如图4.3.1所示，AT89S51单片机的P1.0－P1.3接四个发光二极管L1－L4，P1.4－P1.7接了四个开关K1－K4，编程将开关的状态反映到发光二极管上。（开关闭合，对应的灯亮，开关断开，对应的灯灭）。 -As shown in Figure 4.3.1, AT89S51 MCU P1.0-P1.3 take four light emitting diodes L1-L4, P1.4-P1.7 received four switches K1-K4, programming reflected the state of the switch light-emitting diode. (Switch is closed, the corresponding lights, switch off the corresponding lamp).