This pin is on the rear of the ESP8266 module, and on many development boards, it isn’t even connected. That’s because its internally hooked up to the ESP8266’s SPI flash chip, and using it ...

The ESP8266 is a chip that turned a lot of heads recently, stuffing a WiFi radio, TCP/IP stack, and all the required bits to get a microcontroller on the Internet into a tiny, $5 module.