# ESP8266

* [Reference](https://randomnerdtutorials.com/esp8266-pinout-reference-gpios/)
* ![](.\esp8266-pinout.JPG)
* Best Pins to Use

Label | GPIO | Input | Output | Notes
---|----|----|----|----|----
D0 | GPIO16 | no interrupt | no PWM or I2C support | HIGH at boot used to wake up from deep sleep
D1 | GPIO5 | OK | OK | often used as SCL (I2C)
D2 | GPIO4 | OK | OK | often used as SDA (I2C)
D3 | GPIO0 | pulled up | OK | connected to FLASH button, boot fails if pulled LOW
D4 | GPIO2 | pulled up | OK | HIGH at boot connected to on-board LED, boot fails if pulled LOW
D5 | GPIO14 | OK | OK | SPI (SCLK)
D6 | GPIO12 | OK | OK | SPI (MISO)
D7 | GPIO13 | OK | OK | SPI (MOSI)
D8 | GPIO15 | pulled to GND | OK | SPI (CS) Boot fails if pulled HIGH
RX | GPIO3 | OK | RX pin | HIGH at boot
TX | GPIO1 | TX pin | OK | HIGH at boot debug output at boot, boot fails if pulled LOW
A0 | ADC0 | Analog Input | X