说明：  STM8单片机的SPI主从通信，一个STM8单片机当主机，另一个STM8单片机当从机，基本实现了SPI的所有功能，特别适合对SPI的深入理解。
(STM8 microcontroller SPI master or slave communication, a STM8 microcontroller as host another STM8 microcontroller from the machine, the basic realization of all the features of the SPI, especially for in-depth understanding of the SPI.)