如图4.2.1所示，监视开关K1（接在P3.0端口上），用发光二极管L1（接在单片机P1.0端口上）显示开关状态，如果开关合上，L1亮，开关打开，L1熄灭。-As shown in Figure 4.2.1, monitor switch K1 (connected to the P3.0 port), with a light-emitting diode L1 (P1.0 port connected to the MCU) shows off state, if the switch is closed, L1 light, switch open, L1 out.