Pulse width modulation

The universal asynchronous receiver/transmitter (UART) modules are used to transmit and receive RS-232 style serial signals, which is an industry standard for serializing and transferring information between two devices using a pair of unidirectional digital signals. They can be used to communicate with PCs, Bluetooth and Wi-Fi radio modules, and GPS receivers. The BeagleBone Black's UART modules also operate at 3.3V.

The serial peripheral interface (SPI) module is used to communicate over SPI, which is another industry standard serial protocol. Whereas UARTs are generally used to connect two devices, SPI is made to connect one master device to one or many slave devices. It is commonly used on devices such as small character and graphics LCD screens, external ADCs, and DACs (Digital-to-Analog converters), as well as on many different types of sensor. The BeagleBone Black's SPI modules operate at 3.3V as well.

Inter-Integrated Circuit (I2C) is yet another industry standard serial protocol. It also allows a master device to communicate with a bus of many slave devices, but it requires fewer pins than SPI. It is commonly used by real-time clocks (RTCs), as well as in many types of sensors, including Micro-Electro-Mechanical Systems (MEMS) devices, such as accelerometers, magnetometers, and gyroscopes. The BeagleBone's I2C modules operate at 3.3V.