The I2C bus interface is used for low-speed devices only. If you want to communicate with faster devices like LCD/LED display units, SD cards, Ethernet modules, then you need to use a faster bus on BeagleBone called the Serial Peripheral Interface (SPI). It provides high data rates in MB/s. Many sensors, DAC, Wi-Fi boards, and microcontroller boards support the SPI protocol. This protocol was developed by Motorola. It is popular in embedded systems.
SPI is a synchronous serial 4-wire protocol. Multiple devices can be connected to a single bus. So, it is a master-slave bus. One line is used to synchronize the clock signal (SCK/SCLK/CLK). The master provides the clock signal to all slaves. Two lines of MOSI and MISO are used to exchange data. MOSI carries data from the master to slave. MISO carries data from the slave to the master. So, SPI is a full duplex communication. MOSI and MISO lines are shared among all slave devices. One line is Chip Select (CS). It is also called Chip...
