程序如下:

#include <AT89X51.H>
#define uchar unsigned char
#define uint unsigned int 
uchar code dispcode[]={0x81,0x9f,0xa4,0x8c,0x9a,0xc8,0xc0,0x9d,0x80,0x88};
uchar code DATA[]={0xfc,0x92,0x98,0xac,0x89,0x01,0x5c,0x80,0x88};
uchar dispbitcode[]={0xfe,0xfd,0xfb,0xf7};
uchar dispbuf[8]={0,0,0,0}; 
uchar dispbitcnt; 
uchar second,minite,hour,day; 
uchar clockhour,clockminite;
uint tcnt; 
uchar mstcnt; 
uchar t; 
uint a;
//上面的是定义各个变量和数码管缓存
void yanshi(uint t)
{
for(;t>0;t--);
}//延时子程序
void beep()
{
while(hour<clockhour){
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<5000;a++)
{yanshi(6);
P1_4=~P1_4;}
if(P3_6==0){break;}}
while(minite<clockminite){
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<5000;a++)
{yanshi(6);
P1_4=~P1_4;}
if(P3_6==0){break;}}}//报警子程序(P1.4接的是BEEP,P3.6为O时跳出)
void baojing()
{
if(P1_7==0){
yanshi(500);
if(P1_7==0){
while(1){
if(P1_7==1){
while(1){
beep();
if(P3_6==0)
{break;}}}
if(P3_6==0){break;}}}}}//报警执行子程序(用P1.7做信号检测脚,同样当P3.6为0时跳出)
void clock()
{
if(P3_3==0){yanshi(500); 
if(P3_3==0){clockminite++;
if(clockminite==60)
{clockminite=0;} 
dispbuf[3]=clockminite%10; 
dispbuf[2]=clockminite/10;              
while(P3_3==0);}} 
if(P3_6==0){yanshi(500); 
if(P3_6==0){clockhour++; 
if(clockhour==24){clockhour=0;} 
dispbuf[1]=clockhour%10; 
dispbuf[0]=clockhour/10; 
while(P3_6==0);}}}//设定闹钟子程序
void key()
{
if(P3_6==0){yanshi(500); 
if(P3_6==0){second++;
if(second==60){second=0;}            
while(P3_6==0);}} 
if(P3_5==0){yanshi(1000); 
if(P3_5==0){minite++; 
if(minite==60){minite=0;} 
dispbuf[3]=minite%10; 
dispbuf[2]=minite/10; 
while(P3_5==0);}} 
if(P3_7==0){yanshi(500); 
if(P3_7==0){hour++; 
if(hour==24){hour=0;} 
dispbuf[1]=hour%10; 
dispbuf[0]=hour/10; 
while(P3_7==0);}}
if(P3_4==0){yanshi(500); 
if(P3_4==0){day++; 
if(day==7){day=0; }
P2=DATA[day]; 
while(P3_4==0);}}
}//设定时间子程序
void laozhong()
{
if(hour==clockhour){
if(minite==clockminite){
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<1000;a++)
{yanshi(5);
P1_4=~P1_4;}
for(a=0;a<5000;a++)
{yanshi(6);
P1_4=~P1_4;}}}}//闹钟子程序
void display()
{
dispbuf[3]=minite%10; 
dispbuf[2]=minite/10; 
dispbuf[1]=hour%10; 
dispbuf[0]=hour/10;
P2=DATA[day];
}//显示子程序
void displayclock()
{
dispbuf[7]=clockminite%10; 
dispbuf[6]=clockminite/10; 
dispbuf[5]=clockhour%10; 
dispbuf[4]=clockhour/10;
}//闹钟显示子程序
void time()
{
tcnt++; 
if(tcnt==4000){tcnt=0;
second++;
if(second==60){second=0; 
minite++;
if(minite==60){minite=0; 
hour++;
if(hour==24){hour=0;
day++;
if(day==7){day=0;}}}}
display();}}//时间子程序
void t0(void) interrupt 1 using 0 
{
mstcnt++; 
if(mstcnt==4){mstcnt=0; 
P0=dispcode[dispbuf[dispbitcnt]]; 
P1=dispbitcode[dispbitcnt]; 
P2=DATA[day];
dispbitcnt++;}
if(dispbitcnt==4){dispbitcnt=0;}
time();displayclock();}//中断
void main(void) 
{ 
TMOD=0x02; 
TH0=0x06; 
TL0=0x06; 
TR0=1; 
ET0=1; 
EA=1;
while(1)
{
key();clock();
if(P1_6==0)
{while(1){laozhong();
if(P3_6==0){break;}}}
if(P3_2==0){yanshi(10000);
if(P3_2==0){while(1)
{baojing();
if(P3_6==0)
{break;}
}}}}}
//S1：启动报警器(P3.2)
//S2: clock minite 加(P3.3)
//S3: 星期加(P3.4)
//S4：time minite 加(P3.5)
//S5: clock hour 加/退出报警器(P3.6)
//S6：time hour 加(P3.7)
//P1-7为信号检测脚