按键按一次，蜂鸣器响一次 ，LCD1602同步。

#include <REGX52.H>
#include <INTRINS.H>unsigned int keynum;
sbit RS=P3^0; //**
sbit RW=P3^1;  //**
sbit E=P3^2; //**
sbit buzzer=P1^5;
void delay(unsigned int n)//1ms  
{unsigned char a,b,c,m;for(m=n;m>0;m--)for(c=1;c>0;c--)for(b=142;b>0;b--)for(a=2;a>0;a--);
}
unsigned char key()
{unsigned char keynumber=0;if(P1_0==0){delay(20);while(P1_0==0);delay(20);keynumber=1;}if(P1_1==0){delay(10);while(P1_1==0);delay(10);keynumber=2;}if(P1_2==0){delay(10);while(P1_2==0);delay(10);keynumber=3;}if(P1_3==0){delay(20);while(P1_3==0);delay(20);keynumber=4;}return keynumber;
}
void writedat(unsigned char dat)
{RS=1;RW=0;E=0;P2=dat;delay(10);	  //看情况要不要延时E=1;E=0;
}
void writecom(unsigned char com)
{RS=0;RW=0;E=0;P2=com;delay(10);E=1;E=0;
}
void initlcd()
{writecom(0x38);writecom(0x0c);writecom(0x06);writecom(0x01);
}
void LCD_SetCursor(unsigned char Line,unsigned char Column)
{if(Line==1){writecom(0x80|(Column-1));}else if(Line==2){writecom(0x80|(Column-1+0x40));}
}
int LCD_Pow(int X,int Y)
{unsigned char i;int Result=1;for(i=0;i<Y;i++){Result*=X;}return Result;
}
void LCD_ShowNum(unsigned char Line,unsigned char Column,unsigned int Number,unsigned char Length)
{unsigned char i;LCD_SetCursor(Line,Column);for(i=Length;i>0;i--){writedat(Number/LCD_Pow(10,i-1)%10+'0');}
}
void buzzer_time(unsigned int ms)
{unsigned int i;for(i=0;i<ms;i++){buzzer=!buzzer;delay(1);			   //每隔1ms翻转一次，周期为2ms，频率500hz}	
}
void main()
{initlcd();while(1){keynum=key();if(keynum){buzzer_time(500);LCD_ShowNum(1,1,keynum,1);	}	}
}

《小星星》乐谱 

#include <REGX52.H>
#include <INTRINS.H>
unsigned int freqtable[]={63628,63731,63835,63928,64021,64103,64185,64260,64331,64400,64463,64528,64580,64633,64684,64732,64777,64820,64860,64898,64934,64968,65000,65030,65058,65085,65110,65134, 65157,65178,65198,65217,65235,65252,65268,65283,};
unsigned char music[]={
12,4,
12,4,
19,4,
19,4,
21,4,
21,4,
19,4+4,
17,4,
17,4,
16,4,
16,4,
14,4,
14,4,
12,4+4,
};
unsigned char freqselect,musicselect;
unsigned int keynum;
sbit RS=P3^0; //**
sbit RW=P3^1;  //**
sbit E=P3^2; //**
sbit buzzer=P1^5;
void delay(unsigned int t)
{unsigned int i=0,j=0;for(i=0;i<t;i++){for(j=0;j<120;j++);}
}void main()
{buzzer=0;inittimer();//initlcd();while(1){freqselect=music[musicselect];musicselect++;delay(125*music[musicselect]);musicselect++;TR0=0;delay(5);TR0=1;}
}
void time0() interrupt 1//定时器0中断函数
{TH0=freqtable[freqselect]/256; //初值=65536-1000=64536=FC18H,定时1msTL0=freqtable[freqselect]%256;buzzer=!buzzer;///1ms翻转一次，相当于一个周期为2ms，频率500hz
}