74165的输入口接8个按键，74164的输出接8个发光二极管，按键按下时，在发光二极管上以十六进制格式显示按键键码。-74165 8 pick the input of key, then the output of 74,164 8 light-emitting diode, button pressed, the LED on the key in hexadecimal format key code.