Converting integer to std_logic_vector

Discussion in 'VHDL' started by Rockerboy, Dec 6, 2007.

  1. Rockerboy

    Rockerboy Guest

    Hi,

    I am new to VHDL. I want to convert an integer to std_logic_vector of
    length 32. Is there any in-built function in VHDL for this?

    I am doing the following includes:

    library ieee;
    use ieee.std_logic_1164.all;
    use ieee.std_logic_arith.all;
    use ieee.std_logic_unsigned.all;

    Thanks,
    Abhishek
     
    Rockerboy, Dec 6, 2007
    #1
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  2. Rockerboy

    Rockerboy Guest

    Moments after I posted, I found conv_std_logic_vector is the right
    function
     
    Rockerboy, Dec 6, 2007
    #2
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  3. Rockerboy

    KJ Guest

    Actually you shouldn't use std_logic_arith. It's not an IEEE standard, it's
    just something that an early VHDL supplier came up with...it has some
    issues.

    What you should use instead is ieee.numeric_std. In that package are
    to_unsigned() and to_signed() functions that convert integers into the
    appropriate representations. unsigned and signed can then be simply
    converted to std_logic_vector.

    Usage example:
    use ieee.numeric_std.all;
    .....
    my_slv <= std_logic_vector(to_unsigned(my_integer, my_slv'length)); -- if
    my_integer is actually 'natural'
    my_slv <= std_logic_vector(to_signed(my_integer, my_slv'length)); -- if
    my_integer could be negative

    KJ
     
    KJ, Dec 6, 2007
    #3
  4. Rockerboy

    tigerx Guest

    Hi Abhishek,

    there is an inbuilt function in VHDL to convert interger to
    logic_vector.

    In declaration do like this.

    signal temp_integer: integer;
    signal temp: std_logic_vector(31 downto 0);

    Here how you can convert

    temp <= conv_std_logic_vector(temp_integer,32);


    Enjoy!!!
     
    tigerx, Dec 7, 2007
    #4
  5. Rockerboy

    Dave Guest

    No, really, use to_unsigned from numeric_std, and cast to
    std_logic_vector like KJ says. It is the IEEE standard library for
    signed and unsigned types. Especially when you're learning the
    language, you want to learn to do things the right way, and build good
    coding habits.

    Changing the world, one engineering student at a time...
     
    Dave, Dec 7, 2007
    #5
  6. Rockerboy

    Andy Guest

    The conv_std_logic() function is not "inbuilt" in vhdl. It is a
    function in a package that, while residing in the IEEE library in most
    tools, is not an official part of the language standard or any IEEE
    standard package. It was put there, in violation of the IEEE standard,
    by synopsys, and everyone else has followed suit, to maintain
    compatibility with synopsys.

    The IEEE standard way to use arithmetic with vectors is to cast them
    to numeric_std.signed or numeric_std.unsigned, as appropriate for the
    values you are trying to use. The IEEE standard numeric_std package
    includes conversions to and from signed/unsigned and integer.

    Andy
     
    Andy, Dec 10, 2007
    #6
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