Proteus仿真        
P3.0輸出占空比    
T+、T-設置占空比時間，每按一次加或減100ms   
R+、R-設置占空比加減1%      初始為100ms 占空比50%       
數碼管前兩位顯示時間單位s，后兩位顯示占空比單位%      
示波器顯示

使用定時器，避免了數碼管顯示和按鍵掃描延時，實現占空比實時輸出。避免因延時等待。 12MHz晶振程序如下

#include <reg52.h>                                         
#define        CLOCK        12000L
#define        Fosc        12000000L
#define        TMR        1
#define        TMR_BASE        (unsigned int)(65536-(Fosc*TMR/CLOCK))
#define        TMR_BASEH        TMR_BASE/0x100
#define MASK 0xaa
#define AddT 0xa8 
#define CutT 0xa2
#define AddR 0x8a
#define CutR 0x2a
sbit OUT=P3^0;
code unsigned char Num[10]={0xc0,0xf9,0xa4,0x30,0x99,0x92,0x82,0xf8,0x80,0x90};
bit        T1ms_Fg;
void Timer0_interrupt(void)  interrupt 1
{
        TR0=0;
        TH0=TMR_BASEH;
        TL0+=TMR_BASE;
        TR0=1;
        T1ms_Fg=1;
}
void TMR0_Init(void)
{
        TMOD=0x01;
        TH0=TMR_BASEH;
        TL0=TMR_BASE;
        TR0=1;
        ET0=1;
}        
bit        Tmr_1ms_Fg,        
        Tmr_10ms_Fg,        
        Tmr_100ms_Fg;
unsigned char        T100ms_count=10;         
void timer(void)
{
          Tmr_1ms_Fg=0;
          Tmr_10ms_Fg=0;        
        Tmr_100ms_Fg=0;        
        if (T1ms_Fg)
        {
                T1ms_Fg=0;        
                Tmr_1ms_Fg=1;
                --T100ms_count;        
                if (T100ms_count%10==0)
                {
                        Tmr_10ms_Fg=1;         
                }
                if (T100ms_count==0)
                {
                        T100ms_count=10;
                        Tmr_100ms_Fg=1;         
                }
        }
}        
unsigned char T=1,R=50;
void diaplay(void)
{
   static unsigned char status=0;
   if(!Tmr_10ms_Fg)return;
   P0=0xff; 
   P2=0x01<<status;
   switch(status)
   {
            case 0:
           P0=Num[T/10]&0x7f;
           status++;
           break; 
            case 1:
           P0=Num[T%10];
           status=4;
           break;  
            case 4:
           P0=Num[R/10];
           status++;
           break;
            case 5:
           P0=Num[R%10];
           status=0;
           break;
   }
}
void key(void)
{                 
        static unsigned char dat,statue=0;
        if(!Tmr_10ms_Fg)return;
        dat=P3&MASK;
        if(dat==MASK)return;
        statue++;
        if(statue<16)return;
        statue=0;
        switch(dat)
        {
          case AddT:
            T++;
                if(T>30)T=1;
            break; 
          case CutT:
            T--;
                if(T<1)T=30;
            break; 
          case AddR:
            R++;
                if(R>99)R=1;
            break; 
          case CutR:
            R--;
                if(R<1)R=99;
            break;
        }
}
bit Duty_fg=1;
void duty(void)
{
   static unsigned int r=50;
   if(!Tmr_1ms_Fg)return;
   if(--r)return;
   OUT=Duty_fg;
   if(Duty_fg)r=R*T;
   else r=(100-R)*T;
   Duty_fg=~Duty_fg; 
}
void main(void)
{ 
   TMR0_Init();
   EA=1;
        while(1)
        {
          timer();
          diaplay();
          duty();
          key();
        }
}