techshopdude @ instructables.com writes:
There are many electronic devices that use the SPI bus, or Serial Peripheral Interface bus, for communications (e.g. various sensors, LCD displays, digital potentiometers, D/A and A/D converters, wireless transmitters and receivers, audio volume controls). The devices receive data serially from a microcontroller using a 3-wire set-up that includes a chip select signal (usually titled CS – when this signal is at logic 0, a chip recognizes it will be receiving or sending data), a clock signal for clocking the serial data into the device, and the serial data stream itself.
Using an Arduino to Control or Test an SPI electronic device - [Link]