. Then, uncheck the “Check ID” option. Your window should look like this:

Here’s a table of how data is programmed into the EPROM. If A18 or A19 is a “0”, that means tie it to GND, or if you’re using the adapter, put the switch in the “OFF” position. If it’s a “1”, that means tie it to VCC, or if you’re using the adapter, put the switch in the “ON” position. Program the 4 Mbit chunks that were made by SNES ROM Utility in sequential order in the banks.

If you get an error while programming with the MiniPro – make sure your chips are in the correct orientation, each bank is blank, and that you’ve selected a 27C4096 EPROM from the Select IC list! Also, make sure you’ve got the switch on the adapter board on the 160 option (if you’re using the combination adapter board). Now, carry on to Step 8.

Back to top of Step 7b

Step 7c: Burn your ROM (27C322)

These instructions are for the TL866. If you’ve got a different programmer, go ahead and burn your ROM, then skip to Step 8. Be sure if it’s an ExHiROM game to mark the two halves correctly so you don’t mix them up.

Burning your 32 Mbit EPROMs, as I mentioned before, requires you to trick the programmer. What we’re going to do is program the 4 Mbit chunks we just made, and manually change the A18, A19, and A20 pins. You can do this yourself by making your own adapter, or you can buy mine.

The 27C322 is programmed through the data pins Q0 – Q15. This is a bit different than the 8 Mbit EPROMs and the 32 Mbit EEPROMs, which only use 8 data pins (Q0 – Q7). We’ll have to add a bit of extra circuitry to use them in the SNES cartridge, but for now, we just need to know that we need to program our ROMs using all 16 bits.

As I said earlier, the TL866 doesn’t support the 322. However, it does support other, smaller 16-bit EPROMs, like the 27C4096. The 4096 is a 16-bit EPROM, however, it can only store 4 Mbit of data. That’s why we split the ROM into 4 Mbit chunks earlier. So we’re going to trick the TL866 into thinking we’re programming the 27C4096, when in reality, we’re going to be programming our 27C322 and manually switching the top three bits – A18, A19 and A20 – between 0 and 1. This will give us 8 sections of 4 Mbit chunks, for a total of 32 Mbits. A18, A19, and A20 represent what’s known as “banks” of data.

Using the ready made adapter

Here’s what my adapter board looks like:

As you can use this adapter for the 27C160’s as well, make sure the switch is in the 27C322 position (shown above).

If you’re instead interested in making your own adapter, I provide the schematic and details of operation over on my documentation page.

Programming the 27C322

So now, you can get to programming. Load up the 27C4096 chip on the TL866 software, and load up the first file from your ROM (ending in _01). Change the VPP to 12.5 V, as this is dictated for programming voltage in the datasheet for the 322. Then, uncheck the “Check ID” option. Your window should look like this:

Here’s a table of how data is programmed into the EPROM. If A18, A19, or A20 is a “0”, that means tie it to GND, or if you’re using the adapter, put the switch in the “OFF” position. If it’s a “1”, that means tie it to VCC, or if you’re using the adapter, put the switch in the “ON” position. Program the 4 Mbit chunks that were made by SNES ROM Utility in sequential order in the banks.

If you get an error while programming with the MiniPro – make sure your chips are in the correct orientation, each bank is blank, and that you’ve selected a 27C4096 EPROM from the Select IC list! Also, make sure you’ve got the switch on the adapter board on the 322 option.

If you’re making an ExHiROM game, then do this process again for your second 27C322 and your second set of ROM chunks. Make sure to mark your EPROMs so you know which is the first half and which is the second half.

After you program your eight chunks, carry on to Step 8.

Back to top of Step 7c

Step 7d: Burn your ROM (29F033)

If you’re using the surface mount EEPROM with the adapter board I mentioned earlier, you’ll need to do a bit of extra wiring to accommodate for the breakout board. Nothing extreme! The good news is your board will look much cleaner in the end compared to the boards you make using the DIP package EPROMs from above.

Preparing the DIP36-TSOP40 Board

On the DIP36-TSOP40 adapter board, you might have noticed a few extra pads on the top of the board. (The board I’m using for this example is from buyicnow.com, it’s version III. Other versions should work fine, but you’ll need to check for differences).

The pads we are going to worry about (R1 and R3) connect to the RESET and the /WE pins. These pins aren’t directly routed to any of the pins for the DIP package, as the SNES ROMs don’t use these pins. But, in order to program our 29F033, we need to do something about these pins. R1 connects the RESET pin to Vcc. This will ensure the chip is always on, which is obviously what we want. R3 connects the /WE (write enable) pin to pin 36 on the DIP package. This will be used by our programmer to enable writing the code to the chip, but when the adapter board is connected to the SNES PCB, this pin will be pulled to Vcc during operation, ensuring the chip never re-enters Write mode.

