程序：

//共阴数码管
//0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71 //0-F的码表

//共阳数码管
//0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e //0-F的码表
								
#include "reg51.h"

#define SMG_PORT P0
#define KEY_PORT P2

#define uchar unsigned char

sbit LED=P1^0;

uchar code dis[17]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0x00};
//unsigned char code dis[16]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e};

void delay_ms(int a)
{
	int i=0,j=0;
	for(i=0;i<a;i++)
		for(j=0;j<118;j++);// 1ms
}

uchar Scan_Button(void)
{
	uchar i=0,count=0,temp, LINE[4] = {0xef, 0xdf, 0xbf, 0x7f};	//1110 1111

	KEY_PORT=0xff;
		
	for(i=0;i<4;i++)
	{
		KEY_PORT = LINE[i];	//
		delay_ms(20);
		temp = 0x01;                                                                                                                                                                   
		for(count=0;count<4;count++)
		{
			if(!(KEY_PORT&temp))//按键按下时!P2&temp为1，进入if // 1110 1110 & 0000 0010 =0000 0000
			{
				SMG_PORT=dis[count+i*4];
				while(!(KEY_PORT&temp)); //松开
				return (count+i*4);
			}
			temp <<= 1;//左移一位 // 0x02 0000 0010
		}
	}	
	SMG_PORT=dis[16];
	return 0xff;	
}


int main(void)
{
	LED=1;
	while(1)
	{
		if(0xff!=Scan_Button())
			LED=0;
		else
			LED=1;
	}
	return 0;
}