emory chip. This is the small 8-legged chip right next to the ESP8266. If you try to use one of these pins, you might crash your program.</p>
   <p>GPIO 1 and 3 are used as TX and RX of the hardware Serial port (UART), so in most cases, you can’t use them as normal I/O while sending/receiving serial data.</p>
   <h4>Boot modes</h4>
   <p>As mentioned in the previous chapter, some I/O pins have a special function during boot: They select 1 of 3 boot modes:</p>
   <table style="box-sizing: border-box; borde