CCS/TMS320F28335: RXRDY bit is not set when received character.

Tool/software: Code Composer Studio

I imported example_2833xSci_echoback project from controlsuite,  the program works fine, but I found that RXRDY bit in SCIRXST register is not set to "1' in the debug register window when  the program reaching the line which is going to read received char from the SCIRXBUF. The source code is as followings and I put the breakpoint at the second statement. Should the RXRDY bit be '1' at this moment? thanks 

// Wait for inc character
while(SciaRegs.SCIFFRX.bit.RXFFST !=1) { } // wait for XRDY =1 for empty state

// Get character
ReceivedChar = SciaRegs.SCIRXBUF.all;