Nes discrete mapper 1-1

Nintendo Entertainment System (NES) Discrete Mapper Cartridge

This is an updated design of my old NES Discrete cartridge boards. Functionally, this design is nearly the same as the older one, but I added compatibility for a few new mappers and expanded the available memory for some mapper types, and under the hood I have ported the project over from Eagle to KiCad and heavily cleaned up the schematic and some of the trace routings. This version is also fully open source!

This circuit board can be used to make most NES cartridges that rely on discrete logic chips to operate. These boards are most common in the earlier NES releases. The following mapper types are supported (click the link to view the games that use that specific mapper):

There are a handful of more obscure mappers supported as well:

For Replacing Damaged Circuit Boards

This board can be used as a drop-in replacement for damaged original NES cartridge circuit boards - but only for NROM and CNROM games. This means you can take the chips off of the damaged circuit boards (assuming the chips are still in good condition) and solder them into this board. You may need to replace the capacitors if they are damaged. You still need to configure the board for the mapper you wish to use with the solder pads, and bend out pin 28 on the PRG Mask ROM, as detailed in the section below.

If you wish to use this board to replace damaged circuit boards for other mapper types (such as AxROM or UxROM), you can transfer over the logic chips and CIC, but will need to do some manual rewiring of the Mask ROM chips, which I will not be detailing in this repository. Refer to this page on the Nesdev wiki and cross-reference with board schematic if you wish to figure it out for yourself. It will involve bending specific pins on the Mask ROM up so they are not inserted into the sockets on the board to be rewired elsewhere.

Important Things Before You Start

1. Please review the wiki for more information about using the circuit boards, instructions for how to program them, and example builds.
2. When soldering parts on, it's a good idea to put kapton tape or otherwise cover the bottom cartridge edge. You do not want to get solder on the cartridge contacts.
3. I am not responsible for any damage you do to your self or your property. Attempt this project at your own risk.
4. I do not guarantee design compatibility. You may encounter issues with certain games. There is also a chance I have made an error in the design or the BOM - if this is the case, I will do everything I can to address the problem as quickly as possible.
5. If you are using this board to make games other than for personal use, you must have permission from the originator to use and distribute any ROM images or other related material. You are responsible for making sure you adhere to any license requirements.

DO NOT use my circuit boards for profiting from stolen work - this especially includes homebrew content, ROM hacks, and using fan-made labels without permission from the originator. Support ALL original creators!

Board Characteristics and Order Information

The zipped folder contains all the gerber files for this board. The following options must be chosen when ordering boards for yourself.

• Thickness: 1.2mm
• Surface Finish: ENIG
• Gold Fingers: Yes, 30° chamfer

You can use the zipped folder at any board fabricator you like. You may also buy the board from PCBWay using this link (disclosure: I receive 10% of the sale value to go towards future PCB orders of my own):

Purchase from My Website

You can purchase this circuit board at my website, https://mousebitelabs.store. Click the following image to be directed to the specific item listing:

Purchase from Etsy

I also offer the board on Etsy, if you would rather purchase through there - click the banner to be redirected.

Required Equipment

• You will need basic tools, like a soldering iron.
• You need a way to program the ROM chip(s). For NES games, I usually use the T48 programmer.
• If you do not have an original CIC to transfer to this board, or a region unlock mod on your console, you will need an ATTINY13 with the AVRCIC code by krikzz to fake out the lockout chip. You will need a way to program these chips. I use the T48 to do so, but you can also use something like the PICkit 3. Be sure to see the tutorial on how to program these lockout chips, as you need to change a few settings before programming the code.

How to Program the Game and CIC

For a tutorial on how to prepare and program the ROM file(s), please check out this wiki page.

For a tutorial on how to program the CIC code onto the ATTINY13 if you do not have an original CIC to use, please check out this wiki page.

Board Configurations

This board is highly customizable. You do not need every single part on this board to make a game. The cartridge configuration you need for the game you want to make is mainly dependent on the mapping type. Depending on your needs, you only need to solder on certain components, which you can find below in the BOM section. You will also need to configure the game with the various solder jumpers on the back of the board.

