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ESP32 pinout & GPIO reference
The original ESP32: highest shipping volume and the deepest documentation. GPIO 6–11 are taken by internal flash, GPIO 34–39 are input-only, and ADC2 is unavailable while Wi-Fi is active — the three traps every newcomer hits.
Data verified：2026-10-20 · Cross-checked against Espressif datasheets and the ESP-IDF programming guide. Always confirm with the official document before finalizing a design.
Official documentation：link 1
Key specifications
| Core | Xtensa LX6 dual-core (+1 ULP co-processor) |
|---|---|
| Clock | 80 / 160 / 240 MHz configurable |
| SRAM | 520 KB |
| Wireless | Wi-Fi 802.11 b/g/n · Bluetooth 4.2 + BLE |
| USB | No native USB — external USB-UART bridge required |
| ADC | 2 × 12-bit SAR, 18 channels total |
| DAC | 2 × 8-bit (GPIO25 / GPIO26) |
| Touch | 10 capacitive touch channels |
| GPIO | 0–39 (~26 actually usable) |
| Security | Secure Boot · Flash encryption · AES/SHA/RSA acceleration |
Traps that cost you a board respin
- GPIO 6–11 connect to the internal SPI flash and must never be used as ordinary GPIO.
- GPIO 34 / 35 / 36 / 39 are input-only and have no internal pull-up.
- ADC2 (GPIO 0/2/4/12–15/25–27) is occupied while Wi-Fi runs — use ADC1 instead.
- GPIO 12 (MTDI) is a strapping pin: pulling it high changes the boot voltage. Check it first when boot fails.
Full GPIO table
| GPIO | Status | Alternate functions |
|---|---|---|
GPIO0 | Usable | ADC2_CH1TOUCH1 |
GPIO1 | Usable | UART0 TX |
GPIO2 | Usable | ADC2_CH2TOUCH2 |
GPIO3 | Usable | UART0 RX |
GPIO4 | Usable | ADC2_CH0TOUCH0 |
GPIO5 | Usable | VSPI CS0 |
GPIO6 | Unusable | Internal SPI flash |
GPIO7 | Unusable | Internal SPI flash |
GPIO8 | Unusable | Internal SPI flash |
GPIO9 | Unusable | Internal SPI flash |
GPIO10 | Unusable | Internal SPI flash |
GPIO11 | Unusable | Internal SPI flash |
GPIO12 | Usable | ADC2_CH5TOUCH5HSPI MISOJTAG TDI |
GPIO13 | Usable | ADC2_CH4TOUCH4HSPI MOSIJTAG TCK |
GPIO14 | Usable | ADC2_CH6TOUCH6HSPI SCLKJTAG TMS |
GPIO15 | Usable | ADC2_CH3TOUCH3HSPI CS0JTAG TDO |
GPIO16 | Usable | UART2 RX |
GPIO17 | Usable | UART2 TX |
GPIO18 | Usable | VSPI SCLK |
GPIO19 | Usable | VSPI MISO |
GPIO20 | Unusable | Not exposed |
GPIO21 | Usable | I²C SDA (default) |
GPIO22 | Usable | I²C SCL (default) |
GPIO23 | Usable | VSPI MOSI |
GPIO24 | Unusable | Not exposed |
GPIO25 | Usable | DAC1ADC2_CH8 |
GPIO26 | Usable | DAC2ADC2_CH9 |
GPIO27 | Usable | ADC2_CH7TOUCH7 |
GPIO28 | Unusable | Not exposed |
GPIO29 | Unusable | Not exposed |
GPIO30 | Unusable | Not exposed |
GPIO31 | Unusable | Not exposed |
GPIO32 | Usable | ADC1_CH4TOUCH9 |
GPIO33 | Usable | ADC1_CH5TOUCH8 |
GPIO34 | Input only | ADC1_CH6 · input only |
GPIO35 | Input only | ADC1_CH7 · input only |
GPIO36 | Input only | ADC1_CH0 · input only |
GPIO37 | Unusable | ADC1_CH1 · usually tied to flash |
GPIO38 | Unusable | ADC1_CH2 · usually tied to flash |
GPIO39 | Input only | ADC1_CH3 · input only |
Individual GPIO pages
ESP32 GPIO0Details, cautions and sample codeESP32 GPIO2Details, cautions and sample codeESP32 GPIO12Details, cautions and sample codeESP32 GPIO15Details, cautions and sample codeESP32 GPIO34Details, cautions and sample code
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Peripheral guidesI²C · SPI · UART · RMT · LEDC · deep sleep