C源代碼：

#include <reg52.h>

/*定義字型字位口*/
#define DIGPORT P2
#define WORDPORT P0

/*定義鍵盤口*/
#define KEYPORT P1

#define uint unsigned int
#define uchar unsigned char
#define uong unsigned long

sbit P_7=P3^7; //PWM信號輸出

bit OVER;
uint k,dt;
uong KEYNUM; 
uchar qu,NUM;

void Delay(uint ms)
{
   while(--ms);
}


void timer0(void) interrupt 1 using 1
{
  TL0=-(10248%256);
  TH0=-(10248%256);
  NUM+=1;
  if(NUM>=10){
    TR1=0;
    TR0=0;
    OVER=1;
  }
}

uint CK(void)
{
  uint number=0;
  P_7=1;
  OVER=0;NUM=0;
  EA=1;ET0=1;
  TH0=(10203/256);
  TH0=(10203%256);
  TH1=0;
  TL1=0;
  TMOD=0x51;
  TR0=1;
  TR1=1;
  Delay(dt);
  P_7=0;
  while (!OVER);
  OVER=0;
  number=TH1*256+TL1;
  return(number);
}

void Display_LED(uong nu)
{
  uint ii=0;
  uong aa,bb;
  uint xx[]={-0x10,-0x10,-0x10,-0x10,-0x10,-0x10,-0x10,-0x10};
  do
  {
    bb=nu/10;
    aa=nu-bb*10;
    xx[ii]=aa;
    nu=bb;ii++;
  }while(nu>0);
  DIGPORT=0xf0; WORDPORT=0x30+xx[0];
  DIGPORT=0xf1; WORDPORT=0x30+xx[1];
  DIGPORT=0xf2; WORDPORT=0x30+xx[2];
  DIGPORT=0xf3; WORDPORT=0x30+xx[3];
  DIGPORT=0x0f; WORDPORT=0x30+xx[4];
  DIGPORT=0x1f; WORDPORT=0x30+xx[5];
  DIGPORT=0x2f; WORDPORT=0x30+xx[6];
  DIGPORT=0x3f; WORDPORT=0x30+xx[7];
}

void getkey()
{
qu=0;k=0;
KEYNUM=0;
do
{
  switch(KEYPORT)
  {
    case 0xbd:
      KEYNUM=KEYNUM*10;
      break;
    case 0xf6:
       KEYNUM=KEYNUM*10+1;
       break;
    case 0xf5:
       KEYNUM=KEYNUM*10+2;
       break;
    case 0xf3:
       KEYNUM=KEYNUM*10+3;
       break;
    case 0xee:
       KEYNUM=KEYNUM*10+4;
       break;
    case 0xed:
       KEYNUM=KEYNUM*10+5;
       break;
    case 0xeb:
       KEYNUM=KEYNUM*10+6;
       break;
    case 0xde:
       KEYNUM=KEYNUM*10+7;
       break;
    case 0xdd:
       KEYNUM=KEYNUM*10+8;
       break;
    case 0xdb:
       KEYNUM=KEYNUM*10+9;
       break;
   case 0xbe:
       KEYNUM=KEYNUM/10;
       break;
    case 0xbb:
      qu=1;
   }
   Delay(6000);
   Delay(6000);
   Delay(6000);
   Delay(6000);
   Delay(6000);
   Delay(6000);
   Delay(6000);
   Delay(6000);

   if(KEYNUM>100000000) break;
   Display_LED(KEYNUM);
 }while(qu==0);
}


void main(void)
{
  uong f;
  P_7=0;
  dt=1000;
  getkey();
  for(;;){
    f=0;
    f=CK()*12;
    Display_LED(f);
    if((f>KEYNUM)&&(dt>100)) dt=dt-(f-KEYNUM)/10;
    if((f<KEYNUM)&&(dt<6400)) dt=dt+(KEYNUM-f)/10;
  }
}