说明：  BCD\七段显示译码器 数码管段显示发光二级管是共阴连结，所以显示高电平有效，即哪一段的驱动信号为高电平，则对应段发亮
(BCD \ seven-segment display decoder digital tube sections show light-emitting diode is a link to a total of yin, it showed high and effective, that is what section of the drive signal is high, then the corresponding segment bright)