# Peripheral I/O

> Peripheral I/O allows to communicate with sensors and actuators using industry standard protocols and interfaces.

* General Purpose Input/Output (GPIO)
* Pulse Width Modulation (PWM)
* Serial Communication
  * I2C
  * SPI
  * UART

Links

* [Raspberry Pi Pinout](https://pinout.xyz/)
* [Android Things Raspberry Pi I/O](https://developer.android.com/things/hardware/raspberrypi-io.html)

## Pin Muxing

> Many modern microcontroller have a cool feature: Pin Muxing. What it means is that I can ‘mux’ the pins for different purposes: such as I can use a SPI or I2C pin as GPIO (General Purpose Pin) or vice versa. In an ideal world, I would be able to ‘route’ or ‘mux’ pins freely around. In practice these ‘way switches’ are more or less limited. [Reference](https://mcuoneclipse.com/2014/04/18/pin-muxing-using-the-nmi-pin-as-gpio-pin/)


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