The serial lateral communication bus (SPI) is a synchronized serial data link named by Motorola that operates in fully two-way Mode. This type of communication is used in short distances with only one "Overlord" such as latent systems، sensors and SD cards.In this type of communication devices communicate in the form of Master / Slave, which in en the master device sets up data frames. It is also possible to communicate with several slaves with selection lines separate from a common line. Sometimes for separation SPI of 3-wire serial crossings two wires and one wire also called 4-wire serial crossings.