SPI or Serial Peripheral Interface Bus is a synchronous four-wire serial communication interface. Devices communicate in full duplex mode using a master-slave architecture with a single master connected to multiple slaves. Slaves are selected using multiple slave select (SS) lines.

Four signals are used:

  • SCLK: Serial Clock (output from master).
  • MOSI: Master Output Slave Input, or Master Out Slave In (data output from master).
  • MISO: Master Input Slave Output, or Master In Slave Out (data output from slave).
  • SS: Slave Select (often active low, output from master).
See also