修改程序使数码管暂停计数：#include <REGX51.H> unsigned char x[]={0xC0,0xF9,0XA4,0XB0,0X99,0X92,0X82,0XF8,0X80,0X90,0xBF,0xff}; unsigned char sec=0,min=0,hour=0; unsigned char a=0; void delay(unsigned int xms) //@12.000MHz { unsigned char i, j; while(xms) { i = 2; j = 239; do { while (--j); } while (--i); xms=xms-1; } } void fun(unsigned char location,number) { switch(location) { case 0:P3=0x01;break; case 1:P3=0x02;break; case 2:P3=0x04;break; case 3:P3=0x08;break; case 4:P3=0x10;break; case 5:P3=0x20;break; case 6:P3=0x40;break; case 7:P3=0x80;break; } P0=x[number]; delay(2); P0=0xff; } void main(void) { TMOD=0X01; TL0=(65536-10000)%256; TH0=(65536-10000)/256; TR0=1; ET0=1; EA=1; while(1) { if(P1_2==0) { delay(20); while(P1_2==0); delay(20); sec++; } if(P1_1==0) { delay(20); while(P1_1==0); delay(20); min++; } if(P1_0==0) { delay(20); while(P1_0==0); delay(20); hour++; } if(P2_0==0) { delay(20); while(P2_0==0); delay(20); sec=0; min=0; hour=0; } fun(0,sec%10); fun(1,sec/10); fun(2,10); fun(3,min%10); fun(4,min/10); fun(5,10); fun(6,hour%10); fun(7,hour/10); } } void timer0_start(void) interrupt 1 { TL0=(65536-10000)%256; TH0=(65536-10000)/256; a++; if(a==100) { sec++; a=0; if(sec==60) { min++; sec=0; } if(min==60) { hour++; min=0; } } if(sec==20&&min==1&&hour==0) { P2_0=1; P2_1=0; } }

在程序中加入一个标志变量，代表是否暂停计数。可以在按下按钮时修改该变量的值，使数码管停止计数。修改后的程序如下所示：

#include <REGX51.H> 

unsigned char x[]={0xC0,0xF9,0XA4,0XB0,0X99,0X92,0X82,0XF8,0X80,0X90,0xBF,0xff}; 
unsigned char sec=0,min=0,hour=0; 
unsigned char a=0; 
bit pause_count = 0; //新增的标志变量

void delay(unsigned int xms) //@12.000MHz 
{ 
    unsigned char i, j; 
    while(xms) 
    { 
        i = 2; 
        j = 239; 
        do 
        { 
            while (--j); 
        } while (--i); 
        xms=xms-1; 
    } 
} 

void fun(unsigned char location,number) 
{ 
    switch(location) 
    { 
        case 0:P3=0x01;break; 
        case 1:P3=0x02;break; 
        case 2:P3=0x04;break; 
        case 3:P3=0x08;break; 
        case 4:P3=0x10;break; 
        case 5:P3=0x20;break; 
        case 6:P3=0x40;break; 
        case 7:P3=0x80;break; 
    } 
    P0=x[number]; 
    delay(2); 
    P0=0xff; 
} 

void main(void) 
{ 
    TMOD=0X01; 
    TL0=(65536-10000)%256; 
    TH0=(65536-10000)/256; 
    TR0=1; 
    ET0=1; 
    EA=1; 

    while(1) 
    { 
        if(P1_2==0) 
        { 
            delay(20); 
            while(P1_2==0); 
            delay(20); 
            sec++; 
        } 
        if(P1_1==0) 
        { 
            delay(20); 
            while(P1_1==0); 
            delay(20); 
            min++; 
        } 
        if(P1_0==0) 
        { 
            delay(20); 
            while(P1_0==0); 
            delay(20); 
            hour++; 
        } 
        if(P2_0==0) 
        { 
            delay(20); 
            while(P2_0==0); 
            delay(20); 
            sec=0; 
            min=0; 
            hour=0; 
        } 
        if(!pause_count) //新增的判断语句
        {
            fun(0,sec%10); 
            fun(1,sec/10); 
            fun(2,10); 
            fun(3,min%10); 
            fun(4,min/10); 
            fun(5,10); 
            fun(6,hour%10); 
            fun(7,hour/10); 
        }
    } 
} 

void timer0_start(void) interrupt 1 
{ 
    TL0=(65536-10000)%256; 
    TH0=(65536-10000)/256; 
    a++; 
    if(a==100) 
    { 
        sec++; 
        a=0; 
        if(sec==60) 
        { 
            min++; 
            sec=0; 
        } 
        if(min==60) 
        { 
            hour++; 
            min=0; 
        } 
    } 
    if(sec==20&&min==1&&hour==0) 
    { 
        P2_0=1; 
        P2_1=0; 
    } 
}