Dear Bert, Andy, Richard and Erik,

The module come with 115200 baud by default,
the baud rate can be change to lower speed down to 1200,
BUT
the module should be connected firstly with a computer
to send at command via hyperterminal at least, then
the module can communicate with the microcontroller.

Whenever the main power is fail, the baud rate of the module
set back to 115200 again, therefore if the baudrate AT89c2051
as the controller, then no more setting is needed.

At the moment, I'm still trying all suggestions,
Any way thank you,

Kurnia Brahmana