Just Enough WonderSwan Color/Swan Crystal EEPROM dumper

⚠️ USE WITH CAUTION! Always test on a handheld of lesser importance to confirm its operation

On each boot the bootrom writes to the EEPROM, removing the authenticity of the factory default. Such writes include the "unique" cartridge count, boot count, and previously booted cartridge identifier. If these are not important, a custom rom and serial cable is the more convenient alternative, eg. https://github.com/asiekierka/ws-ieepview

Fun Fact: The SwanCrystal EEPROM contains the Bandai bootsplash present in the bootrom.

Components

Shop around, AliExpress links are non-affiliated top searches.

• 1x Blue Pill [AliExpress]
• 1x ST-Link¹ or USB to TTL² [AliExpress¹ or AliExpress²]
• 1x SOP8 Test Clip [AliExpress]
• 1x Breadboard [AliExpress]
• 7x Male to Male Dupont Cables [AliExpress]
• 1x 1.2K Resistor [AliExpress]

Arduino Bootloader

There are nemerous guides on how to install the STM32duino bootloader and the following video does an excellent job of describing the process.

Additionally, you may require the STM32 Virtual COM Port Driver.

Wiring

Blue Pill	Test Clip	EEPROM
A4	1	CS
A5	2	SK
A6	3	DI
A7	4	DO
G	5	GND
3.3	8	VCC

1.2K pull-down resistor connected to pin 1 (Chip Select) and pin 5 (Ground) of the test clip.

Optional: 1.5K pull-up resistor connected to pin 4 (DO) and pin 8 (VCC) of the test clip.

Cape

Usage

1. Upload the Arduino sketch and run the Arduino IDE Serial Monitor or any alternative serial terminal such as Tera Term or Putty.
2. Send an r character to read the EEPROM.
3. Select all and copy the hex output.
4. Paste the copied hex output as hex into a Hex Editor such as https://hexed.it/ or HxD
5. Save As...

Testing

Higan is able to load and emulate your EEPROM dump by renaming it as save.eeprom and moving it into the Systems/WonderSwan Color or Systems/SwanCrystal directories.

Custom Bootsplash

WonderSwan Color

https://github.com/up-n-atom/higan/tree/ws-bootsplash/higan/System/WonderSwan%20Color

• Dengeki
• NAVI GET 400 Million
• MS-06S Zaku II
• RX-78-2
• Inuyasha
• Growlmon

SwanCrystal

https://github.com/up-n-atom/higan/tree/ws-bootsplash/higan/System/SwanCrystal

• One Piece Grand Battle Swan Colosseum
• Tanita Mama Mitte