1.1 Serial Communication

To begin a serial communication in the SPI protocol, the master must send out the first clock signal (SCK) to the slave at a frequency that both devices support. The master device always controls the SPI timing and provides the clock signal to all of the slave devices on the bus. Slave devices are not capable of manipulating the SPI clock in any way. No data can be transferred unless a clock signal is present. The slave devices on the SPI bus will always receive the SPI clock signal, but will not respond to the SPI master until their respective Slave Select line has been activated. Once a slave device has been initiated by the SPI master, the slave can respond and data can be transferred one bit at a time, sequentially over the SPI bus.