SPI

Serial Peripheral Interface Bus (SPI bus) Connects circuitry with few wires over serial protocol.

SPI supports an unlimited number of peripherals, which may all be identical.

Daisy-chained SPI connects all the devices on a SPI bus in a loop. In a daisy-chain SPI loop, the serial data out pin (SDO) of each device connected to the serial data in pin (SDI) of the next device in the loop. A daisy-chained SPI bus uses 4 GPIO pins on the microcontroller, no matter how many SPI peripherals are attached.

Chip-select SPI uses an additional dedicated chip-select pin for each SPI peripheral.

(Other protocols, such as I2C, require each peripheral on the bus to have a different (unique) address).

Further reading

Serial Peripheral Interface Bus

• a redefinition of SPI signal names: "A REDEFINTION OF SPI SIGNAL NAMES" by Nathan Seidle, founder of SparkFun Electronics.