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 BCM2835 is flexibly designed to allow I/O pins to be reconfigured under software control. GPIO 14 can be an input, an output, or operate as a serial port TX data line, for example. This makes the Raspberry Pi very adaptable.
One of the challenges related to the Pi’s GPIO interface is that it uses a weak CMOS 3 V interface. The GPIO pins are susceptible to static electricity damage, and the I/O pins are weak drivers (2 to 16 mA). Additionally, GPIO power must be budgeted from the total spare current ...