SPI (Serial Peripheral Interface)

Best for: High-speed, short-distance data transfer on a single circuit board.

How it works: Uses four wires: Master Out Slave In (MOSI), Master In Slave Out (MISO), Serial Clock (SCLK), and Slave Select (SS). It is a full-duplex, synchronous protocol that uses separate wires for data lines instead of addressing, requiring a dedicated SS line for every slave device.

Speed: Very fast, often 10 Mbps to 50+ Mbps.

Distance: Very short, typically a few centimeters on a PCB.