SPI bus system is a synchronous ser

SPI bus system is a synchronous serial peripheral interface. It allows the CPU to communicate with a variety of peripheral interface devices in a serial manner, exchange information. Peripheral interface devices include TTL shift register (used as parallel input or output), A/D or D/A converter, real-time clock (RTO), memory, LCD and LED display drivers, etc. The SPI system uses four lines: serial clock (SCK), MASTER Input/slave output data line (MISO), Master Output/slave input data line (MOSI), and low level effective slave gate line. SPI system bus only needs 3 ~ 4 data lines and control lines to extend various I/O devices with SPI interface, while parallel bus extension method needs 8 data lines, 8 ~ 16 bit address lines and 2 ~ 3 bit control lines, so the use of SPI bus can simplify circuit design and improve the reliability of design