ESP-12F pinouts reference : How to use it in our designs
ESP-12F Pin Overview The ESP-12F module, based on the ESP8266EX, breaks out 22 pins. However, only 17 GPIO-related pins are practically usable, and several of them have important restrictions. Title in Other Languages German: ESP-12F Pinout-Referenz: Wie man es in eigenen Designs verwendet French: Référence du brochage de l’ESP-12F : Comment l’utiliser dans vos conceptions Spanish: Referencia de pines del ESP-12F: Cómo usarlo en tus diseños Italian: Guida ai pin di ESP-12F: Come usarlo nei tuoi progetti Portuguese (Brazil): Referência de pinagem do ESP-12F: Como usar em seus projetos Tip: Right-click anywhere on this page and choose “Translate to your language”. Complete Pin Reference Table Pin Label GPIO Type Boot/Strapping Function Notes ADC ADC0 Analog Input — 0–1.0V range only, no GPIO function EN (CH_PD) — Enable Must be HIGH to run Pull-up required (10kΩ) RST — Reset Active LOW Pull-up internally, can leave floating GPIO16 (XPD_DCDC) 16 I/O No pull-up/down, no interrupt support Used for deep-sleep wake-up (connect to RST) GPIO14 14 I/O HSCLK General purpose GPIO12 12 I/O HMISO General purpose GPIO13 13 I/O HMOSI General purpose GPIO15 15 I/O Strapping pin – must be LOW at boot HSPICS, has internal pull-down GPIO2 2 I/O Strapping pin – must be HIGH at boot UART1 TXD, internal pull-up GPIO0 0 I/O Strapping pin – boot mode select HIGH = normal boot, LOW = flash/programming mode GPIO4 4 I/O — Recommended for I2C SDA GPIO5 5 I/O — Recommended for I2C SCL GPIO9 (SD2) 9 I/O Used by SPI flash (in some modes) Avoid unless not using QIO flash mode GPIO10 (SD3) 10 I/O Used by SPI flash (in some modes) Avoid unless not using QIO flash mode RXD (GPIO3) 3 Input mostly UART0 RX Can be used as input-only GPIO if UART is not needed TXD (GPIO1) 1 I/O Strapping pin – must be HIGH at boot UART0 TX, affected by boot messages VCC — Power 3.3V only Not 5V tolerant GND — Ground — Multiple GND pins for thermal and RF performance Critical Design Considerations 1. Strapping Pins (Boot Mode Selection) These pins are sampled at reset/boot and determine boot behavior: Pin Must Be at Boot If Violated GPIO0 HIGH = run mode, LOW = flash mode Wrong boot mode GPIO2 HIGH Boot failure if pulled LOW GPIO15 LOW Boot failure if pulled HIGH or left floating Design rule: Avoid connecting these pins to devices that force them LOW or HIGH during power-up, such as LEDs, buttons, or external peripherals without proper pull resistors. 2. Input-Only / Restricted Pins GPIO3 (U0RXD): Mostly input-only when not used for UART0. This is the default UART0 receive pin for programming and debugging. If UART0 is inactive or remapped, GPIO3 can serve as a general input, but it is not a good choice for general output use. GPIO16: No pull-up/pull-down resistor, no interrupt support, and not suitable for PWM or I2C. It is mainly used for deep-sleep wake-up by connecting it to RST. ADC0: Analog input only, not a GPIO pin. Maximum input voltage is 1.0V. It is a 10-bit ADC, so the reading range is 0 to 1024. 3. Pins to Avoid for General GPIO Use GPIO6–GPIO11: Internally connected to the SPI flash memory. Do not use them unless you fully understand your flash mode configuration. GPIO9 and GPIO10: Especially risky in QIO flash mode and generally best avoided. GPIO1 (TX) and GPIO3 (RX): Usable as GPIO only if you do not need serial communication or debug output. 4. Power Considerations Requires a stable 3.3V supply. Peak current can reach approximately 300mA during Wi-Fi transmit bursts. Add decoupling capacitors close to the VCC pin, typically 100µF + 100nF. EN (CH_PD) must have a pull-up resistor, typically 10kΩ. If EN floats, the module may not boot. 5. Reset Behavior RST is active LOW. Add a pull-up resistor and, if needed, a small capacitor to GND for better noise immunity. Automatic reset circuits for auto-flashing often use RTS and DTR from a USB-to-serial converter through transistors or diodes. SPI and HSPI on ESP-12F The ESP8266 has two SPI controllers: SPI: Usually reserved for internal flash memory. According to datasheet these pin are internally connected to SPI flash chip and they are not available from outside. HSPI: Available for user applications such as displays, sensors, and SD cards ESP-12F HSPI Pin Mapping HSPI Function ESP8266 GPIO ESP-12F Physical Pin Name Description HSPI_MISO (Master In Slave Out) GPIO12 MISO / IO12 Data input to the ESP8266 HSPI_MOSI (Master Out Slave In) GPIO13 MOSI / IO13 Data output from the ESP8266 HSPI_CLK (Serial Clock) GPIO14 SCLK / IO14 Clock signal HSPI_CS (Chip Select) GPIO15 CS / IO15 / TXD2 Slave select / chip select Important Hardware Considerations for HSPI GPIO15 (HSPI_CS) Boot Strap Pin:GPIO15 is a boot strapping pin. For the ESP8266 to boot successfully from SPI flash, GPIO15 must be pulled LOW during boot, usually with a 10kΩ pull-down resistor. Design tip: If you connect a peripheral’s chip select pin to GPIO15, make sure the peripheral does not pull the line HIGH during startup, or the ESP-12F may fail to boot. GPIO12 (HSPI_MISO) Consideration:Depending on the flash configuration, GPIO12 can sometimes affect startup behavior if it is forced HIGH during boot. In most designs, it is safest to leave it floating or ensure it is not strongly driven during reset. Is I2C on the ESP8266/ESP-12F Hardware or Software? On the ESP8266, I2C is implemented as a software (bit-banged) peripheral. Unlike the ESP32, which has dedicated hardware I2C controllers, the ESP8266 does not expose a true hardware I2C peripheral on its standard GPIOs. Instead, the SDK and environments such as MicroPython typically implement I2C in software. Because it is software-based: You can use almost any two GPIO pins for SDA and SCL. It uses more CPU time than hardware I2C, but for most sensors, EEPROMs, and small displays, it works very well. Recommended I2C Pins For most tutorials and practical projects, the cleanest default choice is: Signal ESP8266 GPIO ESP-12F Pin Label NodeMCU Label Recommendation