这个程序主要是讲解SPI总线。SPI(Serial Peripheral Interface--串行外设接口)总线系统是一种同步串行外设接口，它可以使MCU与各种外围设备以串行方式进行通信以交换信息。该接口一般使用4条线：串行时钟线（SCLK）、主机输入/从机输出数据线MISO、主机输出/从机输入数据线MOSI和低电平有效的从机选择线NSS(有的SPI接口芯片带有中断信号线INT、有的SPI接口芯片没有主机输出/从机输入数据线MOSI)。很多的芯片使用SPI进行通信，比如语音芯片等。掌握了基本的SPI总线的操作，对于操作那些芯片是非常简单的。-This program is mainly to explain the SPI bus. SPI (Serial Peripheral Interface- Serial Peripheral Interface) bus system is a synchronous serial peripheral interface, which allows MCU with a variety of peripheral devices in a serial manner to communicate to exchange information. The interface is generally used four lines: a serial clock line (SCLK), master input/slave output data lines MISO, master output/slave input data lines MOSI and active-low slave select lines NSS (some SPI interface chip with interrupt signal line INT, and some do not host SPI interface chip output/slave input data lines MOSI). Many chips use SPI communication, such as voice chips. Mastered the basic operations SPI bus operation for those chips is very simple.