SPI Overview & History

SPI (Serial Peripheral Interface) is a synchronous serial communication protocol invented by Motorola in the 1980s. It is widely used for high-speed communication with peripherals like ADCs, DACs, displays, and flash memory.

• Bus Lines: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCLK (Clock), CS (Chip Select)
• Speed: Typically several MHz, limited by physical layer
• Topology: Single master, multiple slaves using separate CS lines
• Full Duplex: Yes, data can flow both directions simultaneously

SPI Technical Function

SPI transfers data using **shift registers** in master and slave devices:

1. Master sets CS low to select a slave.
2. Master generates SCLK and shifts out data on MOSI.
3. Slave shifts data out on MISO simultaneously (full duplex).
4. Data is latched on the rising/falling edge of SCLK depending on mode (CPOL/CPHA).
5. Master sets CS high to end the transaction.

SPI Diagram