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Moderator: igrr

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By QuickFix
#91060 Not all GPIO's of the ESP are created equal: some can have any (high or low) state at boot, others can't.
The ESP will not boot if GPIO15 is pulled high (scroll down to "Best Pins to Use" and "Pins used during Boot"). :idea:

The ESP8266 is not an ATMEL µC; the great thing we can use Arduino code, doesn't mean everything is 1:1 similar or compatible.