Configuration

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This page will tell you more about some things that you may need to know about when using the ESP8266 units (boot states of GPIOs, input voltages, etc. etc). Please beware that this is a generic list, your specific ESP unit might have other restrictions than these general ones. Refer to the ESP Hardware page if you want to be sure what GPIOs that are available and their usefulness.

GPIO on ESP8266

GPIO Number GPIO Name Boot State Precautions and information
0 D3 HIGH for boot
LOW for serial programming
Pullup resistor on most boards
1 Used as serial (TX)
May be used but observe that signal might flicker due to serial activity during boot.
2 D4 HIGH for boot
HIGH for serial programming
Connected to onboard LED (low active)
Used as serial1 (TX1)
3 Used as serial (RX)
May be used but observe that signal might flicker due to serial activity during boot.
4 D2 Generally used as SDA (I2C)
5 D1 Generally used as SCL (I2C)
6 Do not use!
Reserved for SPI + flash
7 Do not use!
Reserved for SPI + flash
8 Do not use!
Reserved for SPI + flash
9 D11 Use with caution!
Reserved for SPI + flash
10 D12 Use with caution!
Reserved for SPI + flash
11 Do not use!
Reserved for SPI + flash
12 D6
13 D7
14 D5
15 D8 LOW for boot Pulldown resistor on most boards
16 D0 No PWM (counter not possible). No internal pullup available. Used in sleep mode for wakeup