thanks for answer Mr. Kumar, I am trying to look that wave forms with a LOGIC DART of Hewlett Packard, I should see them, becuase I can see the wave forms of P0 & P2, even I can see a wave form of the PSEN & ALE. I am using 11.059 Mhz crystal, the program make continuous transmision of characters. What do y think about this ? I think we are not setting the baud rate, we are not telling to the microcontroller that send that by TXD pin, maybe that's the problem.