Serial Peripheral Interface Bus

The Serial Peripheral Interface bus (SPI) is a synchronous serial communication interface specification used for short distance communication, primarily in embedded systems. The interface was developed by Motorola in the late eighties and has become a de facto standard. Typical applications include Secure Digital cards and liquid crystal displays.

SPI devices communicate in full duplex mode using a master-slave architecture with a single master. The master device originates the frame for reading and writing. Multiple slave devices are supported through selection with individual slave select (SS) lines.

Sometimes SPI is called a four-wire serial bus, contrasting with three-, two-, and one-wire serial buses. The SPI may be accurately described as a synchronous serial interface, but it is different to the Synchronous Serial Interface (SSI) protocol, which is also a four-wire synchronous serial communication protocol, but employs differential signaling and provides only a single simplex communication channel.

The SPI bus specifies four logic signals:

Alternative naming conventions are also widely used, and SPI port pin names for particular IC products may differ from those depicted in these illustrations:

Serial Clock:

Master Output ${\displaystyle \rightarrow }$ Slave Input:

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