You say you use timer 2 to generate the baudrate. But timer 2 is not "standard" on all versions of the 8052. Maybe the one on the aduc812 differs too much from timer 2 on the original 8052. Why don't you use the "standard" timer 1 instead, so you free the much more powerfull timer 2 for other purposes?

Do you have an oscilloscope? You can verify what is sent if you repeatedly transmit a short message.