int    counter = -22;
int    result = 1;

void timer0handler( void ) interrupt 1 {
       counter --;
       if (counter == -20 )
          counter = 0;
       if (counter == -5 )
          counter -= 10;
       if (counter <-40 )
          counter = 0;
}

void main( void ) {
      Init_Timer;			// timer 1000x/s

      while (1) {
        if (counter == -10)
           result = 5;             // A
        if (counter == -30)
           result = 10;            // B
        if ((counter-result)>0)
           result = 100;           // C
        if ((counter-result)<-400)
           result = 100;       }   // C
  }