SPI and I2C are common communication protocols used to connect devices in embedded systems. SPI uses a master-slave configuration with four lines for synchronous full-duplex communication between a master and slave devices. I2C also uses a master-slave configuration and supports multiple slave devices on the same bus, each with a unique address selected by the master for communication. While SPI supports higher data transfer speeds, I2C is commonly used for sensors and other low to moderate bandwidth devices that need to share a bus. The choice between SPI and I2C depends on the specific application needs and factors like speed and number of devices.