SPI

The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in a master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select (chip select) lines using a pin for each device. There is a wide availability of sensors that communicate using SPI as protocol. Check the examples included with the library.

Including this library automatically defines constants for the pins involved: SS, SCK, MOSI, MISO, making it possible to use them in regular commands like: digitalWrite(SS, HIGH); For the physical location of these pins check the hardware reference. On Wiring v1 boards the SPI pins are: SS=24, MOSI=25, MISO=26 and SCK=27. On Wiring S board the SPI pins are: SS=20, MOSI=21, MISO=22 and SCK=23.