一个单片机应用与电子琴设计的源码参考！
#include <AT89X51.H>
unsigned char code table[]={0x3f,0x06,0x5b,0x4f,
                            0x66,0x6d,0x7d,0x07,
                            0x7f,0x6f,0x77,0x7c,
                            0x39,0x5e,0x79,0x71};
unsigned char temp;
unsigned char key;
unsigned char i,j;
unsigned char STH0;
unsigned char STL0;
unsigned int code tab[]={64021,64103,64260,64400,
                          64524,64580,64684,64777,
                          64820,64898,64968,65030,
                          65058,65110,65157,65178};

void main(void)
{
TMOD=0x01;
ET0=1;
EA=1;

while(1)
    {
      P3=0xff;
      P3_4=0;
      temp=P3;
      temp=temp & 0x0f;
      if (temp!=0x0f)
        {
          for(i=50;i>0;i--)
          for(j=200;j>0;j--);
          temp=P3;
          temp=temp & 0x0f;
          if (temp!=0x0f)
            {
              temp=P3;
              temp=temp & 0x0f;             
              switch(temp)
                {
                  case 0x0e:
                    key=0;
                    break;
                  case 0x0d:
                    key=1;
                    break;
                  case 0x0b:
                    key=2;
                    break;
                  case 0x07:
                    key=3;
                    break;
                }
              temp=P3;
              P1_0=~P1_0;
              P0=table[key];
              STH0=tab[key]/256;
              STL0=tab[key]%256;
              TR0=1;
              temp=temp & 0x0f;             
              while(temp!=0x0f)
                {
                  temp=P3;
                  temp=temp & 0x0f;             
                }
              TR0=0;
            }
        }

      P3=0xff;
      P3_5=0;
      temp=P3;
      temp=temp & 0x0f;
      if (temp!=0x0f)
        {
          for(i=50;i>0;i--)
          for(j=200;j>0;j--);
          temp=P3;
          temp=temp & 0x0f;
          if (temp!=0x0f)
            {
              temp=P3;
              temp=temp & 0x0f;             
              switch(temp)
                {
                  case 0x0e:
                    key=4;
                    break;
                  case 0x0d:
                    key=5;
                    break;
                  case 0x0b:
                    key=6;
                    break;
                  case 0x07:
                    key=7;
                    break;
                }
              temp=P3;
              P1_0=~P1_0;
              P0=table[key];
              STH0=tab[key]/256;
              STL0=tab[key]%256;
              TR0=1;
              temp=temp & 0x0f;             
              while(temp!=0x0f)
                {
                  temp=P3;
                  temp=temp & 0x0f;             
                }
              TR0=0;
            }
        }

      P3=0xff;
      P3_6=0;
      temp=P3;
      temp=temp & 0x0f;
      if (temp!=0x0f)
        {
          for(i=50;i>0;i--)
          for(j=200;j>0;j--);
          temp=P3;
          temp=temp & 0x0f;
          if (temp!=0x0f)
            {
              temp=P3;
              temp=temp & 0x0f;             
              switch(temp)
                {
                  case 0x0e:
                    key=8;
                    break;
                  case 0x0d:
                    key=9;
                    break;
                  case 0x0b:
                    key=10;
                    break;
                  case 0x07:
                    key=11;
                    break;
                }
              temp=P3;
              P1_0=~P1_0;
              P0=table[key];
              STH0=tab[key]/256;
              STL0=tab[key]%256;
              TR0=1;
              temp=temp & 0x0f;             
              while(temp!=0x0f)
                {
                  temp=P3;
                  temp=temp & 0x0f;             
                }
              TR0=0;
            }
        }

      P3=0xff;
      P3_7=0;
      temp=P3;
      temp=temp & 0x0f;
      if (temp!=0x0f)
        {
          for(i=50;i>0;i--)
          for(j=200;j>0;j--);
          temp=P3;
          temp=temp & 0x0f;
          if (temp!=0x0f)
            {
              temp=P3;
              temp=temp & 0x0f;             
              switch(temp)
                {
                  case 0x0e:
                    key=12;
                    break;
                  case 0x0d:
                    key=13;
                    break;
                  case 0x0b:
                    key=14;
                    break;
                  case 0x07:
                    key=15;
                    break;
                }
              temp=P3;
              P1_0=~P1_0;
              P0=table[key];
              STH0=tab[key]/256;
              STL0=tab[key]%256;
              TR0=1;
              temp=temp & 0x0f;             
              while(temp!=0x0f)
                {
                  temp=P3;
                  temp=temp & 0x0f;             
                }
              TR0=0;
            }
        }     
    }
}

void t0(void) interrupt 1 using 0
{
TH0=STH0;
TL0=STL0;
P1_0=~P1_0;
}