Problem mit ATTiny861A

#define F_CPU 1000000

#include <avr/io.h>

#include <util/delay.h>

// device: ATTiny861A

int main ( void )

{

  DDRA   = 0xFF;    // segments output

  DDRB   = 0xFF;    // all digits output

  for(;;)

  {

  _delay_ms(1);

  PORTA  = 0x00;    // all segments reset

  PORTB  = 0x00;    // all digits reset

  _delay_ms(1);

  PORTA  = 0xFF;    // all segments set

  PORTB  = 0xFF;    // all digits set

  }

}