C51中4X4键盘扫描（非反转法）

#include <reg52.h>

#define uchar unsigned char
#define uint unsigned int

uchar KEYIN;

void DelayMs(uint ms);                 //延时函数声明；
uchar KeyPress(void);                  //按键按下检测函数声明；
uchar KeyScan(void);                   //键值扫描函数声明；

void main(void)
{
    while (1)
    {
        if (KeyPress())
        {
            P0 = KeyScan();
            while (KeyPress());
        }
    }
}

void DelayMs(uint ms)               //11.0592MHZ 约为1.007MS; 
{
    uint x,y;
    for(x=ms;x>0;x--)                        
    {
        for(y=113;y>0;y--);
    }
}

uchar KeyPress(void)
{
    uchar keypress;
    P1 = 0xF0;                                     
    keypress = P1;
    if (keypress == 0xF0)
    {
        return 0;
    }
    else 
    {
        KEYIN = keypress;
        return 1;
    }
}

uchar KeyScan(void)
{
    uchar keyout,index,keycode,keyvalue;
    DelayMs(20);
    P1 = 0xF7;
    index = 0;
    if (KeyPress())
    {
        while (1)
        {
            P1 = (0xF7 >> index) | 0xF0; //I/O端口不能做为中间变量，如temp = (P1 >> index) 单片机随时读取IO的变化，会导致程序有瞬间错误产生；
            index++;
            index = index & 0x03;
            keyout = P1 & 0x0F;
            if ((P1 & 0xF0) != 0xF0)
            {
                keycode = KEYIN + keyout;
                break;  
            }

        }
        switch (keycode)
        {
            case 0x77 : keyvalue = 0xC0;     break;
            case 0x7B : keyvalue = 0xF9;     break;
            case 0x7D : keyvalue = 0xA4;     break;
            case 0x7E : keyvalue = 0xB0;     break;

            case 0xB7 : keyvalue = 0x99;     break;
            case 0xBB : keyvalue = 0x92;     break;
            case 0xBD : keyvalue = 0x82;     break;
            case 0xBE : keyvalue = 0xF8;     break;

            case 0xD7 : keyvalue = 0x80;     break;
            case 0xDB : keyvalue = 0x90;     break;
            case 0xDD : keyvalue = 0x88;     break;
            case 0xDE : keyvalue = 0x83;     break;

            case 0xE7 : keyvalue = 0xC6;     break;
            case 0xEB : keyvalue = 0xA1;     break;
            case 0xED : keyvalue = 0x86;     break;
            case 0xEE : keyvalue = 0x8E;     break;
            default : keyvalue = 0xFF;
        }
    }
    else
    {
        keyvalue = 0xFF;
    }
    return keyvalue;
}