Interactive Connector Diagram
Click or tap any pin in the diagram below to inspect its signal assignment, electrical specification, and wire colour standard.
Click any pin to view its signal assignment, electrical spec, and wire colour.
Supported Systems / Found On — Retro Machine Hubs
This connector is used on the following retro computer systems. Click any colour-coded badge below to open its full board-level repair, diagnostic, and schematic Machine Hub:
Connector Specifications
Logic Level
3.3 V CMOS (Use 74LVC245 or bi-directional MOSFET shifters when interfacing with 5 V TTL!)
Strapping Pins
GPIO0 (Must be High for normal boot), GPIO2 (Low for flash), GPIO12 (MUST be Low at boot!), GPIO15
Input-Only Pins
GPIO34, GPIO35, GPIO36 (VP), GPIO39 (VN) — No internal pull-ups or output drivers!
Forbidden Pins
GPIO6 to GPIO11 are hardwired to the internal SPI Flash chip — never connect!
Full Pin Assignment & Wiring Reference
| Pin | Signal Name | Direction | Electrical Spec / Role | Wire Colour / SCART / Adapter Target |
|---|---|---|---|---|
| GPIO0 | BOOT / STRAPPING | I/O | Strapping Pin (Internal Pull-Up: High = Run Flash; Low = Serial Bootloader) | BOOT Button |
| GPIO1 & GPIO3 | UART0 TX (1) & RX (3) | I/O | USB-Serial Console TX0 (GPIO1) and RX0 (GPIO3) | USB UART0 |
| GPIO2 | ONBOARD LED / STRAP | I/O | Onboard Blue LED (Must be Low or Floating during serial flashing) | Blue LED |
| GPIO4, 16, 17 | UART2 RX (16) & TX (17) | I/O | Safe General Purpose I/O & Hardware UART2 (Ideal for Zimodem / SIO!) | Safe GP I/O |
| GPIO5, 18, 19, 23 | VSPI (SD Card Bus!) | I/O | Default VSPI for MicroSD Cards: CS=GPIO5, SCK=GPIO18, MISO=GPIO19, MOSI=GPIO23 | SD Card SPI |
| GPIO12 (MTDI) | VDD_SDIO STRAP TRAP! | I/O | WARNING: Must be LOW (0 V) at boot! Pulling High selects 1.8V Flash and crashes! | Keep Low at Boot |
| GPIO13, 14, 15 | HSPI / JTAG PINS | I/O | Secondary HSPI bus (SCK=14, MISO=12, MOSI=13, CS=15) | HSPI |
| GPIO21 & 22 | I²C SDA (21) & SCL (22) | I/O | Default I²C Bus (for SSD1306 OLED displays on FujiNet / Tapuino) | OLED I²C |
| GPIO25, 26, 27, 32, 33 | SAFE GP I/O + DAC | I/O | Safe General Purpose I/O + 8-Bit Analog DACs (GPIO25 & GPIO26) + ADC1 (32/33) | Safe GP I/O |
| GPIO34, 35, 36, 39 | INPUT ONLY (No Pullup) | In | INPUT-ONLY Pins (Great for reading buttons/status; require external pull-up resistors!) | Input Only |
| VIN, 3V3, GND | 5V IN / 3.3V OUT / GND | Pwr | VIN = +5 V Input (to AMS1117-3.3); 3V3 = Regulated +3.3 V Out; GND = 0 V | Power Rails |
Best Practices When Connecting an ESP32 to 5V Retro Computers
The ESP32-WROOM-32 DevKit V1 is the powerhouse behind modern retro wireless and storage interfaces (FujiNet for Atari/Apple/Coleco, BlueRetro Bluetooth joystick adapters for Amiga/C64/Atari, Zimodem User Port/RS-232 Wi-Fi modems, and TRS-IO for the TRS-80). Knowing which pins are safe general-purpose I/O versus boot-strapping or input-only pins avoids hours of debugging.
- Always Use UART2 (GPIO16 RX2 & GPIO17 TX2) for Retro Serial Links: Leave GPIO1/GPIO3 (UART0) free for USB debugging and firmware updates, and remap your retro serial bus (Atari SIO, C64 User Port, or MAX3232 RS-232) to GPIO16 and GPIO17 in hardware!
- Why ADC2 Pins Cannot Read Analog Joysticks When Wi-Fi Is Active: On the ESP32, the internal ADC2 controller (GPIO0, 2, 4, 12–15, 25–27) is shared with the Wi-Fi radio! Always use **ADC1 pins (GPIO32, 33, 34, 35, 36, 39)** for reading analog paddles or voltages while Wi-Fi/Bluetooth is running.