We need to short both R1 and R3. The easiest way to short these pads is to strip back a wire that covers both pins, solder both pads onto the wire, and then clip the remaining piece of wire. If you want, you could also spread some flux on the pads and short them that way, but be careful not to heat up the pads too much, because you don’t want them to fall off (which is something I’ve done…)

You can completely ignore SJ1 and R2. Not necessary for our project.

Using the ready made adapter

Normally, to program surface mount chips, you usually need to get some sort of adapter for your programmer. They look like this:

All you do is drop your surface mount chip in the little box and make sure the pins are lined up, and you can program it like a normal through-hole chip. Now, these things are stupid simple. They’re literally just traces that reroute the tiny little pins on the surface mount package to larger, DIP-sized pins that your programmer accepts. I get that it’s a niche product, but still. I don’t want to drop extra cash on one of these things. If you think you’ll be programming a ton of these little guys, you can go ahead and pick one up, but I don’t use EEPROMs all that much outside of these reproductions.

With our DIP36-TSOP40 adapter board, we kind of have an adapter already. It’s just attached to a single chip. The problem is, this adapter board we have adapts the pinout to the SNES Mask ROM pinout, which is (unsurprisingly) NOT the same pinout that our programmer uses. So we have to make an adapter for our adapter.

That was hard to type. Anyway, here’s what my adapter adapter looks like.

If you want to learn how to make your own instead, head over to my documentation page. Once you have your adapter ready, place your chips in and blank check, clear if you need to, and program your game.

If your game is going on two separate EEPROMs because it’s larger than 32 Mbit, make sure you label the EEPROMs accordingly.

Back to top of Step 7d

Step 8: Double check your chips, and prepare the board

You should definitely check off all these boxes before you go any further. Once you’ve soldered your chips in, getting them out is a risky and very frustrating process! I’ve killed at least a few boards because I ripped the pads off from desoldering and soldering so much. Maybe you should make a prototype board to try them out before soldering? Anyway, ask yourself the following:

If using a donor board, is it compatible with my desired game (bank type, region, etc)?

Did the ROM run on an emulator correctly?

Did I remove the header from the ROM file?

Are there any broken traces on the board, specifically beneath where I will be placing the chips?

Is there any extra solder anywhere on the board that might be making unwanted connections?

Did I run ucon64 a final time to absolutely make sure the checksums are correct?

If I split the ROM into multiple chunks for multiple chips, did I label them correctly?

If I split the ROM into multiple chunks for the 160 or 322, did I program the banks in the correct order?

Making sure you’ve done these things will save you a lot of time and a lot of headaches, so make absolutely sure you’ve followed them.

Now, if you’re using a custom PCB, you can skip ahead all the way to Step 9g. As for you donor people, have you gotten all your materials from eBay in the time it took you to read through this wall of text yet?

SNES games can have a lot of different chips, but you’ll only need to worry about one at this point – the original ROM chips. You’ll want to keep all the other chips exactly where they are. Some games have two or three ROMs, but this is uncommon – I won’t be covering those cases in this tutorial, because if I did, this tutorial would be at least twice as long! The ROMs are denoted on the PCB in some way, it’ll say “MASK ROM” or some variant of it. If your game doesn’t have any RAM or specialty chips, the ROMs will be the only large chips on your board.

You can see above that U1 is labelled as MASK ROM, which is the chip we need to remove. U2 is the SRAM, which we want to keep in the board.

Note that if you’re using one of my extended adapter boards, you don’t need to remove the original ROM! Very handy! Go ahead and skip ahead a few paragraphs.

Removing the Mask ROM from their boards is kind of difficult, but you have a few options. The easiest way to remove these is to use a desoldering gun, that is, a soldering iron connected to a vacuum. These are pretty pricey, so I don’t necessarily recommend getting one for this. I use a vacuum pump desolder tool. I bought this model, and it works well enough.

Another easy option is to just take a Dremel and physically cut all the pins on the chip, then heat up each individual pin left in the hole with a soldering iron and use pliers to pull them all out. It’s not like you’re gonna need the original ROM when you’re done. Yet another option is to use copper wick to pull the solder off the pins. If you’re going to go this route, you should use some flux as well, to help the solder come off of the pins.

Whatever method you decide to do, make sure not to cut any other traces while you’re doing it! You’ll also want to get rid of all the extra solder left in the holes.

Now it’s time to put your chips onto your board.

