说明：  89S52 单片机的P1 口接有 8个 LED，当某一端口输出为“0”时， 相应的 LED 点亮，P3.2、P3.3、P3.4、P3.5 分别接有四个按钮 K1~K4，按下按钮时，相应 引脚被接地。现要求编写可键控的流水灯程序，当 K1 按下时，开始流动，K2 按下时停止 流动，全部灯灭，K3 使灯由上往下流动，K4 使灯由下往上流动。
(P1 port access 89S52 microcontroller with 8 LED, when the port outputs a " 0" , the corresponding LED light, P3.2, P3.3, P3.4, P3.5 respectively, then there are four buttons K1 ~ K4, press the button, the corresponding pin is grounded. Are prepared in water can be keyed light procedure, when K1 pressed, starts to flow, K2 is pressed to stop the flow, all lights are out, K3 mobile to light from top to bottom, K4 so that light flows from bottom to top.)