 <ul>
       <li>GPIO15 is always pulled low, so you can’t use the internal pull-up resistor. You have to keep this in mind when using GPIO15 as an input to read a switch or connect it to a device with an open-collector (or open-drain) output, like I²C.</li>
       <li>GPIO0 is pulled high during normal operation, so you can’t use it as a Hi-Z input.</li>
       <li>GPIO2 can’t be low at boot, so you can’t connect a switch to it.</li>
   </ul>
   <h4>Internal pull-up/-down resistors</h4>
   <p>GPIO