Accessory port pinout

The WonderSwan accessory (EXT) port provides:

• 3.3V power delivery to the peripheral,
• an UART serial port,
• an I²S digital audio output.

Note that the UART uses inverted polarity.

Pinout

(Female 8-pin port on peripheral)

       MISO_          _MOSI
            \        /
      +3V_   \      /   _GND
    ______\ __\ __ /__ /______
   |      04__03__02__01      |
   |   __|""  ""  ""  ""|__   |
   |  |__                __|  |
   '.    |..__..__..__..|    .'
     \____05__06__07__08____/
         _/   /    \   \_
     BCLK    /      \    /HDPN
           _/        \_
       LRCK            SDAT

Pin	Group	Description
01 (GND)	Power	Ground
02 (MOSI)	UART	WonderSwan -> Accessory
03 (MISO)		Accessory -> WonderSwan
04 (+3V)	Power	3.3 volt?
05 (BCLK)	I2S	Bit clock
06 (LRCK)		Channel clock
07 (SDAT)		Bit data
08 (/HDPN)		Headphone detect

HDMI connector mapping

Luckily, it turns out that male HDMI connectors are somewhat electrically compatible with male EXT port connectors. This allows repurposing them as a replacement for a female EXT port connector.

• Note that using an HDMI plug may cause increased wear on the connector.
• In addition, an HDMI plug lacks the plastic sleeve which the original EXT port connector has, which leads to a loose connection.
  • One solution is to 3D-print a sleeve to improve connection.
  • Another solution is to include some type of LED/indicator in order to validate proper connection.

Due to the lack of availability of new EXT port connectors, this is a popular solution among DIY users and lower-end aftermarket accessories.

HDMI pins connect to EXT port pins as follows:

EXT	HDMI
01 (GND)	15 (SCL)
02 (MOSI)	11 (TMDS Clock Shield)
03 (MISO)	7 (TMDS Data 0 +)
04 (+3V)	3 (TMDS Data 2 -)
05 (BCLK)	4 (TMDS Data 1 +)
06 (LRCK)	8 (TMDS Data 0 Shield)
07 (SDAT)	12 (TMDS Clock -)
08 (/HDPN)	16 (SDA)