ESP8266

common pins

pin setup func Note
U0_RXD GPIO3 I/O UART Rx during flash programming  
U0_TXD GPIO1 I/O UART TX during flash programming; SPI_CS1

serial1 =

bootstrap

pin setup func
RESET pull up + cap 0.1 UF  
EN pull up  
IO0 pull up  
IO2 pull up on-module LED
GPIO15 pull down  

Modules

ref

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