P3复制0XF0 这样对的吗？

各位高手老师，P3=0xf0; temp=P3;  //赋值给P3口
        temp=temp&0xf0;// 与的值
        if(temp!=0xf0)      是否相等？？我在程序里，注解了下·~~~我不是非常明白
 请各位老师，点评一下~~~~~，这程序是  网上某写的。但程序 运行正常~~~，但是键盘释放检测 ，没有~~~

#include<reg52.h>
#define uchar unsigned char //宏定义
#define uint unsigned int
sbit dula=P2^6;  //段声明
sbit wela=P2^7;// 位声明
uchar disnum,temp,key,num;
uchar code table_du[]={
0x3f,0x06,0x5b,0x4f,0x66,0x6d,
0x7d,0x07,0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71,0};

delay(uchar);
uchar keyscan();//键盘程序

void main() //主函数
{   
    disnum=16;
    wela=1;
    P0=0XFE;
    wela=0;
    while(1)
    {
    num=keyscan();   
    P0=table_du[num];
    dula=1;
    dula=0;
   
    }
   
}

uchar keyscan() //键盘扫描程序
{
    P3=0xf0;         //定义个变量
        temp=P3;  //赋值给P3口
        temp=temp&0xf0;// 与的值
        if(temp!=0xf0)// 确定不等于0xf0,但实际是相等的，
        {           //实际他应该退出的呀?  （因为是相等的，退出！各位高手老师，这样写对的吗？）    帮我分析下，

//谢谢！！！！！

            delay(10);    //延时10秒，去抖
            if(temp!=0xf0) //再次确定不相等，执行下一条指令
            {
                temp=P3;
                temp=temp|0X0f;
                P3=temp;
                key=P3;
                switch(key)
                {
                    case 0xee:disnum=0;
                            break;
                    case 0xde:disnum=1;
                            break;
                    case 0xbe:disnum=2;
                            break;
                    case 0x7e:disnum=3;
                            break;
                    case 0xed:disnum=4;
                            break;
                    case 0xdd:disnum=5;
                            break;
                    case 0xbd:disnum=6;
                            break;
                    case 0x7d:disnum=7;
                            break;
                    case 0xeb:disnum=8;
                            break;
                    case 0xdb:disnum=9;
                            break;
                    case 0xbb:disnum=10;
                            break;
                    case 0x7b:disnum=11;
                            break;
                    case 0xe7:disnum=12;
                            break;
                    case 0xd7:disnum=13;
                            break;
                    case 0xb7:disnum=14;
                            break;
                    case 0x77:disnum=15;
                            break;
                }
            }
        }
return disnum;  //返回值
}

delay(uchar x)//延时函数
{
    uchar a,b;
    for(a=x;a>0;a--)
        for(b=200;b>0;b--);

}