Embeded - ESP8266 Boot Config GPIO and Onboard LED 

Page / - last modified by Victor Zhang on 13:12, 17/04/2020 

ESP8266 Boot Config GPIO and Onboard LED 
last modified by Victor Zhang
on 13:12, 17/04/2020

Table of Contents

•	Ref: http://www.forward.com.au/pfod/ESP8266/GPIOpins/index.html
•	Summary:
•	GPIO0/GPIO2/GPIO15 pins are used to determine in which mode ESP8266 will boot, so avoid using them as persistant pulling Input source.
•	A button with normally open to Ground with internal pullup is OK
•	A button with normally closed to VDD/GND is likely NOT OK (Only OK when it fits the mode for booting, however will possibly make reprogramming impossible)
•	Sensor module which will have a High/Low to the chip is NOT OK (sometime will make it try to go into program mode)
•	In the generic NodeMCU, the PIN identifiers are: D3,D4 and D8
•	Use them as output is the best practise
•	GPIO2/GPIO16 also connected with Drain mode LED( Low level light up), identifiers are D4 and D0
•	Ref: https://lowvoltage.github.io/2017/07/09/Onboard-LEDs-NodeMCU-Got-Two