Dear Klaus,
You are right in all way, its great too. But have you seen the data sheet? They have used level shifter IC on board. This is the reason why I am applying 5V to microcontroller and 3.3 V to the wifi Board. Hope you have understood. But still am not able to find why, I am not getting the correct reply. I am getting reply as "System Power on \r\n-Command mode- MACaddress-00000443d4rf" for all data send even for wrong AT command send. Even if I have send "123456"CR , the same result.