NES-DEV-CART

Open-source FPGA development cartridge for the Nintendo Entertainment System.

Plugs into a real NES. Programs over USB-C. Debug via UART. Full NES bus access.

What Is It

NES-DEV-CART is a cartridge-shaped PCB that replaces the ROM chip with a modern FPGA. It gives your FPGA bidirectional access to every signal on the NES 72-pin cartridge connector — CPU bus, PPU bus, CIC, expansion port — all level-shifted between 5V and 3.3V.

An onboard FT2232HL provides USB-C JTAG programming and UART debug console. No external programmer needed.

Specs

FPGA	Sipeed Tang Primer 25K (Gowin GW5A-25, 25K LUTs)
ROM Storage	8MB SPI PSRAM
USB	FT2232HL — Ch.A: JTAG, Ch.B: UART debug
Level Shifting	4x 74ALVC164245DGG (bidirectional 5V-3.3V)
NES Signals	CPU A0-A14, D0-D7, PPU A0-A13, D0-D7, CIC, IRQ, EXP
PCB	4-layer, 1.6mm, ENIG, gold fingers, L-shaped
Connector	72-pin NES edge connector (30-degree bevel)
FPGA Connection	2x DF40C-60DS 0.4mm B2B connectors

What You Can Build

• Homebrew games — test on real hardware, not emulators
• Custom mappers — design mapper chips in Verilog that never existed
• Flash cartridge — load ROMs from USB, run on real NES
• Bus analyzer — sniff CPU/PPU traffic in real time via UART
• Expansion audio — VRC6, Sunsoft 5B style audio hardware
• Hardware research — study NES bus behavior at the signal level

Repository Structure

hardware/
├── nes-dev-cart.kicad_pcb      KiCad PCB layout
├── nes-dev-cart.kicad_sch      KiCad schematic
├── nes-dev-cart.kicad_pro      KiCad project
├── footprints/                 Custom footprint libraries
└── production/
    ├── nes-dev-cart-gerbers.zip    Fabrication-ready gerbers
    ├── nes-dev-cart-bom.csv        BOM with LCSC part numbers
    ├── nes-dev-cart-cpl-jlcpcb.csv Component placement list
    ├── README-assembly.md          Assembly instructions
    └── gerbers/                    Individual gerber files

website/                        Product website

Ordering PCBs

Upload hardware/production/nes-dev-cart-gerbers.zip to JLCPCB:

• Layers: 4
• Thickness: 1.6mm
• Surface finish: ENIG
• Gold fingers: Yes, 30-degree bevel
• Assembly: Both sides (DF40 connectors on bottom)

Upload nes-dev-cart-bom.csv and nes-dev-cart-cpl-jlcpcb.csv for SMT assembly. See production/README-assembly.md for details.

Requirements

• NES front-loader console (NES-001)
• Sipeed Tang Primer 25K module
• USB-C cable
• Gowin IDE or Yosys/nextpnr for FPGA development

License

Hardware: GPL-3.0

NES-DEV-CART is an independent project not affiliated with or endorsed by Nintendo.

Links

• Website: https://nesos.dev