单片机：手动设定倒计时时间，0报警

首先显示”时.分“，K1时增加，K2分增加（如果不修改时分默认5分钟：300秒倒计时）

K3开始倒计时，显示秒倒计时，到时报警BEEP

K4停止报警，并返回到”时分“状态，又可以设置倒计时时间，来回循环 

#include<reg51.h>
#define uchar unsigned char;
#define uint unsigned int;
uchar position;           
uchar tt,bz=0,bza=1;             
uint second;       
uchar minute;
uchar hour;       
uchar code table[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90};//0--9
sbit smg_q = P2^0; 
sbit smg_b = P2^1; 
sbit smg_s = P2^2;
sbit smg_g = P2^3;
sbit key1=P3^2;                 
sbit key2=P3^3;
sbit key3=P3^4;
sbit key4=P3^5;
sbit led1=P1^0;
sbit led2=P1^1;
sbit led3=P1^2;
sbit led4=P1^3;
sbit led5=P1^4;
sbit led6=P1^5;
sbit beep=P2^5;
void keyscan();                   
void display(unsigned char hour,unsigned char minute);
void displaym(unsigned int second);
void delay(unsigned int timer);
void init();
void main()
{
     init();                                    
   while(1)
      {
       if(tt==20)
         { led1=~led1;led2=~led2;
                        tt=0;
          if(second==0 && bz==1)
              {
               while (bza==1)
                                 {
                                     beep=0;
                                     delay(100);
                                     beep=1;
                                     break;
                                 }
               }
                        else
                            second--;
           }
           keyscan();
                     if (bz==0)
           display(hour,minute);  
                        else
                            displaym(second);
          delay(1);
      }
    }
void keyscan()
{  if(key1==0)     
     {
      TR0=0;
      hour++;
      if(hour==24)
          hour=0;
      delay(200)        ;
      }
   if(key2==0)               
     {TR0=0;
      minute++;
     if(minute==60)
       minute=0;
     delay(200)        ;
     }
  if(key3==0)    
    {
            bz=1;
            bza=1;
     TR0=0;
            second=hour*3600+minute*60;
            if (second==0)
                second=300;
            delay(200)        ;
    TR0=1;
    }
  if(key4==0)          
   {
    beep=1;
         bz=0;
         bza=0;
         minute=0;
         TR0=0;
         led1=1;
         led2=1;
         second=0;
         hour=0;
         minute=0;
      
   }
}
void init()
{
    tt=0;
    bza=1;
    position=0;               
    second=0; 
    minute=0;        
    hour=0;   
    smg_q=1;
    smg_b=1;
    smg_s=1;
    smg_g=1;
    key1=1;
    key2=1;
    TMOD=0X01;  
    TH0=0x4c;        
    TL0=0x00;
    EA=1;                
    ET0=1;              
    TR0=0;              
}
void t0() interrupt 1
{
  TH0=0x4c;        
  TL0=0x00;
  tt++;

}
void display(unsigned char hour,unsigned char minute)
{     P0=0XFF;                             
      switch(position)
      {
       case 0:   smg_g=1;smg_q=0;P0=table[hour/10]; break;
       case 1:   smg_q=1;smg_b=0; P0=table[hour%10];if(tt>=10) P0&=0x7f; break;
       case 2:   smg_b=1;smg_s=0;P0=table[minute/10];break;
       case 3:   smg_s=1;smg_g=0;P0=table[minute%10];break;
       }
      position++;               
      if(position>3)
          position=0;      
}
void displaym(unsigned int second)
{     P0=0XFF;                             
      switch(position)
      {
       case 0:   smg_g=1;smg_q=0;P0=table[second/1000]; break;
       case 1:   smg_q=1;smg_b=0; P0=table[second/100%10]; break;
       case 2:   smg_b=1;smg_s=0;P0=table[second/10%10];break;
       case 3:   smg_s=1;smg_g=0;P0=table[second%10];if(tt>=10) P0&=0x7f;break;
       }
      position++;               
      if(position>3)
          position=0;      
}
void delay(unsigned int time)
{                
   unsigned int x,y;
   for(x=time;x>0;x--)
     for(y=110;y>0;y--);
}

