I ask about serial tx ,rx in mbed controller

it's right to connect my controller directly to my serial port -15 volt and 15 volt or i should use IC max232

to change their level voltages

You will need a MAX232 or similar to go to a standard serial port. The only time you don't is when interfacing to chips and modules that have "TTL level" serial RX and TX (such as many GPS modules).

Hello Mohamed

I assume you have an USB port on the computer, as you'd need that to program the mbed.
You could use the USB cable connected to the mbed as a serial port, if you install drivers.

Drivers for windows

Here's how to connect to that serial port on the mbed: SerialPC

Regards,
Lerche

A voltage level conversion circuit or http://en.wikipedia.org/wiki/MAX232  IC is required to connect mbed to a real RS-232 serial port. The serial port on a PC uses RS-232 voltage levels +/-3 to +/-15V (i.e., not TTL 0-5V logic levels). This one from http://www.sparkfun.com/commerce/product_info.php?products_id=449  comes with the conversion circuit on a breakout board with the typical DB9 serial connector. It also has LEDs that indicate serial data flow.  You have to solder header pins on it. See last section of http://mbed.org/cookbook/Serial-Interrupts for more info.