- A clock signal named SCLK, sent from the bus master to all slaves; all the SPI signals are synchronous to this clock signal;
- A slave select signal for each slave, SSn, used to select the slave the master communicates with;
- A data line from the master to the slaves, named MOSI (Master Out-Slave In) - A data line from the slaves to the master, named MISO (Master In-Slave Out).