XBee pro 900HP development kit

Hello everyone,

I am a newbee to XBee Pro 900HP development kit. I can get communication between two modules by using X-CTU via USB connection to PCs, However, if I use serial port to connect development kit (PIN2-Dout, PIN3-DIN, PIN10-GND connected to my serial port on PC and power board via external power supply), the X-CTU can not communicate with module. I tested the signal on relative pins such as DOUT and DIN, the direction is correct but the voltage level looks odd. It can not reach 0 volt when it is low.
So my question is, is that correct way I did to get communication with XBee via serial port? Did I do something silly so it not working?

Thanks for your help and time.

Kind Regards

The development board you are mounting the radio module on acts s a level shifter and a voltage regulator via the USB port. All other test points only provide direct access to the 3.3V CMOS level pins of the XBee module.