SPI is quite straightforward – it defines features any digital electronic engineer would think of if
it were to quickly define a way to communicate between 2 digital devices. SPI is a protocol on 4
signal lines (please refer to figure 1):
- 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).