#include <REGX51.h>

void main ()
	
	{
while (1)											//continuous loop

{
if(P0_0==0)
P0_0=1;
else
P0_0=0;

if(P0_1==0)
P0_1=1;
else
P0_1=0;

if(P0_2==0)
P0_2=1;
else
P0_2=0;

if(P0_3==0)
P0_3=1;
else
P0_3=0;

}
	}