用矩阵按键输入“0~9”、独立按键输入运算符，数码管显示输入数据及结果，做一个简易的10000以内加、减、乘运算。

#include"STC12C5A60S2.H"

#define ON 0
#define OFF 1

sbit RS=P2^6;
sbit RW=P2^7;
sbit E=P4^4;

sbit Back_Light=P4^5;

sbit Buzz=P2^5;

unsigned char Key_Code[16]=
{
   0xe7,0xd7,0xb7,0x77,
    0xeb,0xdb,0xbb,0x7b,
    0xed,0xdd,0xbd,0x7d,
    0xee,0xde,0xbe,0x7e
};

unsigned char Num_TAB[10]="0123456789";

void Init_INT();

void Init_LCD();
void Set_xy(unsigned char x,unsigned char y);
void Wcom(unsigned char com);
void WDat(unsigned char Dat);
void Ready();

void Buzz_Start();
void Buzz_Stop();

void Delay();

void main()
{
   P4SW=0xFF;
   Back_Light=ON;

   P1=0xF0;        //这句不能漏，而且只能这样写，否则无法中断

   Init_LCD();
   Init_INT();

   while(1);
}

void Init_INT()
{
   TCON=0x00;
   EX0=1;
   EA=1;
}

void Init_LCD()
{
   Wcom(0x00);
   Wcom(0x06);
   Wcom(0x38);
   Wcom(0x0F);
   Set_xy(0,1);
}

void Read_Key() interrupt 0
{
   unsigned char Key,Key_H,Key_L;
   unsigned char i=0;

   Buzz_Start();

   P1=0x0F;       //用我这种带中断按键，反转是分先后的；别人的不用。
   if(P1!=0x0F)
   {
      Delay();
      if(P1!=0x0F)
      {
         Key_L=P1&0x0F;
      }
   }
   P1=0xF0;
   if(P1!=0xF0)
   {
      Delay();
      if(P1!=0xF0)
      {
         Key_H=P1&0xF0;
      }
   }         
   Key=Key_H|Key_L;

   for(i=0;i<10;i++)
   {
      if(Key==Key_Code[i])
      {
         WDat(Num_TAB[i]);
      }
   }

   while((P1&0xF0)!=0xF0);
   Buzz_Stop();
}

void Set_xy(unsigned char x,unsigned char y)
{
   if(y==1){Wcom(x|0x80);}
   if(y==2){Wcom(x|0xC0);}
}

void Wcom(unsigned char com)
{
   Ready();
   RS=0;
   RW=0;
   E=1;
   P0=com;
   E=0;
}

void WDat(unsigned char Dat)
{
   Ready();
   RS=1;
   RW=0;
   E=1;
   P0=Dat;
   E=0;
}

void Ready()
{
   unsigned char sta;

   P0=0xFF;
   RS=0;
   RW=1;
   do
   {
      E=1;
      sta=P0;
      E=0;
   }
   while(sta&0x80);
}

void Buzz_Start()
{
   Buzz=ON;
}

void Buzz_Stop()
{
   Buzz=OFF;
}

void Delay()
{
   unsigned char t=250;

   while(t--);
}