 更新：显示四位以上的秒时：显示最后四位的秒数，第一位数码管右侧的点亮。如果不亮，则表明四位数码管能完整显示倒计时秒数
如下是更新的代码

#include<reg51.h>
#include <math.h>
#include <stdio.h>
#define uchar unsigned char;
#define uint unsigned int;
uchar position;           
uchar tt,bz=0,bza=1,bk;             
uint second,ws,i=0,ws1;       
uchar minute;
uchar hour; 
char cc[10];
uchar code table[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90};//0--9
sbit smg_q = P2^0; 
sbit smg_b = P2^1; 
sbit smg_s = P2^2;
sbit smg_g = P2^3;
sbit key1=P3^2;                 
sbit key2=P3^3;
sbit key3=P3^4;
sbit key4=P3^5;
sbit led1=P1^0;
sbit led2=P1^1;
sbit led3=P1^2;
sbit led4=P1^3;
sbit led5=P1^4;
sbit led6=P1^5;
sbit beep=P2^5;
sbit dian=P0^7;  
unsigned int jcws(unsigned int a);
void keyscan();                   
void display(unsigned char hour,unsigned char minute);
void displaym(unsigned int second);
void delay(unsigned int timer);
void init();
void main()
{
     init();                                    
   while(1)
      {
       if(tt==20)
         { led1=~led1;led2=~led2;
                        tt=0;
          if(second==0 && bz==1)
              {
               while (bza==1)
                                 {
                                     beep=0;
                                     delay(100);
                                     beep=1;
                                     break;
                                 }
               }
                        else
                            second--;
           }
           keyscan();
                     if (bz==0)
           display(hour,minute);  
                        else
                            displaym(second);
          delay(2);
      }
    }
unsigned int jcws(unsigned int a)
{
    sprintf(cc,"%d",a);
    i=0;
    while(cc[i++] != '\0');
    return i-1;
}
void keyscan()
{  if(key1==0 && bz==0)     
     {
      TR0=0;
      hour++;
      if(hour==24)
          hour=0;
            display(hour,minute); 
      delay(200)        ;
      }
   if(key2==0 && bz==0)               
     {TR0=0;
      minute++;
     if(minute==60)
       minute=0;
         display(hour,minute); 
     delay(200)        ;
     }
  if(key3==0)    
    {
            bz=1;
            bza=1;
     TR0=0;
            second=hour*3600+minute*60;
            if (second==0)
            {
                hour=0;minute=0;
                second=300;}
            //delay(200)        ;
    TR0=1;
    }
  if(key4==0)          
   {
    beep=1;
         bz=0;
         bza=0;
         minute=0;
         TR0=0;
         led1=1;
         led2=1;
         second=0;
         hour=0;
         minute=0;
      
   }
}
void init()
{
    tt=0;
    bza=1;
    position=0;               
    second=0; 
    minute=0;        
    hour=0;   
    smg_q=1;
    smg_b=1;
    smg_s=1;
    smg_g=1;
    key1=1;
    key2=1;
    TMOD=0X01;  
    TH0=0x4c;        
    TL0=0x00;
    EA=1;                
    ET0=1;              
    TR0=0;              
}
void t0() interrupt 1
{
  TH0=0x4c;        
  TL0=0x00;
  tt++;

}
void display(unsigned char hour,unsigned char minute)
{     P0=0XFF;
            switch(position)
      {
       case 0:   smg_g=1;smg_q=0;P0=table[hour/10]; break;
       case 1:   smg_q=1;smg_b=0; P0=table[hour%10]; dian=0x00; break;
       case 2:   smg_b=1;smg_s=0;P0=table[minute/10];break;
       case 3:   smg_s=1;smg_g=0;P0=table[minute%10];break;
       }
      position++;               
      if(position>3)
          position=0;      
}
void displaym(unsigned int second)
{     P0=0XFF;  
            ws=jcws(second);    
      switch(position)
      {
       case 0:   smg_g=1;smg_q=0;
                                P0=table[second/1000%10]; 
                                 if (ws>4)
                                 {
                                        dian=0x00;
                                        }
                                 else
                                 {dian=0xff;
                                                         
                                 }
                                 //delay(2);
                                 break;
                //case 0:   smg_g=1;smg_q=0;P0=table[second/1000%10]; break;
       case 1:   smg_q=1;smg_b=0; P0=table[second/100%10];; break;
       case 2:   smg_b=1;smg_s=0;P0=table[second/10%10];break;
       case 3:   smg_s=1;smg_g=0;P0=table[second%10];if(tt>=10) P0&=0x7f;break;
       }
      position++;               
      if(position>3)
          position=0;      
}
void delay(unsigned int time)
{                
   unsigned int x,y;
   for(x=time;x>0;x--)
     for(y=110;y>0;y--);
}