Step 9a: Install a 27C801 EPROM on the donor board

Step 9b: Install a 27C160 EPROM on the donor board

Step 9c: Install a 27C322 EPROM on the donor board

Step 9d: Install multiple 27C322 EPROMs on the donor board (ExHiROM games)

Step 9e: Install a 29F033 EEPROM on the donor board

Step 9f: Install multiple 29F033 EEPROMs on the donor board (ExHiROM games)

Step 9g: Populate your custom PCB

Back to top of Step 8

Step 9a: Install 27C801 EPROMs on the donor board

It’s very important to note that usually, the Mask ROM socket on the original SNES PCBs have 36 holes. Like the NES, Nintendo made these boards usable for many different sized games. A 32-pin Mask ROM on a standard SNES game holds games up to 8 Mbit, and a 36-pin Mask ROM could (theoretically) hold up to a 64 Mbit game. Our 27C801 chips only have 32 pins, so we won’t be using the extra 4 holes . You should see a little marking on the board denoting which extra holes are used for the 36-pin chips, and which are used for the 32-pin chips.

Make sure when you put your EPROM in a 36-pin board that pin 1 of your EPROM lines up with pin 1 of the 32-pin socket (or pin 3 of the 36-pin socket).

Now, bend up pins 24 and 31 on your EPROM. Bend the pins SLOWLY and carefully using pliers to make sure they do not snap. Also, solder wires onto the socket holes 24 and 31. These don’t have to be super long, but you’ll have an easier time if you have ample room. Also, try to use thinner wires if you can. This will prevent putting too much stress on your EPROM pins so they won’t snap off.

Now, place your EPROM with bent pins into the socket. Solder the wire from hole 24 to EPROM pin 31, and solder the wire from hole 31 to EPROM pin 24.

Note that keeping the wires shorter (and using thinner wires) helps to make your game easier to fit back into the SNES cartridge. Skip ahead to Step 10 to test your game out.

Back to top of Step 9a

Step 9b: Install 27C160 EPROMs on the donor board

If you’re using one of the 27C160 adapters that I offer (either the compact or extended version), read the article linked there to see how to attach it to your board – luckily, it’s pretty easy to do. Then, skip ahead to Step 10. But if you want to wire the chip up yourself, read on.

The 27C160 is a 16 Mbit EPROM, but that data output can be organized as 8 bits long, or 16 bits long. If the chip is in 8-bit mode, you can store up to 2 Mbit address locations on the A pins. If it’s in 16-bit mode, you can store up to 1 Mbit address locations on the A pins. Since the SNES reads data in an 8-bit bus, we need to put the EPROM into 8-bit mode. This is done by setting the /BYTE pin to LOW logic, or connected to GND. Doing this causes pin 31, labelled as Q15A-1, to act as the new A0, and offset all the address pins by 1 location. So, essentially, A19 will become A20, A18 will become A19, and so on.

Wiring only one of these babies without an adapter board isn’t hard, just a bit tedious. Just follow this handy table down below. You need to wire the pins from the 27C160 to the corresponding socket number on the SNES cartridge. So, for example, pin 1 on the 27C160 goes to hole 32 on the SNES board.

If your cartridge only has a 32-pin slot, then still follow the table above, but you’ll have to find an alternate location to connect pin 42 from the 27C160 to. Follow A20 from the cartridge connector to somewhere you can solder onto. LoROM boards have A20 on pin 46 of the cartridge connector. HiROM boards have A20 on pin 45.

So, find those pins, and follow the traces to an exposed solderable point on the board, and use that as your connection. When you’re done, it’ll look something like this mess.

Pro tip: don’t be like me, use small gauge wire! It’ll make it look nicer, fit in the cartridge easier, and also put less stress on the pins. I just got too impatient to wait for my smaller gauge wire to come in the mail. Now, skip ahead to Step 10 to see if your hard work has paid off!

Back to top of Step 9b

Step 9c: Install one 27C322 EPROM on the donor board

If you’re using one of the 27C322 adapters that I offer (either the compact or extended version), read the article linked there to see how to use it in your board. Then, skip ahead to Step 10. But if you want to wire the chip up yourself, read on.

If you look at the pinout of the 27C322, you’ll notice the data pins go from Q0 to Q15. As I mentioned earlier, that’s because this is a 16-bit EPROM, where each word is 16 bits instead of the 8 bits the SNES uses. When we programmed our 322 using our ROM that was meant for reading in 8 bits, we smashed two 8-bit words into one 16-bit word. So the first address of the 322 contains the first TWO addresses the SNES will use.

Compare the left window here, which is an 8-bit EPROM, with the 16-bit EPROM on the right. Again, these numbers are in hexadecimal, or four binary bits. So you’ll see on the 8-bit bus two-digit hex numbers, while on the 16-bit bus you’ll see four-digit hex numbers.

