#include<8051.h>

unsigned char PWMH;
unsigned char PWM;
unsigned char COUNTER;
bit dflg;

void timer0init(void)
{
    TMOD=(TMOD&0xF0)|0x02;
    TH0=(256-200);
    TL0=(256-200);
    ET0=1;
    EA=1;
    TR0=1;
}

void timer0(void) interrupt 1
{
    COUNTER++;

    if ((COUNTER==PWM))
    {
        COUNTER=0;
        P1_0=0;
        if (dflg==0)
            PWMH++;
        else
            PWMH--;
    }
    else if (COUNTER==PWMH)
    {
        P1_0=1;
    }
}


void main(void)
{
    dflg=0;
    P1_0=1;
    PWMH=0;
    PWM=60;
    timer0init();
    while (1)
    {
        if (PWMH==PWM)
        {
            PWMH--;
            COUNTER=0;
            dflg=1;
        }
        if ((PWMH==0)&&(dflg==1))
        {
            PWMH=1;
            COUNTER=0;
            dflg=0;
        }

    }
}