这个指示灯有2个作用，作用1是指示5V总电源，作用2是指示并口电平输出，

若完成学习板的使用后没断开并口线，它会作出半亮指示，若短时间内要经常使用学习板，关闭电源开关即可。

-2 role in this indicator, the role is instructions 5V power supply, the role of instructions parallel level output, after the completion of the learning board did not disconnect the parallel cable, it will make a semi-bright instructions, if a short period of time to be frequently used learning board, turn off the power button.