rs232 test VHDL

Using Digilent Nexys 2 board which has a rs232 port (uses the Spartan 3E 
fpga).

Trying to test the rs232, i have a usb to rs232 cable and i use Putty 
which all seems to  be working ok. So i wrote this for the FPGA to loop 
back RX and TX so the fpga would just echo back what ever data it got.

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library IEEE;

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use IEEE.STD_LOGIC_1164.ALL;

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entity top is

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    Port ( rxd : in  STD_LOGIC;

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           txd : out  STD_LOGIC);

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end top;

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architecture Behavioral of top is

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begin

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  txd <= rxd;

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end Behavioral;

Unfortunately once put on the fpga i can't write anything in the 
terminal which i think is because the fpga is not echoing back the data.

Can anyone see the problem here? Or have a better way to test the rs232?

Thanks.