I highly recommend checking out the various examples of board configurations on the wiki.

Solder Jumpers

This board is rife with solder jumpers. Sorry! That's the cost of making a single board that can cover many different configurations. Not all jumpers need to be soldered, depending on the game you're making. Again, I highly recommend checking out the various examples of board configurations on the wiki. That will give you a shortcut for most solder jumpers, other than the mirroring jumpers, which are detailed in this next section.

On the back of the board, you will see a legend for decoding what jumpers need to be soldered (this legend also tells you if you need ROM or RAM for the CHR component):

Basically, follow this for your selected mapper. Anywhere you see "A" next to a jumper, bridge it with solder for AxROM games; for BNROM, look for "B"; etc. The exception to this is NROM - this requires no solder jumpers to be soldered, except for the mirroring jumper and the ROM /OE jumpers on the front of the board (indicated by "OTHERS").

ROM /OE Selection Jumpers

On the bottom right-hand side of the front of the board, you will see two sets of two-way jumpers:

The "OTHERS" in this case refers to "other" mappers other than AxROM or UxROM (including NROM).

Solder them like this for AxROM games:

And this for UxROM games:

And this for all other mappers:

Mirroring Jumpers

These jumpers need to be set for every game EXCEPT for AxROM games (AMROM, ANROM, AN1ROM, and AOROM) which require you to NOT solder these pads. If you do not set these pads properly for non-AxROM games, you will experience graphical issues. If after you make a game and you are experience graphical issues, but gameplay still works, then it might be that you set these pads wrong.

Each non-AxROM game needs to be set for Horizontal (V) or Vertical (H) mirroring. Yes, I know the letters are flipped, and there is a reason for that, but I'm not going to spend time explaining the details behind it. The main thing you need to know is that if you're making a game and you use the FamiROM tool (that is explained in the ROM preparation section of the wiki), it will report the ROM information on the box that pops up. Check the "mirroring" value. In this example, Elevator Action, it reports the mirroring as Horizontal.

Now, check out the PCB (courtesy of NesCartDB):

See that the "V" pads are bridged. This is why my board shows both the nomenclature FamiROM reports and the letter that appears on the original PCB for the games.

Selecting U4

U4 is the main mapping chip for all board types except NROM (which does not need one). U4B and U4C are 74'161 that have four sets of I/O, and U4A is the 74'377 which has eight. These I/O are connected to the data pins (D0-D7). If you're making a CNROM or UxROM game, you can use a 74'161 in the U4B socket; if you're making AxROM or BNROM, you can use a 74'161 in the U4C socket.

If you use the 74HCT377, you can achieve an "expanded" version of CNROM, UxROM, AxROM, and BNROM. This expanded memory has no functionality for games that do not use it - this feature is more for developers to take advantage of. One exception to this is Panesian games - these utilize the expanded CNROM mapper type, and therefore require the 74'377.

If you want an easy option to cover all your bases without having to think too hard about what chip to use, I recommend simply populating U4A (74HCT377).

PRG ROM Considerations

I use the 39SF040 NOR Flash chips for all my ROM needs - they're new, easily available, and cover all your bases for NES games - but there are plenty of other options that can be used, like the 27C UV EPROMs (27C256, 27C512, 27C010, 27C020, 27C040, and 27C080). Whatever chip you select, it must be large enough to hold your ROM file (again, see the ROM preparation section of the wiki).

If you use the 27C040 or 27C080, then you need to solder these pads on the back:

If your ROM chip is only 28 pins (like 27C256 and 27C512, or the original PRG Mask ROM if you are using the board as an NROM or CNROM replacement) you need to bend out pin 28 and solder it to the alternate hole labeled DIP28, shown here:

Special Mapper Types

There are a few special cases for a few obscure mapper types that this board supports:

• For making Panesian games, follow instructions for a CNROM board type, but you must use U4A.
• To achieve Mapper 180, follow instructions for a UxROM board type, but replace the 74'32 with a 74'08. See the BOM for more information.
• To achieve Mapper 87, follow instructions for a CNROM board type, but you must use U4A with pins 5 and 6 bent out to solder to the adjacent pins from the U4B footprint.
• To achieve Mapper 79 or 148, follow instructions for a CNROM board type, but you must use U4B with pin 11 bent inward under the part footprint to solder to the test point.

