VHDL: How to index a std logic vector

Discussion in 'Programmer's Corner' started by wantanjung, May 25, 2009.

  1. wantanjung

    wantanjung Thread Starter New Member

    Joined:
    May 24, 2009
    Messages:
    6
    Location:
    Singapore GMT + 8
    Dear guys,

    I need some help programming VHDL.

    I need to break up a 8bit binary data to 2 4-bit data. Below is a glimpse of the code:

    library IEEE;
    use IEEE.STD_LOGIC_1164.ALL;
    use IEEE.STD_LOGIC_ARITH.ALL;
    use IEEE.STD_LOGIC_UNSIGNED.ALL;
    use ieee.numeric_std.all;
    use work.CharLoopController.all;


    entity Sub_prog_test is
    Port ( en,reset,DisplayData,clk : in STD_LOGIC;
    Data: in STD_LOGIC_VECTOR (7 downto 0);
    );
    end Sub_prog_test;

    architecture Behavioral of Sub_prog_test is

    begin

    process (clk,en,reset)

    variable upper_4bit, lower_4bit: std_logic_vector (3 downto 0);

    --------------------Some statement-------------------------
    .....................

    upper_4bit<=Data(7)& Data(6)& Data(5)& Data(4);
    lower_4bit<=Data(3)& Data(2)& Data(1)& Data(0);

    However, when i do this, i get an error: "Wrong index type for Data."

    Please help

    Ridwan
  2. wantanjung

    wantanjung Thread Starter New Member

    Joined:
    May 24, 2009
    Messages:
    6
    Location:
    Singapore GMT + 8
    Hi guys..

    Realised my own mistake. Accidently named 2 variables similarly: 1 is data, other is Data. After changing Data to a new name: DataVar, everything went ok.

    Shucks.. I thought VHDL syntax was case sensitive.

    Best Regards

    Ridwan
  3. u0508933

    u0508933 New Member

    Joined:
    Oct 19, 2009
    Messages:
    1
    Hi,

    i am a final year engineering student and i am seeking your help. I am required to design a Mesh Fabric Reference Design using VHDL programming.

    please refer to the following document.

    http://www.xilinx.com/support/documentation/application_notes/xapp698.pdf

    sample source code is not available for this and i have to design this from scratch. Would you be willing to help me. There will be good incentives. Please reply if interested. Thanks.
  4. ridsudcre

    ridsudcre New Member

    Joined:
    Oct 20, 2009
    Messages:
    1
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