ESP8266 Especificações

This table 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.

From: https://www.letscontrolit.com/wiki/index.php?title=Configuration