Once again, again, I highly recommend checking out the various examples of board configurations on the wiki where this is also covered.

Troubleshooting

Please check out the wiki pages for troubleshooting tips.

Bill of Materials (BOM)

NOTE 1: The 39SF040 is listed as the recommended part for all of the following BOMs - it will cover any and all games, but you can also use the following chips if they are big enough for the game file you have:

• UV EPROM: 27C256, 27C512, 27C010, 27C020, 27C040, 27C080
• NOR Flash: 39SF512, 39SF010, 39SF020

NOTE 2: The AS6C6264 is recommended for the CHR RAM for boards that require it, but the AS6C62256 also works.

All games will require the following parts:

* This can be harvested from an original NES game (this is not needed if you have region modded your NES)

** Not needed if U2 is a 28-pin UV EPROM.

NROM

These extra parts are required for NROM games:

UxROM

These extra parts are required for UNROM and UOROM games:

* Use either U4A/C4A OR U4B/C4B. Do not use both!

Special note: For Mapper 180, replace U5 with 74HCT08 (https://mou.sr/3AM08eK)

CNROM

These extra parts are required for CNROM games:

* Use either U4A/C4A OR U4B/C4B. Do not use both!

Special note: Panesian and Mapper 87 games require U4A/C4A, Mapper 79 and 149 games require U4B/C4B.

AxROM

These extra parts are required for AMROM, ANROM, AN1ROM, and AOROM games:

* Use either U4A/C4A OR U4C/C4C. Do not use both!

Color Dreams

These extra parts are required for Color Dreams games:

BNROM

These extra parts are required for BNROM games:

* Use either U4A/C4A OR U4C/C4C. Do not use both!

GNROM

These extra parts are required for GNROM games:

Sprite Glitch Resistors

In rare cases, you might encounter some sprite glitching even if everything is configured properly. This usually only happens when you have things like a Famicom-NES adapter or Game Genie in your system that artificially lengthen the connections from the cartridge to the console. It also can depend on the type of console you're using. What sets this aside from other graphical glitches is that it affects the sprites, not the entire screen. So if you’re getting strange palettes, missing backgrounds, or weird tiles, your problem is something else, probably a bad cartridge connector or dirty cartridge edge. What you’ll see if you’re getting this kind of error, known as OAM corruption, looks something like this (click the picture to view a video):

Fixing this error involves adding ~100 ohm resistors (like these: https://mou.sr/4o1seJo) in series with the PRG D0 to D7 lines. This can be done by cutting the exposed traces in the middle of RD0 to RD7 with a blade, and soldering resistors in place (surface mount size 0603). Be careful not to cut other parts of the board (or yourself).

(These pictures are from another board, but they are present on this board as well.)

Considerations for v1.0

On v1.0, mapper 79 and 148 are not supported. (That shouldn't affect most users)

If you are using a 27C040 or 27C080 for the PRG ROM, you must bend up pin 1 before placing it into the PRG socket. Then, solder a wire from the bent-up pin and connect it to pin 31.

Revision History

v1.1 - Release

• Added pad for using 27C040 and 27C080 PRG EPROMs.
• Fixed Mapper 079/148 instructions and added extra test point for proper configuration.

v1.0 - Prototype

Acknowledgements and Resources

• The Nesdev wiki was indispensible for making this board, especially this specific page by lidnariq.
• NesCartDB has a wealth of images and information about the vast majority of the NES library. I've used it for years, it helped me create these boards, and I suggest you do too for referencing specific games.
• Continual thanks to all in the nesdev community for their resources, design tips, and support throughout the past half-decade.

License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. You are able to copy and redistribute the material in any medium or format, as well as remix, transform, or build upon the material for any purpose (even commercial) - but you must give appropriate credit, provide a link to the license, and indicate if any changes were made.

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