本例子是用硬件SPI接口循环发送一个变量到74HC595，并且在数据发送完毕后通过单片机的另外一个IO接口PB2输出一个“锁存”脉冲 ，使74HC595把移位寄存器的数据输出到锁存寄存器,并驱动8个LED输出，实现来回流水的效果。-This example is using the hardware SPI interface to send a variable to the loop 74HC595, and after the data is sent through the microcontroller interface to another IO PB2 output a " latch"　pulse, the 74HC595 shift register to latch the data output to the register, and drive 8 LED outputs, to achieve the effect of water back and forth.