The Serial Peripheral Interface (SPI) is a synchronous serial communication protocol that is widely used for short-distance communication, primarily between microcontrollers and peripheral integrated circuits on the same printed circuit board (PCB). It was developed by Motorola and has become a de facto standard.
SPI uses a master-slave architecture and typically requires four signal lines:
SCLK (Serial Clock): The clock signal, generated by the master, that synchronizes the data transfer.
MOSI (Master Out, Slave In): The data line used for sending data from the master to the slave. (Also called SIMO).
MISO (Master In, Slave Out): The data line used for sending data from the slave back to the master. (Also called SOMI).
SS (Slave Select) or CS (Chip Select): A signal used by the master to select which slave device it wants to communicate with.
Because it uses separate lines for sending and receiving data, SPI can operate in a full-duplex mode, meaning data can be sent and received simultaneously.
It is generally simpler and capable of higher speeds than I2C, but it requires more pins on the microcontroller. SPI is commonly used to interface with components like flash memory chips, ADCs, DACs, and display drivers within an electronic device like a programmable power supply. While the end-user controls the power supply via USB or LAN, the internal microcontroller may be using SPI to communicate with its own core components.