Let’s use the first two addresses, which are 0x78 and 0x18, as an example. If on a 16-bit EPROM we read only D0 to D7 (0x78), we’re completely missing all the data on D8 to D15 (0x18) – with each increasing address request from the SNES, we’re skipping every other 8 bits segment. In effect, on a 16-bit EPROM, A0 from the SNES should point to the bottom half (A0 = 0) or top half (A0 = 1) of each word. And therefore, A1 from the SNES is acting like the 27C322’s A0 pin. So all we have to do is shift the address pins from the SNES one position – A1 on the SNES is connected to A0 on the 322, A2 on the SNES is connected to A1 on the 322, etc. Then, we use the A0 pin from the SNES to control which half of the 16-bit word we read from. We can do this using a multiplexer.

A multiplexer is a device that is essentially a digitally controlled selector switch. In our case, we need eight separate switches to change between two different data lines all at the same time. D0 on the SNES should either read D0 or D8 from the 322 EPROM, D1 on the SNES should either read D1 or D9 from the 322 EPROM, and so on. When A0 from the SNES is 0, the multiplexer will route D0 to D7 from the 322 to the SNES, and when A0 from the SNES is 1, the multiplexer will route D8 to D15 from the 322 to the SNES. Make sense?

The 74HC257 is a quad-package two-line multiplexer. If we use two of them in parallel, we can control all eight data lines. So, you’ll want to follow this table to connect your cartridge, multiplexers and EPROM:

If your cartridge only has a 32-pin slot, then still follow the table above, but you’ll have to find alternate connections for A20 (A19, or pin 42 on the 27C322) and A21 (A20, or pin 32 on the 27C322). Follow A20 and A21 from the cartridge connector to somewhere you can solder onto. LoROM boards have A20 on pin 46, and A21 on pin 47 of the cartridge connector. HiROM boards have A20 on pin 45, and A21 on pin 46 of the cartridge connector.

So, find those pins, and follow the traces to an exposed solderable point on the board, and use that as your connection.

Here’s a schematic of how you’ll want to connect the multiplexers, if it’s easier for you to follow. I won’t include a schematic of where the EPROM pins go, since it’s a lot easier to just follow the left side of the table above.

When I went to wire this, I only had surface mount multiplexers lying around, but you can use through-hole for easier soldering. As I mentioned, I’ve only made reproductions with 27C322’s with my adapter boards, so I only have a picture of that here for reference.

Now, head to Step 10 and we’ll finish up the game.

Back to top of Step 9c

Step 9d: Install multiple 27C322 EPROMs on the donor board (ExHiROM)

If you’re going to make an ExHiROM game with 27C322’s, I’m going to recommend you use my 27C322 extended adapter. This will allow you to stack both of the EPROMs on top of each other and save a lot of extra wiring. But, if you really wanted to, you can just wire up the chips by themselves using the wiring specified on the product page.

Another disclaimer here is that I’m going to only give instructions on how to make this with HiROM boards that have one 36-pin ROM socket and a MAD-1 decoder. If you have a ‘139 decoder, or a HiROM board with multiple ROMs on it, I’m not going to cover it here, as they are less common or characteristic of more expensive games you shouldn’t be using as a donor! Remember, you can check your donor game out on SNES Central to see what kind of board it comes with.

There are a few pins you gotta take care of. Carefully bend up pin 13 on your two EPROMs, making sure not to flex them too much – they can be easy to break off if you’re not careful. I also recommend cutting off the thinner section of the pin to make it fit inside the cartridge better. Pin 13 is the /CE or chip enable pin. When this pin is driven to GND, the EPROM is allowed to make output. So what we’re gonna do with these two pins is alternate which EPROM is enabled using the MAD-1 decoder chip.

On the MAD-1, take it out of the socket and bend up pin 13, or carefully clip pin 13 and bend it up without taking the chip out. This pin is partially responsible for the output of pins 1 and 16. This is just one function of the MAD-1 decoder, and on boards with two ROM chips, pins 1 and 16 are normally tied to the /CE pins of each ROM to switch between the lower or upper ROM. Since our ExHiROM game is larger than 32 Mbit, the max size expected on normal HiROM boards, we need to change when pins 1 and 16 switch, so that the MAD-1 selects the lower or upper 32 Mbits.

Now, we should also disable the original ROM on the board, as is necessary with using the extended adapter boards. Cut pin 33, and solder the remaining pin connected to the original ROM to pin 34, like as seen here.

