#include <avr/io.h>
#include <util/delay.h>

int main()
{
  // set pin pb7 as output
  DDRB = 0x80; // 0b 1000 0000
  
  while(1)
  {
    // set pin pb7 to high
    PORTB = 0x80; // 0b 0000 0000

    // wait 100ms
    _delay_ms(100);

    // set all pins of port b low
    PORTB = 0x00; // 0b 0000 0000

    // wait 100ms
    _delay_ms(100);
  }
}