what is spi?

SPI (Serial Peripheral Interface)

The Serial Peripheral Interface or SPI bus is a synchronous serial data link, a de facto standard, named byMotorola, that operates in full duplex mode. It is used for short distance, single master communication, for example in embedded systems, sensors, and SD cards.Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select lines. Sometimes SPI is called a four-wire serial bus, contrasting with three-,two-, and one-wire serial buses. SPI is often referred to as SSI (Synchronous Serial Interface).

The SPI bus specifies four logic signals:

• SCLK : Serial Clock (output from master).
• MOSI : Master Output, Slave Input (output from master).
• MISO : Master Input, Slave Output (output from slave).
• SS : Slave Select (active low, output from master).

clock, polarity and phase in spi ? At CPOL=0 the base value of the clock is zero For CPHA=0, data are captured on the clock's rising edge (low→high transition) and data is propagated on a falling edge (high→low clock transition). For CPHA=1, data are captured on the clock's falling edge and data is propagated on a rising edge. At CPOL=1 the base value of the clock is one (inversion of CPOL=0) For CPHA=0, data are captured on clock's falling edge and data is propagated on a rising edge. For CPHA=1, data are captured on clock's rising edge and data is propagated on a falling edge. -------------------------------------------------------------------------------------------------------------------------------------------- Common serial interface on many microcontrollers Simple 8-bit exchange between two devices Master initiates transfer and generates clock signal  Slave device selected by master  One-byte at a time transfer Data protocols are defined by application Must be in agreement across devices --------------------------------------------------------------------------------------------------------------------------------------------