Also known as: SPI
SPI (Serial Peripheral Interface) is a fast, full-duplex serial bus that connects a controller to one or more peripheral chips.1
Overview
SPI uses four lines: a clock (SCLK), data out (MOSI), data in (MISO), and a chip-select (CS) per peripheral. Because data flows both directions on every clock edge, it is full-duplex and can run at tens of MHz — much faster than I²C. The cost is wiring: each additional peripheral needs its own chip-select line rather than an address. A microcontroller’s SPI peripheral shifts the bits in hardware.
Where it fits
SPI is the bus of choice when speed matters: driving displays, reading high-rate ADCs, and talking to flash memory and SD cards. Many sensors offer SPI as a faster alternative to I²C. It is also the interface behind AVR-style in-system programming. Choosing between SPI, I²C, and UART is a routine design decision in any embedded system.
Sources
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Serial Peripheral Interface — Wikipedia, on the SPI bus and its lines. ↩