flip - flop circuit

This circuit represent flip - flop circuit. This circuit showed in proteus simulation.
LED will be light with delay configuration. LED will do changing from ON to OFF or OFF to ON.
LED will be light if it is given low voltage (logic 0). In this opportunity, i used C program..
This is listing program,
//----------------------------
//led flip - flop
//by fais_tech
//----------------------------

#include
#include
void main(void)
{
char a,b;
a=0x0f;
b=0xf0;
DDRA=0xff;

while(1)
{
PORTA=a;
delay_ms(500);
PORTA=b;
delay_ms(500);
}
}