SPI is a single-master communication protocol. This means that one central device initiates all
the communications with the slaves. When the SPI master wishes to send data to a slave and/or
request information from it, it selects slave by pulling the corresponding SS line low and it
activates the clock signal at a clock frequency usable by the master and the slave. The master
generates information onto MOSI line while it samples the MISO line (refer to figure 2).