#include <mega8.h>

// Timer 0 overflow interrupt service routine
interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{
if (PORTC.5==0)
{
PORTC.5=1;
PORTC.4=0;
}
else
{
PORTC.5=0;
PORTC.4=1;
}
// Place your code here

}

// Declare your global variables here

void main(void)
{
PORTC.5=0;
PORTC.4=1;
// Declare your local variables here

// Input/Output Ports initialization
// Port B initialization
// Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=Out
// State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=0
PORTB=0x00;
DDRB=0x01;

// Port C initialization
// Func6=In Func5=Out Func4=Out Func3=Out Func2=Out Func1=Out Func0=Out
// State6=T State5=0 State4=0 State3=0 State2=0 State1=0 State0=0
PORTC=0x00;
DDRC=0x3F;

// Port D initialization
// Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In
// State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=T
PORTD=0x00;
DDRD=0x00;

// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: 3,906 kHz
TCCR0=0x04;
TCNT0=0x00;

// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: Timer 1 Stopped
// Mode: Normal top=FFFFh
// OC1A output: Discon.
// OC1B output: Discon.
// Noise Canceler: Off
// Input Capture on Falling Edge
TCCR1A=0x00;
TCCR1B=0x00;
TCNT1H=0x00;
TCNT1L=0x00;
ICR1H=0x00;
ICR1L=0x00;
OCR1AH=0x00;
OCR1AL=0x00;
OCR1BH=0x00;
OCR1BL=0x00;

// Timer/Counter 2 initialization
// Clock source: System Clock
// Clock value: Timer 2 Stopped
// Mode: Normal top=FFh
// OC2 output: Disconnected
ASSR=0x00;
TCCR2=0x00;
TCNT2=0x00;
OCR2=0x00;

// External Interrupt(s) initialization
// INT0: Off
// INT1: Off
MCUCR=0x00;

// Timer(s)/Counter(s) Interrupt(s) initialization
TIMSK=0x01;

// Analog Comparator initialization
// Analog Comparator: Off
// Analog Comparator Input Capture by Timer/Counter 1: Off
ACSR=0x80;
SFIOR=0x00;

// Global enable interrupts
#asm("sei")

while (1)
{
// Place your code here

};
}

Все отлично зашилось через 5 проводков, диод замигал в опщем щастье!
...
// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: 3,906 kHz

#include <mega8.h>
#include <delay.h>


interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{


}


void main(void)
{

PORTD=0x00;
DDRD=0xFF;
TCCR0=0x04;
TCNT0=0x00;
TIMSK=0x01;
ACSR=0x80;
SFIOR=0x00;

#asm("sei")

while (1)
{
PORTD.0=1;
PORTD.1=0;
delay_ms(100);
PORTD.1=1;
PORTD.0=0;
delay_ms(100);
};
}