用8051单片机编程实现以下功能（1）系统上电后，按下按键，数码管可显示按键对应的字符，如按下“0”键，数码管 显示字符0，按下“F”键，数码管显示 F。 （2）模拟密码锁，设计程序。假设密码为“12AB”，输入 4 位密码后，若输入正确，则 数码管显示“P”；若输入错误，则数码管显示“E”，表示密码错误。在系统不断电情况下， 密码锁在上次开锁或者输入密码错误之后，能继续工作。

以下是8051单片机的程序代码实现：

（1）按键对应字符显示程序

#include<reg52.h>

#define uchar unsigned char
#define uint unsigned int

uchar code table[] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F, 0x77, 0x7C, 0x39, 0x5E, 0x79, 0x71};

void delay(uint xms){
    uint i, j;
    for(i = xms; i > 0; i--)
        for(j = 110; j > 0; j--);
}

void main(){
    uchar key_value;
    P1 = 0x00;  // 数码管段选
    P2 = 0xFF;  // 按键检测
    while(1){
        if(P2 != 0xFF){
            delay(10);  // 消抖
            if(P2 != 0xFF){
                switch(P2){
                    case 0xFE: key_value = 0; break;
                    case 0xFD: key_value = 1; break;
                    case 0xFB: key_value = 2; break;
                    case 0xF7: key_value = 3; break;
                    case 0xEF: key_value = 4; break;
                    case 0xDF: key_value = 5; break;
                    case 0xBF: key_value = 6; break;
                    case 0x7F: key_value = 7; break;
                    case 0xFE: key_value = 8; break;
                    case 0xFD: key_value = 9; break;
                    case 0xFB: key_value = 10; break;
                    case 0xF7: key_value = 11; break;
                    case 0xEF: key_value = 12; break;
                    case 0xDF: key_value = 13; break;
                    case 0xBF: key_value = 14; break;
                    case 0x7F: key_value = 15; break;
                    default: key_value = 0xFF; break;
                }
                P1 = table[key_value];  // 显示对应字符
            }
        }
    }
}

（2）密码锁程序

#include<reg52.h>

#define uchar unsigned char
#define uint unsigned int

uchar code password[] = {'1', '2', 'A', 'B'};  // 正确密码
uchar code table[] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F, 0x77, 0x7C, 0x39, 0x5E, 0x79, 0x71};

void delay(uint xms){
    uint i, j;
    for(i = xms; i > 0; i--)
        for(j = 110; j > 0; j--);
}

void main(){
    uchar password_input[4];  // 输入密码
    uchar password_index = 0;  // 输入密码的下标
    uchar i;
    P1 = 0x00;  // 数码管段选
    P2 = 0xFF;  // 按键检测
    while(1){
        if(P2 != 0xFF){  // 按键检测
            delay(10);  // 消抖
            if(P2 != 0xFF){
                switch(P2){
                    case 0xFE: password_input[password_index] = '0'; break;
                    case 0xFD: password_input[password_index] = '1'; break;
                    case 0xFB: password_input[password_index] = '2'; break;
                    case 0xF7: password_input[password_index] = '3'; break;
                    case 0xEF: password_input[password_index] = '4'; break;
                    case 0xDF: password_input[password_index] = '5'; break;
                    case 0xBF: password_input[password_index] = '6'; break;
                    case 0x7F: password_input[password_index] = '7'; break;
                    case 0xFE: password_input[password_index] = '8'; break;
                    case 0xFD: password_input[password_index] = '9'; break;
                    case 0xFB: password_input[password_index] = 'A'; break;
                    case 0xF7: password_input[password_index] = 'B'; break;
                    case 0xEF: password_input[password_index] = 'C'; break;
                    case 0xDF: password_input[password_index] = 'D'; break;
                    case 0xBF: password_input[password_index] = 'E'; break;
                    case 0x7F: password_input[password_index] = 'F'; break;
                    default: password_input[password_index] = 0xFF; break;
                }
                P1 = table[password_input[password_index] - '0'];  // 显示输入字符
                password_index++;
                if(password_index == 4){  // 输入完4位密码
                    password_index = 0;
                    for(i = 0; i < 4; i++){
                        if(password_input[i] != password[i]){  // 密码错误
                            P1 = table['E' - '0'];
                            delay(1000);
                            break;
                        }
                    }
                    if(i == 4){  // 密码正确
                        P1 = table['P' - '0'];
                        delay(1000);
                    }
                }
            }
        }
    }
}