Ok, so now solder the extender adapter onto the board using the 36-pin ROM pins on the bottom of the board. You don’t have to worry about getting it perfectly flush against the donor board, because leaving a bit of extra room on the back might help the board fit nicer.

So now you should have your extender board in, with space above your donor board to fit the 27C322’s. How will we fit two, you ask? All we have to do is stack them on top of each other, making sure pin 13 on each do not touch. First, install your first EPROM in the 42-pin socket and solder it down. Then, stack your second EPROM on top of the first one and make sure it sits as close as possible to the first EPROM – this shouldn’t be hard as long as you don’t have too much solder on your pins. Then, solder the second one down on top of the first. Here’s what it should look like.

So, as the picture implies, you’ll be soldering wires now! Solder wires as follows:

EPROM #1 pin 13 to MAD-1 pin 1

EPROM #2 pin 13 to MAD-1 pin 16

MAD-1 pin 13 to Mask ROM pin 35

Make sure your wires don’t sit on top of the double-stacked EPROMs, otherwise your cartridge won’t close.

Now, it should fit in the cartridge ok. You might have to cut off a bit of plastic inside the cart, depending on how far your bent pins stick out, but the one I made fit alright.

The double stacked EPROMs sit directly on top of the plastic, as you can see, so that’s why we don’t want any extra wires on top of them. The cartridge edge sits nicely in the slot, but you can see a very slight tilt to the whole thing. This doesn’t actually make anything more difficult to fit in the cartridge slot though, it still fits just fine. That’s why I had mentioned having the adapter board sit farther up on the original ROM pins, to space it out away from the donor board, since there is a bit more room on the opposite side of the cartridge.

Great! Now, go ahead and skip to Step 10.

Back to top of Step 9d

Step 9e: Install one 29F033 EEPROM on the donor board

If you are using the one 29F033 chip, assuming the game programmed correctly your life is comparatively easier at this step. Just plop your little adapter board into the place where the other ROM was. Make sure you’re putting in the chip in the correct orientation!

You need to make absolutely sure your game is programmed correctly before you solder it into the socket. You don’t want to spend all that extra time desoldering a chip you found out was programmed incorrectly! Once you’re sure, go ahead and secure the header pins with solder and trim the bottoms off. In the picture below, the top row is uncut, and the bottom row is cut.

You can see the difference! Be careful when you’re clipping these – you don’t want one to fly into your eyeball. This has happened to me. It is not pleasant. Clip them into a trash can or something.

If your game only has 32 pins for the socket:

You will need to rewire pins 1, 2, 35, and 36 to their proper locations. You’ll also probably need to trim the bottoms of the pins off so that the other 32 pins still fit in the socket. Pin 1 is A20, pin 2 is A21, pin 35 is A22, and pin 36 is VCC. You can connect pin 36 to pin 34 with a jumper cable easily enough.

As for the other data pins, you’ll need to connect them to some other point on the board – this can vary depending on the board you have. All you have to do is find the correct pin on the cartridge connector, and follow the trace back to a solderable point. Hopefully there’s somewhere on the board you can connect to, but if there isn’t, you might have to solder onto the top of the connector. This should be pretty rare, though.

Depending on what kind of board you have, a LoROM or HiROM board, your A20, A21, and A22 pins will be on different parts of the cartridge connector! The only real difference is that for LoROM games, the normal A15 pin is skipped, and all the data pins are shifted by one. This also means that LoROM games don’t ever utilize A22. If you’re curious about why the pins are shifted, check out my SNES cartridge explainer, but I will not be getting into it here. But for our purposes:

LoROM has A20 on pin 46, and A21 on pin 47.

HiROM has A20 on pin 45, A21 on pin 46, and A22 on pin 47.

Now, go ahead and skip to Step 10.

Back to top of Step 9e

Step 9f: Install multiple 29F033 EEPROMs on the donor board (ExHiROM)

A short disclaimer here: I’m going to only give instructions on how to make this with HiROM boards that have one 36-pin ROM socket and a MAD-1 decoder. If you have a ‘139 decoder, or a HiROM board with multiple ROMs on it, I’m not going to cover it here, as they are less common or characteristic of more expensive games you shouldn’t be using as a donor! Remember, you can check your donor game out on SNES Central to see what kind of board it comes with.

The first thing you’ll need to do is remove your MAD-1 decoder from the PCB. Here’s what your board should now look like, and the components you’ll be using.

Bend up pin 13 on the MAD chip, and place it back into the board. If it’s easier for you, you can try just cutting the pin without removing the chip, but make sure you can still access pin 13 coming from the MAD-1 chip.

