1 Basics SPI has three-wire mode and four-wire mode. The three-wire mode consists of three wires - SS (Slave Select), SCK (SPI Clock), and MOSI (Master-In-Slave-Out). The four wire mode has an extra line called MISO (Master-In-Slave-Out). Signals Full Name SS Slave Select SCK SPI Clock MOSI Master-Out-Slave-In MISO Master-In-Slave-Out SPI clock has four modes: CPOL=0/1 and CPHA=0/1. CPOL stands for clock polarity – clock low or high when in idle....