Forum: FPGA, VHDL & Verilog rs232 test VHDL

von Martin M. (martin_m19)

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

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.
library IEEE;

entity top is
    Port ( rxd : in  STD_LOGIC;
           txd : out  STD_LOGIC);
end top;

architecture Behavioral of top is


  txd <= rxd;

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?


von Lothar M. (lkmiller) (Moderator)

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Start as close as possible to the computer!
Do you get the characters echoed, when you bridge Pins 2 and 3 on the 
RS232 cable at the computer (without any FPGA or other hardware)?

Your code is fine. Do you also have assinged the ports to pins in a 
constraints file?

von Martin M. (martin_m19)

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It Works!
I resynthesised and programmed to board. and it works.
Not sure what i did the only main thing i did differently was run Putty 
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