Now, remove pin 33 from the header on the FIRST EEPROM. This is the /OE (output enable) pin, which will be controlled by the MAD-1 chip. Put the EEPROM in the socket, making sure it’s in the correct orientation, and solder it in. Remember, you’ll be missing pin 33, so don’t solder anything on that. Do NOT trim the header pins on the back yet!

Now, you have one of two choices. If you want a cleaner looking assembly, remove the header pins on the SECOND EEPROM adapter board. Make sure all the solder is out of the holes, and place it on the back of the board on the header pins from the FIRST EEPROM, like a sandwich. Make ABSOLUTELY SURE the board is facing the exact same orientation as the first board so that pin 1 on “A” is connected to pin 1 on “B” and so on. You don’t want to put it in backwards or upside-down!!

If removing the header pins is too much of a pain for you (completely understandable), then you can connect each pin from EEPROMs “A” and “B” together with wires. But, make sure you do NOT wire the pin 33’s together!

Now, you should have a board with two TSOP adapter boards connected in parallel, either through wires or the sandwich method, with pin 33 disconnected to everything on both boards. You should also have a MAD-1 chip with a floating pin 13.

Connect pin 13 on the MAD-1 board to pin 35 on the TSOP adapter boards. Make sure both pin 35’s are connected! Then, run a wire from the “A” EEPROM pin 33 to pin 1 on the MAD-1 chip. Finally, run a wire from the “B” EEPROM pin 33 to pin 16 on the MAD-1 chip. Note that pin 1 and 16 on the MAD-1 chip are still in the board – this is because they’re not connected to anything on the board anyway, so we don’t have to pull them out. You can access them from the top of the board, or the back of the board. Here’s what it should look like afterwards (I used the sandwich method):

Now, you’re nearly done! Skip over to Step 10!

Back to top of Step 9f

Step 9g: Populate your custom PCB

Alternatively, you can view the quick guide if that’s your thing.

Depending on the board you have, you’ll need to do a few different things to get it up and running. Some boards might even ship with the necessary parts you’ll need to make your game. I’ll go over some of the common requirements for these boards, starting with the CIC chip.

As I mentioned earlier, the CIC chip is basically the region-locking chip. Every cartridge has one. It interfaces with a CIC chip on the SNES console to check and make sure the region is correct. So any game we make is gonna need one itself. If you’ve got an extra one from an old game lying around, you can use that, but there’s a way to make one from a microcontroller. All we have to do is program a PIC12F629 with the “SuperCIC” code from the SD2SNES blog (based on the work from Segher at HackMii). Luckily, the MiniPro programmer we have has the capability to program the PIC. Follow the instructions on the site if you’re not sure how to program this correctly.

You shouldn’t run into too many problems, it’s a pretty simple process.

Using My Custom PCB (SNES Mask ROM)

If you’re using my 27C322 board instead, skip ahead to this section.

A lot of the board is self explanatory. Here’s what the front of the board looks like:

So, easy things first. The CIC chip we just programmed above goes on the bottom left of the board. C1 is for the electrolytic capacitor – these were 22 uF on the original SNES boards, so something around there should be sufficient (make sure it’s rated for at least ~10 V or higher). C2 and C4 should be used in all situations, I use something around 0.1 uF – these are to filter out any electrical noise that could corrupt data.

If your game uses any kind of SRAM, you’ll need to populate the rest of the board. The SRAM chip goes up on the top right of the board. I included sockets for the common “slim” package and the “wide” package SRAM chips. The board supports the 64 Kbit SRAM chips (6264 series). If you’re using the slim packages, make sure you use the bottom and middle rows of through holes. Also, be sure to populate C3 similar to C2 and C4. You’ll need a ‘139 decoder chip as well (like the 74HC139 – I have the surface mount package on the board, which is fairly easy to solder). Finally, the battery should be installed and R1, RE, RB, D1, and D2 as well. I use ~1 kΩ for R1 and RE, 10 kΩ for RB, and small 1N914 diodes for D1 and D2 – make sure to get the polarity correct! You’ll also need an NPN transistor like the 2N2222.

Now let’s take a look at the back of the board.

The most important part of this board are the 3-way jumper pads on the bottom right. You need to add a solder bridge to every one (from the middle pad to either the left or right) based on if your game is a HiROM or LoROM bank type. They’re pretty close together so it shouldn’t be hard to bridge them with solder, but if you’re having trouble, you could use a bit of wire too. If your game is LoROM with no SRAM, you additionally need to bridge all three pads together on the bottom right set of pads.

If your game uses SRAM, solder the jumpers in the top middle based on how large the SRAM is. For example, if your game uses 64K SRAM, bridge the top two right pads, and the bottom two left pads. Don’t forget to bridge the pads on the left as well if you’re using SRAM.

