The Serial Peripheral Interface(SPI) is a serial bus designed for master- slave operation between Motorola microprocessors and components. The synchronous SPI bus is similar to Philips' I2C bus and National Semiconductor's Microwire, but it is faster than the I2C bus, and is particularly suitable for irregular access applications, such as communication between microprocessors and signal processingchips.
The SPI bus is a serial, synchronous bus consisting of four lines: three control lines for synchronous communication between master and slave and one selection line for the slave. The two signal lines transmit the signals "Master Output, Slave Input" (MOSI) and "Master Input, Slave Output"( MISO), besides there is the line for the clock signal of the slaves (SCLK) and the selection line Slave Select( SS). The SPI bus transmits full duplex and provides different data rates up to 20 Mbps. The SPI protocol is used in smartmeter communication and telemonitoring in telemedicine.
The clock signal is generated in the master and sent to all slaves. The clock frequency can be several megahertz. The output signal of the master is fed to the slave via the MOSI line and the output signal of the slaves is fed back to the master via the MISO line. The SS line is used to activate the corresponding slave. If several slaves are connected to the master, then these can be cascaded or connected to the master via individual SS lines.