SPI - Serial Peripheral Interface

SPI0 pins in BCM mode are: 9, 10, 11 + 7/8

SPI0 pins in WiringPi are: 12, 13, 14 + 10/11

Known as the four-wire serial bus, SPI lets you daisy-chain multiple compatible devices off a single set of pins by assigning them different chip-select pins.

A useful example of an SPI peripheral is the MCP23S17 digital IO expander chip ( Note the S in place of the 0 found on the I2C version ). You can also use the SPI port to "Bit-Bang" an ATmega 328, loading Arduino sketches onto it with Gordon Hendersons' modified version of AVRDude.

To talk to an SPI device, you assert its corresponding chip-select pin. By default the Pi has CE0 and CE1.

import spidev
spi = spidev.SpiDev()
spi.open(0, CHIP_SELECT_0_OR_1)
spi.max_speed_hz = 1000000
spi.xfer([value_8bit])