用74HC595驱动两个数码管，属于静态显示,

74HC595是一个三态输出8位移位/锁存器,

SCK是时钟输入引脚，接PD6

在SCK的上升沿SER的上的电平信号被读入内部寄存器最底位接PD4

RCK是锁存控制脚，在上升沿内部寄存器的内容被锁存到相应输出脚的锁存器中，接PD5-74HC595 driven by two digital tube, is a static display, 74HC595 is a three-state output 8-bit shift/latch, SCK is the clock input pin, and then in the PD6 the rising edge of SCK on the SER-level signals are read into the most at the end of the internal register access PD4 RCK-bit latch control pin is in the rising edge of the contents of internal registers to be latched to the corresponding output pin of the latch, and then PD5