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Help with VHDL

  1. Mar 8, 2005 #1
    I'm having trouble with the following VHDL code:

    Code (Text):

    library IEEE;
    use IEEE.STD_LOGIC_1164.ALL;
    use IEEE.STD_LOGIC_ARITH.ALL;
    use IEEE.STD_LOGIC_UNSIGNED.ALL;

    entity circuit is
        port (a, b, c: in std_logic;
            f1, f2, f3, f4, f5, f6: out std_logic);
    end circuit;

    architecture Structural of circuit is
        component NOT1
            port(in1, in2, in3, in4: in std_logic;
                out1, out2, out3, out4: out std_logic);
        end component;

        component AND1
            port(in1, in2, in3, in4, in5, in6, in7, in8: in std_logic;
                out1, out2, out3, out4: out std_logic);
        end component;
       
        component OR1
            port(in1, in2, in3, in4, in5, in6, in7, in8: in std_logic;
                out1, out2, out3, out4: out std_logic);
        end component;     
       
        signal anot, bnot, cnot, or3, or8, or11, and8, or6, and6 : std_logic;
    begin
    G0: NOT1    port map (in1 => a, out1 => anot, in2 => b, out2 => bnot, in3 => or3, out3 => f1, in4 => or3, out4 => f4);
    G1: AND1    port map (in1 => c, in2 => or11, out1 = f3, in3 => a, in4 => bnot, out2 => and8, in5 => a, in6 => or6, out3 => f2, in7 => anot, in8 => b, out4 => and6);                       
    G2: OR1     port map(in1 => and8, in2 => and6, out1 = or11, in3 => bnot, in4 => c, out2 => or8, in5 => anot, in6 => bnot, out3 => or3, in7 => bnot, in8 => c, out4 => or6);
    end Structural;
     
    The compiler says that 'out1' is an undefined symbol in line 30 (G1). I have each gate defined separately, and all port definitions match between the gates and the whole circuit. The individual gates run with no problems, so I don't understand why the program chokes when I try to string them together. Renaming the outputs in G1 and the AND gate have no effect. I'd appreciate any pointers on where I'm going wrong. Everything's fine when I comment out G1 and G2.
     
  2. jcsd
  3. Mar 20, 2005 #2
    Sorry, but I've been preoccupied for the last couple of weeks, and didn't see this. I'm sure you've figured it out by now, but your oversight was a simple typographical one. In your code:

    begin
    G0: NOT1 port map (in1 => a, out1 => anot, in2 => b, out2 => bnot, in3 => or3, out3 => f1, in4 => or3, out4 => f4);
    G1: AND1 port map (in1 => c, in2 => or11, out1 = f3, in3 => a, in4 => bnot, out2 => and8, in5 => a, in6 => or6, out3 => f2, in7 => anot, in8 => b, out4 => and6);
    G2: OR1 port map(in1 => and8, in2 => and6, out1 = or11, in3 => bnot, in4 => c, out2 => or8, in5 => anot, in6 => bnot, out3 => or3, in7 => bnot, in8 => c, out4 => or6);
    end Structural;

    You have a couple of simple of instantiation errors. You might try a couple of tricks to make it a bit easier, especially if you use particular components over and over. There is a different way to assign input signals, using the "port map" construct, than with the {=>} construct. This is to put the signals into the "port map" construct in the order in which they were originally assigned, simply separated by commas. Thus the trick is to simply copy the original "port" statement, paste it into a backup area (say on a Notepad screen), and there remove all but the original port representations and their commas. Then everytime that component is used, copy the part in parentheses back into the "port map" construct, and overlay each input port representation with the name of the signal that goes there.

    Thus, as an example, if we take the device "AND1" and copy it and paste, we get:

    port(in1, in2, in3, in4, in5, in6, in7, in8: in std_logic;
    out1, out2, out3, out4: out std_logic);


    Removing that not needed, we have:

    (in1, in2, in3, in4, in5, in6, in7, in8, out1, out2, out3, out4)
    Then, when we replace the port names with the signals to them, in the "port map" statement, we get:

    G1: AND1 port map(in1, in2, in3, in4, in5, in6, in7, in8, out1, out2, out3, out4);

    which becomes:

    G1: AND1 port map(c, or11, a, bnot, a, or6, anot, b, f3, and8, f2, and6);

    Note that, all signals must be in the correct order.
     
  4. Apr 3, 2005 #3
    Yup, I got it. Thanks for the help!
     
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