The three pads on the bottom left of the board need to be soldered together when you put the game in. The reason I added these pads here is if you desolder the two pads, and you leave the header pins on a 29F033 adapter board sticking out long enough from the back of the socket, you can reprogram the EEPROMs using the TL866 adapter board. Neat!

Finally, the EPROM or EEPROM of your choice should be assembled in the Mask ROM socket. If you’re using the 27C801 EPROM, be sure to kink out the two legs indicated and solder them there instead. Now, skip to Step 10.

Using My Custom PCB (27C322)

This board is very similar to the SNES Mask ROM board. Here’s the front:

So, easy things first. The CIC chip we just programmed above goes on the bottom left of the board. C1 is for the electrolytic capacitor – these were 22 uF on the original SNES boards, so something around there should be sufficient (make sure it’s rated for at least ~10 V or higher). C2 and C4 should be used in all situations, I use something around 0.1 uF – these are to filter out any electrical noise that could corrupt data.

If your game uses any kind of SRAM, you’ll need to populate the rest of the board. The SRAM chip goes up on the top right of the board. I included sockets for the common “slim” package and the “wide” package SRAM chips. The board supports 64 Kbit SRAM chips (6264 series). If you’re using the slim packages, make sure you use the bottom and middle rows of through holes. Also, be sure to populate C3 similar to C2 and C4. You’ll need a ‘139 decoder chip as well (like the 74HC139 – I have the surface mount package on the board, which is fairly easy to solder). Finally, the battery should be installed and R1, RE, RB, D1, and D2 as well. I use ~1 kΩ for R1 and RE, 10 kΩ for RB, and small 1N914 diodes for D1 and D2 – make sure to get the polarity correct! You’ll also need an NPN transistor like the 2N2222.

Now let’s take a look at the back of the board.

The back is a bit busy, but it’s nothing terribly complicated. The first thing you should populate are the ‘257 multiplexers needed with the 27C322 EPROM. I generally use the 74HCT257 multiplexers, but any 257-type chip will work fine. Please note these are surface mount! (On newer versions of the board, these will be located on the front of the board.)

The most important part of this board are the 3-way jumper pads on the bottom right. You need to add a solder bridge to every one (from the middle pad to either the left or right) based on if your game is a HiROM or LoROM bank type. They’re pretty close together so it shouldn’t be hard to bridge them with solder, but if you’re having trouble, you could use a bit of wire too. If your game is LoROM with no SRAM, you additionally need to bridge all three pads together on the bottom right set of pads.

If your game uses SRAM, solder the jumpers in the top middle based on how large the SRAM is. For example, if your game uses 64K SRAM, bridge the top two right pads, and the bottom two left pads. Don’t forget to bridge the pads on the left as well if you’re using SRAM.

Now, just put your 27C322 EPROM into the socket, and you’re good to go!

Back to top of Step 9g

Step 10: Finish your game

When you put your board back in the cartridge, you might have to clip the little plastic stand-off on the back of the cartridge, especially if you used the TSOP adapter board because that’s gonna get in the way.

Now close your game back up nice and tight. If you did everything right, you should be playing your game just fine! If not…. well here’s a few things you can try to fix it.

Troubleshooting tips

If you’re reading this section to fix a game, you should heed my earlier advice if you haven’t already, and invest in making a dedicated prototyping board with proper sockets for things like your EPROM. I have a few special boards set aside with these sockets so I can swap these chips in and out to test games before I solder them directly to the board. They are extremely handy. It’s pretty easy to make some test boards using my custom PCBs, so check them out if that sounds like something you’d like to try.

If you’re using a donor cartridge, before you try anything, check to see if your game is LoROM bank type, uses SRAM, and has the ‘139 decoder. If this applies to you, try taking the ‘139 decoder out and rewiring as such:

If this is the case for you, except your board is HiROM, let me know and I’ll look at the wiring. The only boards I know that would fit this description for HiROM games are expensive ones that you probably aren’t using as donors, but I might have missed one.

If this doesn’t apply to you, here’s some tips you should follow before you give up. This is the order I would try them in – it’s listed from shortest to longest amount of time to check. Please do these things before you message me or leave a comment, cause I’m gonna ask you if you did before anything else!!

Check for any cold solder joints. They’ll be recognizable by their “misty” or “crumbly” appearance. To fix them, just heat them up (and make sure they’re heated sufficiently) and put some new solder on them.

Also, make sure you didn’t miss any pins or wires. You’ll have a lot to solder, after all. It only takes a single pin to be disconnected to screw up the whole thing.

