此程序的電路圖下載：http://m.raoushi.com/f/ks51.pdf 只需要看數碼管部分即可，其他部分可忽略掉.
#include <reg52.h> //stc89c51單片機頭文件
typedef unsigned char uchar;
typedef unsigned int uint;
typedef unsigned long ulong; //變量類型宏定義
sbit ENLED = P1^4;
sbit ADDR0 = P1^0;//管腳定義，作用為使能74hc138，讓38譯碼器開始工作
sbit ADDR1 = P1^1;
sbit ADDR2 = P1^2;
sbit ADDR3 = P1^3; //管腳定義，作用為選定38譯碼器輸出Y0-Y7，以便選定要顯示的數碼管（位選擇）
uchar led_char[] = {
0xC0, 0xF9, 0xA4, 0xB0,
0x99, 0x92, 0x82, 0xF8,
0x80, 0x90, 0x88, 0x83,
0xC6, 0xA1, 0x86, 0x8E}; //數碼管字符真值表 0-F
uchar led_buf[] = {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF}; //數碼管字符初始化，為關閉狀態
uchar cnt = 0; //T1定時器溢出計數
uchar key = 0; //數碼管動態掃描開關
ulong sec = 0; //時間變量
uchar hh = 8; //小時初值
uchar mm = 30; //分鐘初值
uchar ss = 40; //秒數初值
void main()
{
sec = hh *3600 + mm * 60 + ss;//時間計算公式
EA = 1; //打開中斷開關
ENLED = 0;
ADDR3 = 1; //使能74hc138，讓38譯碼器開始工作
TMOD = 0x10;//定時器工作模式設定
TH1 = 0xEE;
TL1 = 0x00;//定時初值設置
ET1 = 1; //打開定時器1中斷開關
TR1 = 1; //定時器1開始計時
while(1)
{
if(200 == cnt)
{
cnt = 0;
sec++;
if(sec < 86400)
{
led_buf[0] = led_char[sec%10];
led_buf[1] = led_char[sec%60/10];
led_buf[2] = led_char[sec%3600/60%10];
led_buf[3] = led_char[sec%3600/600];
led_buf[4] = led_char[sec/3600%10];
led_buf[5] = led_char[sec/3600/10]; //時間顯示字符計算
}
if(sec == 86400)
{
sec = 0;
}
}
}
}
void interruptTimer0() interrupt 3 //定時器1中斷服務程序
{
TH1 = 0xEE;
TL1 = 0x00; //定時初值設置
cnt++;
P0 = 0xFF; //數碼管消除鬼影
switch(key)
{
case 0: ADDR2 = 0;ADDR1 = 0;ADDR0 = 0;P0 = led_buf[0];key++;break;
case 1: ADDR2 = 0;ADDR1 = 0;ADDR0 = 1;P0 = led_buf[1];key++;break;
case 2: ADDR2 = 0;ADDR1 = 1;ADDR0 = 0;P0 = led_buf[2];key++;break;
case 3: ADDR2 = 0;ADDR1 = 1;ADDR0 = 1;P0 = led_buf[3];key++;break;
case 4: ADDR2 = 1;ADDR1 = 0;ADDR0 = 0;P0 = led_buf[4];key++;break;
case 5: ADDR2 = 1;ADDR1 = 0;ADDR0 = 1;P0 = led_buf[5];key = 0;break;
default:break;
} //數碼管動態掃描、顯示時間值
}