利用矩阵键盘扫描法、线反法的原理编写一段程序实现以下功能： 依次按下4*4 矩阵键盘上从第1 到第20 个键，同时在六位数码管上依次显示0、1、2、3、4、5、6、7、8、9、A、B、C、D、E、F。

以下是一个基于51单片机的程序，实现矩阵键盘扫描和六位数码管显示：

#include <reg51.h>

// 定义数码管控制端口
sbit DIG1 = P3^2;
sbit DIG2 = P3^3;
sbit DIG3 = P3^4;
sbit DIG4 = P3^5;
sbit DIG5 = P3^6;
sbit DIG6 = P3^7;

// 定义数码管段选端口（共阴极）
unsigned char code LED[16] = {
    0xC0,  // '0'
    0xF9,  // '1'
    0xA4,  // '2'
    0xB0,  // '3'
    0x99,  // '4'
    0x92,  // '5'
    0x82,  // '6'
    0xF8,  // '7'
    0x80,  // '8'
    0x90,  // '9'
    0x88,  // 'A'
    0x83,  // 'B'
    0xC6,  // 'C'
    0xA1,  // 'D'
    0x86,  // 'E'
    0x8E   // 'F'
};

// 定义矩阵键盘端口
sbit ROW1 = P2^0;
sbit ROW2 = P2^1;
sbit ROW3 = P2^2;
sbit ROW4 = P2^3;
sbit COL1 = P2^4;
sbit COL2 = P2^5;
sbit COL3 = P2^6;
sbit COL4 = P2^7;

// 定义变量
unsigned char key;  // 按键值
unsigned char digit[6] = {0};  // 数码管显示值

// 延时函数
void delay(unsigned int t) {
    unsigned int i, j;
    for (i = 0; i < t; i++) {
        for (j = 0; j < 125; j++);
    }
}

// 数码管扫描函数
void display(unsigned char *digit) {
    unsigned char i, j, temp;
    unsigned char code DIG[6] = {DIG1, DIG2, DIG3, DIG4, DIG5, DIG6};
    for (i = 0; i < 6; i++) {
        temp = digit[i];
        for (j = 0; j < 8; j++) {
            if (temp & 0x01) {
                DIG[i] = 1;
            } else {
                DIG[i] = 0;
            }
            temp >>= 1;
        }
    }
}

// 矩阵键盘扫描函数
unsigned char scan() {
    unsigned char i, j, k;
    unsigned char code table[4][4] = {
        {0, 1, 2, 3},
        {4, 5, 6, 7},
        {8, 9, 0xA, 0xB},
        {0xC, 0xD, 0xE, 0xF}
    };
    ROW1 = 0; ROW2 = 1; ROW3 = 1; ROW4 = 1;
    if (COL1 == 0) {delay(10); if (COL1 == 0) {i = 0; j = 0;}}
    if (COL2 == 0) {delay(10); if (COL2 == 0) {i = 0; j = 1;}}
    if (COL3 == 0) {delay(10); if (COL3 == 0) {i = 0; j = 2;}}
    if (COL4 == 0) {delay(10); if (COL4 == 0) {i = 0; j = 3;}}
    ROW1 = 1; ROW2 = 0; ROW3 = 1; ROW4 = 1;
    if (COL1 == 0) {delay(10); if (COL1 == 0) {i = 1; j = 0;}}
    if (COL2 == 0) {delay(10); if (COL2 == 0) {i = 1; j = 1;}}
    if (COL3 == 0) {delay(10); if (COL3 == 0) {i = 1; j = 2;}}
    if (COL4 == 0) {delay(10); if (COL4 == 0) {i = 1; j = 3;}}
    ROW1 = 1; ROW2 = 1; ROW3 = 0; ROW4 = 1;
    if (COL1 == 0) {delay(10); if (COL1 == 0) {i = 2; j = 0;}}
    if (COL2 == 0) {delay(10); if (COL2 == 0) {i = 2; j = 1;}}
    if (COL3 == 0) {delay(10); if (COL3 == 0) {i = 2; j = 2;}}
    if (COL4 == 0) {delay(10); if (COL4 == 0) {i = 2; j = 3;}}
    ROW1 = 1; ROW2 = 1; ROW3 = 1; ROW4 = 0;
    if (COL1 == 0) {delay(10); if (COL1 == 0) {i = 3; j = 0;}}
    if (COL2 == 0) {delay(10); if (COL2 == 0) {i = 3; j = 1;}}
    if (COL3 == 0) {delay(10); if (COL3 == 0) {i = 3; j = 2;}}
    if (COL4 == 0) {delay(10); if (COL4 == 0) {i = 3; j = 3;}}
    if (i == 255) {
        return 255;
    } else {
        return table[i][j];
    }
}

void main() {
    unsigned char i;
    while (1) {
        for (i = 0; i < 16; i++) {
            key = scan();  // 扫描键盘
            if (key != 255) {
                digit[0] = LED[i];
                digit[1] = LED[i];
                digit[2] = LED[i];
                digit[3] = LED[i];
                digit[4] = LED[i];
                digit[5] = LED[i];
                display(digit);  // 显示数字
                while (scan() != 255);  // 等待按键释放
            }
        }
    }
}

程序的原理是每次循环扫描矩阵键盘，如果检测到按键按下，则将相应的数字转换成段码，存储到`digit`数组中，然后调用`display`函数显示在数码管上。程序循环16次，依次显示0~F。