#include <reg52.h>

#define KEYPORT P0

sbit beep = P2^2;

unsigned char High;
unsigned char Low;

unsigned char code freq[][2]={ 
  0xD8,0xF7,//00440HZ 1   
  0xBD,0xF8,//00494HZ 2  
  0x87,0xF9,//00554HZ 3  
  0xE4,0xF9,//00587HZ 4    
  0x90,0xFA,//00659HZ 5     
  0x29,0xFB,//00740HZ 6     
  0xB1,0xFB,//00831HZ 7      
  0xEF,0xFB,//00880HZ `1
};

void timer0_init()
{
    EA = 1;
	TMOD |= 0x01;
	TH0 = 0;
	TL0 = 0;
	ET0 = 1;
	TR0 = 0;
}

void timer0_isr() interrupt 1
{
    TH0 = High;
	TL0 = Low;
	
	beep = ~beep;
}

void main()
{
	unsigned char num = 0;
    timer0_init();
	
	while(1)
	{		
		switch(KEYPORT )
		{
		    case 0xfe :
			{
			    num = 1;
				break;
			}
			case 0xfd :
			{
			    num = 2;
				break;
			}
			case 0xfb :
			{
			    num = 3;
				break;
			}
			case 0xf7 :
			{
			    num = 4;
				break;
			}
			case 0xef :
			{
			    num = 5;
				break;
			}
			case 0xdf :
			{
			    num = 6;
				break;
			}
			case 0xbf :
			{
			    num = 7;
				break;
			}
			case 0x7f :
			{
			    num = 8;
				break;
			}
			default :
			{
			    num = 0;
				break;
			}
		}
		
		if(num)
		{
		    High = freq[num - 1][1];
			Low = freq[num - 1][0];
			TR0 = 1;
		}
		else 
		{
		    TR0 = 0;
		}
	}
}