系统上电复位后，系统就处于等待状态，当K0到K7有按键动作时，单片机会将动作的按键号0到7串行发送到串并转换芯片74LS164中，芯片74LS164使74LS240驱动数码管显示按键所对应的按键号。-System power-on reset, the system in a wait state, when there are key K0 to K7 action, single-chip will be the key actions 0-7 serial number is sent to the SERDES 74LS164 chip, the 74LS240 driver chips 74LS164 make digital tube shows the corresponding button number keys.