Make sure your SNES works with other normal games. I know this sounds silly, but you never know if your SNES just kicked the bucket or not between games. I once bought Super Mario RPG and the sound didn’t work – but it wasn’t the game, it turns out my SNES audio fried since I last played!

Check to make sure all your chips are in the correct orientation – especially for custom PCBs, where you have to provide many chips yourself.

Check to make sure you didn’t cut any traces on the board accidentally – if you did, you’ll have to add a replacement wire.

If you’re using a donor, did you remember to test the original game before you took the EPROM out? Maybe something else is damaged on the board, and it’s not your fault. Try replacing the capacitors (smaller ones are 0.1 uF, the large electrolytic is 22 uF). Clean the contacts that go into the SNES on the cartridge. Use like rubbing alcohol or something, look online for resources, I’m not good at housekeeping stuff.

Finally, even if you THINK everything is connected correctly, use a multimeter and check the continuity of each pin on your EPROM or other chips to its destination. This means testing the cartridge connector in some cases. Follow the pin tables and/or schematics for the type of memory chip you chose up in Step 9. This is arduous – but any time I was stumped, I usually found that just one of the pins I thought was connected wasn’t in reality. Refer to this table below for the pinout of the cartridge – you only really have to test the address pins (A0 – A23), data pins (D0 – D7), GND and Vcc pins. Everything else should have been left alone.

If all else fails, you might have to desolder your chip, blank it, reprogram, and try again. Unfortunately, it’s hard to troubleshoot these boards sometimes.

Make a label

First things first, if you’re using an existing cartridge, you gotta get that old pesky label off of your game. You’re gonna want to just focus on the front cover, obviously. You can try to take the label off by hand, but I’ve never been able to get it completely off. Always get a ton of extra residue and paper.

I found a solution that works pretty well, though. All you have to do is mix equal amounts of baking soda and vegetable oil – you only need about a tablespoon. Rub it on all the leftover sticker and let it sit for half an hour. Afterwards, scrub it clean with some steel wool or your fingernails or whatever, it should come off pretty easily. Wash it off and you should have a blank canvas on which to work. I’ve also seen that soaking the cartridge in water for an hour or two will make the paper soft, and you can rub it off with your fingers.

Now, you need to get a new sticker for the front! You can either buy them online at various shops for $5 or $6, which might be the most convenient for you, or you can print them yourself if you have a good enough printer (or if your game doesn’t actually have a label). It might be cheaper to just buy them individually if you’re not planning on making a whole lot of games. Maybe see if your local office supply stores sell these in single sheets or will print them on the paper for you?

If you want to make your own label, use this template. I found it on DeviantArt.

Then, you can use your favorite photo editing software (I prefer GIMP, which is a free Photoshop-esque program) to place your own picture and name. Search for pictures of your game on Google or something as a reference.

Now, you’ll want to make sure the size matches up for when you print them out. The SNES labels need to be approx. 1.77” x 3.25” when cut. I’m not a wizard at getting this to line up correctly, so you’re on your own for this.

You can use full page sticker sheets and cover them with lamination paper. It’s more economical to fill up a whole sticker sheet with labels, then cover it with a full sheet of lamination. Buying a full package of these sticker and lamination sheets can get a bit pricey, though. A suggestion from mrTentacle is to print the label on vinyl sticker sheets, then spray them with a fixative. The sticker sheets he uses are similar to these and the finish material is similar to this.

Back to top of Step 10

Conclusion

It’s been a long time coming, but finally, you’ve completed your first SNES game! Feeling good about yourself? You should be!

Remember that selling reproductions of licensed games is illegal! I do not condone this! And don’t go to conventions trying to sell them, passing them off as legitimate! That’s called being a jerk. Don’t rip off genuine game collectors, we’re nice people. I can’t tell you how many times I’ve bought games on eBay or in a store that I thought was genuine, and it turned out to be a reproduction. It shouldn’t happen!

Hopefully this guide was comprehensive and detailed enough to give you a good understanding of what to do and why we did it. If any part is unclear, if I have any mistakes, or you need help figuring out your board, feel free to email me, and I will do my best to clarify or fix the problem! I still plan on continuously updating this tutorial but let me know what you wanna see most, and I’ll try to focus on that if there’s enough of a demand!

Until then, tinker on my fellow hobbyists!

I got a lot of my information from the NesDev forums (RIP NintendoAge). Check them out – they’re amazing! Also, special thanks to Michael at AmpereSandRepros for his board donations, and Martin Samuelsson (mrTentacle) for his board and chip donations and for helping myself and others in the comments section.

And if you’d like to purchase any of my materials, head over to the store page and I’ll be happy to hook you up!

Back to top