2.用四个按键和一个数码管制成简易的密码锁。四个按键分别代表数字0、1、2、3，密码设定为3，开机数码管显示“-”，等待密码输入，输入正确时，显示字符“3”2秒，打开门，输入错误时，显示“F”2秒，按要求完成下列题目。-2 with four buttons and a digital control into a simple lock. Four buttons representing the numbers 0, 1, 2, 3, and the password is set to 3, boot digital display " -"　wait for password entry when you enter the correct character " 3"　2 seconds, opened the door, enter the error , show " F"　2 seconds required to complete the following topics.