keil uvision2实现被转换的ASCII码十进制数45、12（即34H，35H，31H，32H）存放在0500H～0503H单元中，转换的结果存放在20H，21H单元中。

实现步骤如下：

1. 定义变量并初始化

unsigned char ascii[4] = {0x34, 0x35, 0x31, 0x32}; // 被转换的ASCII码
unsigned char result[2] = {0}; // 转换结果，初始值为0

2. 进行ASCII码到十进制数的转换

result[0] = (ascii[0] - 0x30) * 10 + (ascii[1] - 0x30); // 转换十位数
result[1] = (ascii[2] - 0x30) * 10 + (ascii[3] - 0x30); // 转换个位数

3. 存储转换结果

*(unsigned char*)0x0500 = ascii[0]; // 存储被转换的ASCII码
*(unsigned char*)0x0501 = ascii[1];
*(unsigned char*)0x0502 = ascii[2];
*(unsigned char*)0x0503 = ascii[3];
*(unsigned char*)0x0020 = result[0]; // 存储转换结果
*(unsigned char*)0x0021 = result[1];

完整代码如下：

void main()
{
    unsigned char ascii[4] = {0x34, 0x35, 0x31, 0x32}; // 被转换的ASCII码
    unsigned char result[2] = {0}; // 转换结果，初始值为0
    
    result[0] = (ascii[0] - 0x30) * 10 + (ascii[1] - 0x30); // 转换十位数
    result[1] = (ascii[2] - 0x30) * 10 + (ascii[3] - 0x30); // 转换个位数
    
    *(unsigned char*)0x0500 = ascii[0]; // 存储被转换的ASCII码
    *(unsigned char*)0x0501 = ascii[1];
    *(unsigned char*)0x0502 = ascii[2];
    *(unsigned char*)0x0503 = ascii[3];
    *(unsigned char*)0x0020 = result[0]; // 存储转换结果
    *(unsigned char*)0x0021 = result[1];
}