int i;

void Timer0Overflow_ISR() org IVT_ADDR_TIMER0_OVF {
    TCNT0=248;
if(++i==10)
   {
      i=0;
    if(PORTB.B6==0)
       {
        PORTB.B6=1;
        PORTB.B7=0;
       }
     else
       {
        PORTB.B6=0;
        PORTB.B7=1;
       }

   }


}

void main() {

  DDRB   =  0xFF;               // set PORTB as output
  PORTB  =  0;                  // clear PORTB
  
  SREG_I_bit = 1;               // Interrupt enable


  TOIE0_bit  = 1;               // Timer0 overflow interrupt enable     TIMSK=0x01;
  TCCR0  = 5;                   // Start timer with 1024 prescaler

  while (1)                     // Endless loop, port is changed inside Interrupt Service Routine (ISR)
    ;
}