esphome-docs/devices/esp8266.rst

Generic ESP8266
===============

.. seo::
    :description: Instructions for using generic ESP8266s with ESPHome.
    :image: esp8266.png
    :keywords: ESP8266

All ESP8266-based devices are supported by ESPHome. Simply select ``ESP8266`` when
the ESPHome wizard asks you for your platform and choose a board type
from `this link <http://docs.platformio.org/en/latest/platforms/espressif8266.html>`__ when the wizard
asks you for the board type.


.. code-block:: yaml

    # Example configuration entry
    esphome:
      name: livingroom
      platform: ESP8266
      board: <BOARD_TYPE>

Many boards have a pin numbering for the exposed pins that is different from the internally used
ones. ESPHome tries to map the silk-screen pin numbers into the internal pin numbers with a few
boards, but for generic ESP8266 boards it is often required to just use the internal pin numbers.
To do this, just prefix all pins with ``GPIO``, for example ``GPIO0`` for the pin with the internal pin
number 0.

Some notes on the pins:

- ``GPIO6`` - ``GPIO11``, ``GPIO0``, ``GPIO2`` and ``GPIO15`` are often already used by the internal
  flash interface and boot mode detection. So it's best to avoid using these pins.
- ``GPIO17`` additionally has an ADC connected to it. See the :doc:`/components/sensor/adc`
  to read voltages (in the range from 0 to 1.0V) on this pin.


.. code-block:: yaml

    # Example configuration entry
    esphome:
      name: livingroom
      platform: ESP8266
      board: nodemcuv2

    binary_sensor:
      - platform: gpio
        name: "Pin GPIO17"
        pin: GPIO17


Special Pins
------------

=================== =============================================
``GPIO0``           Controls Boot Mode
------------------- ---------------------------------------------
``GPIO1``           UART TX pin
------------------- ---------------------------------------------
``GPIO2``           Controls Boot Mode
------------------- ---------------------------------------------
``GPIO3``           UART RX pin
------------------- ---------------------------------------------
``GPIO6``           SDIO/Flash CLK pin
------------------- ---------------------------------------------
``GPIO7``           SDIO/Flash Data 0 pin
------------------- ---------------------------------------------
``GPIO8``           SDIO/Flash Data 1 pin
------------------- ---------------------------------------------
``GPIO9``           SDIO/Flash Data 2 pin (qio/qout only)
------------------- ---------------------------------------------
``GPIO10``          SDIO/Flash Data 3 pin (qio/qout only)
------------------- ---------------------------------------------
``GPIO11``          SDIO/Flash CMD pin
------------------- ---------------------------------------------
``GPIO12``          Attached to Hardware SPI controller MISO
------------------- ---------------------------------------------
``GPIO13``          Attached to Hardware SPI controller MOSI
------------------- ---------------------------------------------
``GPIO14``          Attached to Hardware SPI controller CLK
------------------- ---------------------------------------------
``GPIO15``          Controls Boot Mode; Attached to Hardware SPI
                    controller CS
------------------- ---------------------------------------------
``GPIO16``          Special pin that can be accessed from RTC,
                    and is Deep-Sleep wakeup pin
------------------- ---------------------------------------------
TOUT aka ``GPIO17`` ADC pin for measuring voltages, can only be
                    used as analog input pin
=================== =============================================

This means effectively only the following pins can be used as general purpose GPIO:

========== ============================== ==============================
**Pin**    **Restrictions**               **State after Reset**
---------- ------------------------------ ------------------------------
``GPIO0``  If HIGH on boot                Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO2``  If HIGH on boot                Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO4``                                 High Impedance
---------- ------------------------------ ------------------------------
``GPIO5``                                 High Impedance
---------- ------------------------------ ------------------------------
``GPIO6``                                 Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO12``                                Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO13``                                Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO14``                                Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO15`` If LOW on boot                 Weak Pull Up
---------- ------------------------------ ------------------------------
``GPIO16`` Has pull-down (but no pull-up  Weak Pull Down
           resistor
========== ============================== ==============================

Boot Modes
----------

On each boot, the ESP8266 will check three pins to determine in which boot mode to enter.
There are three boot modes:

========================= ========= ========= ========== ==============
**Mode**                  ``GPIO0`` ``GPIO2`` ``GPIO15`` ``boot mode:``
------------------------- --------- --------- ---------- --------------
Boot from Flash (normal)  HIGH      HIGH      LOW        3
------------------------- --------- --------- ---------- --------------
Download Code from UART   LOW       HIGH      LOW        1
------------------------- --------- --------- ---------- --------------
Boot from SD-Card         ANY       ANY       HIGH       4-7
========================= ========= ========= ========== ==============

You can identify these on boot-up by looking at the UART output, the first number
in the ``boot mode:`` line tells you what mode was selected

.. code-block:: text

    ets Jan  8 2013,rst cause:4, boot mode:(3,6)

The first lines when viewing the UART logs might have unrecognized characters. This is
because the ESP8266 bootloader uses a baudrate of 76800, whereas the program uses 115200.

Reset Causes
------------

Additionally, the first line also contains the **reset cause**.
These reset causes `are documented
<https://www.espressif.com/sites/default/files/documentation/esp8266_reset_causes_and_common_fatal_exception_causes_en.pdf>`__:

== ===================================
0  Undefined
-- -----------------------------------
1  Power On Reboot
-- -----------------------------------
2  External reset or deep-sleep wakeup
-- -----------------------------------
4  Hardware WDT reset
== ===================================

After a software reset, the reset cause will not change.

Electrical Characteristics
--------------------------

=========================================================== =========== =========== =========== ===========
**Parameter**                                               **Min.**    **Typical** **Max.**    **Unit**
----------------------------------------------------------- ----------- ----------- ----------- -----------
Operating Temperature                                       -40                     125         °C
----------------------------------------------------------- ----------- ----------- ----------- -----------
Working Voltage ``V_IO``                                    2.5         3.3         3.6         V
----------------------------------------------------------- ----------- ----------- ----------- -----------
``V_IL`` - INPUT voltage level to be considered LOW         -0.3                    0.25*V_IO   V
----------------------------------------------------------- ----------- ----------- ----------- -----------
``V_IH`` - INPUT voltage level to be considered HIGH        0.75*V_IO               3.6         V
----------------------------------------------------------- ----------- ----------- ----------- -----------
``V_OL`` - OUTPUT voltage level for LOW                                             0.1*V_IO    V
----------------------------------------------------------- ----------- ----------- ----------- -----------
``V_OH`` - OUTPUT voltage level for HIGH                    0.8*V_IO                            V
----------------------------------------------------------- ----------- ----------- ----------- -----------
``I_MAX`` - Maximum current for GPIO                                                12          mA
----------------------------------------------------------- ----------- ----------- ----------- -----------
Power Consumption in Deep Sleep                                         20                      µA
----------------------------------------------------------- ----------- ----------- ----------- -----------
Power Consumption in Active Mode                                        120                     mA
=========================================================== =========== =========== =========== ===========

Source: `ESP8266EX datasheet <https://www.espressif.com/sites/default/files/documentation/0a-esp8266ex_datasheet_en.pdf>`__

The internal pull up/down resistors have values of 30kΩ to 100kΩ
(`source <https://bbs.espressif.com/viewtopic.php?t=1079>`__).

See Also
--------

- :doc:`nodemcu_esp8266`
- :ghedit:`Edit`