Problem with rs232 on smartrf04eb

Hi, I am new to zigbee. I am trying to send and recieve data between Hyperterminal and SmartRF04EB. I am using the "Sereial App" program, given with the Zstack as a base. I am able to send data using HalUARTWrite(). But when i try to read data using HalUARTRead(), it reads nothing. Curiously, If some data is already written to hyperterminal using HalUARTWrite(), that much of data can be read!