General-purpose I/O is a topic near to the hearts of Raspberry Pi owners because this is the interface to the outside world. The Pi is flexibly designed to allow I/O pins to be reconfigured under software control. For example, GPIO 14 can be an input, an output, or operate as a serial port TX data line.
One of the challenges related to the Pi’s GPIO interface is that it uses a weak CMOS 3.3 V interface. The GPIO pins are also susceptible to ESD (electrostatic discharge) damage and are weak drivers (2 to 16 mA). Finally, the limited GPIO power must be budgeted from the total spare current capacity ...
