Subversion Repositories ttl_library

-----------------------------------------------------------------------

-- Bipolar TTL models (VHDL)                                         --

-- David R Brooks                                                    --

-- June, 2016.  Perth, Australia                                     --

-- Compliance: VHDL 2008                                             --

-- Testbench for SN74LS168N: Synchronous bidirectional BCD counter   --

-----------------------------------------------------------------------

library ieee;

    use ieee.std_logic_1164.all;

    use ieee.std_logic_misc.all;

    use ieee.numeric_std.all;

    use work.LSTTL.all;

    use work.TTLPrivate.all;

entity Testbench_168 is     -- Top-level bench

generic(

    StimClk  : std_logic      := '1';

    CheckClk : std_logic      := '1';

    Period   : time           := 100 ns;

    Finish   : time           :=  20 us;

    SevLevel : severity_level := failure

);

end entity;

architecture Test of Testbench_168 is

    signal RS      : std_logic;

    signal CLK     : std_logic;

    signal J,  B   : unsigned(6 downto 0);          -- Test stimuli

    signal D,  E   : std_logic_vector(4 downto 0);  -- Expected & actual results

    signal PE      : std_logic := '1';

    signal CEP     : std_logic := '1';

    signal CET     : std_logic := '1';

    signal UD      : std_logic := '1';

    signal X, Y, Z : std_logic;

    signal W       : std_logic_vector(3 downto 0);

    alias  P       : unsigned(3 downto 0) is B(3 downto 0);

    alias  CP      : std_logic is CLK;

    constant modulus  : natural := 10;

    constant limit    : unsigned(3 downto 0) := to_unsigned(modulus-1, 4);

    constant decade   : boolean := true;

    begin

    CEP <= J(0);

    CET <= J(1);

    X <= W(0) and W(3) and not CET;

    Y <= nor_reduce(W) and not CET;

    Z <= not X when UD = '1' else not Y;

    D <= Z & W;

    process(CP, RS) is     -- Generate control signals

        variable T2, T3 : natural := 0;

    begin

        if    RS = '0' then

            PE <= '0';

        elsif rising_edge(CP) then

            if T2 = 37 then

                PE <= '0';

                T2 := 0;

            else

                PE <= '1';

                T2 := T2 + 1;

            end if;

            if T3 = 41 then

                UD <= not UD;

                T3 := 0;

            else

                T3 := T3 + 1;

            end if;

        end if;

    end process;

    -----------------------------------------------------------------------

    -- Standard testbench components

    -----------------------------------------------------------------------

    TB: TTLBench

    generic map(

        StimClk  => StimClk,

        CheckClk => CheckClk,

        Period   => Period,

        Finish   => Finish,

        SevLevel => SevLevel

    )

    port map(

        J    => J,

        B    => B,

        CLK  => CLK,

        RS   => RS,

        D    => D,

        E    => E

    );

    -----------------------------------------------------------------------

    -- Generate expected results (with zero delays)

    -----------------------------------------------------------------------

    process(CP) is

        variable SW : std_logic_vector(3 downto 0);

        variable R  : unsigned(3 downto 0);

    begin

        if CP'event and CP = '1' then       -- Everything is synchronous

            SW := (PE, CEP, CET, UD);

            case SW is

                when "0000" | "0001" | "0010" | "0011" |

                     "0100" | "0101" | "0110" | "0111"=>              -- Load

                    R := unsigned(P);

                when "1001" =>              -- Count up

                    if decade then

                        case R is

                            when "1001" => R := "0000";

                            when "1011" => R := "0100";

                            when "1101" => R := "0100";

                            when others => R := R + 1;

                        end case;

                    else

                        R := R + 1;

                    end if;

                when "1000" =>              -- Count down

                    if decade then

                        case R is

                            when "0000" => R := "1001";

                            when "1010" => R := "0001";

                            when "1100" => R := "0011";

                            when "1110" => R := "0101";

                            when others => R := R - 1;

                        end case;

                    else

                        R := R - 1;

                    end if;

                when others =>              -- No change

                    null;

            end case;

        end if;

        W <= std_logic_vector(R);

    end process;

    -----------------------------------------------------------------------

    -- Device Under Test...                        

    -----------------------------------------------------------------------

    DUT: SN74LS168N

    port map(

    X_1  => UD,    -- U_D\

    X_2  => CP,    -- CP

    X_3  => B(0),  -- P0

    X_4  => B(1),  -- P1

    X_5  => B(2),  -- P2

    X_6  => B(3),  -- P3

    X_7  => CEP,   -- CEP\

    X_8  => open,  -- GND

    X_9  => PE,    -- PE\

    X_10 => CET,   -- CET\

    X_11 => E(3),  -- Q3

    X_12 => E(2),  -- Q2

    X_13 => E(1),  -- Q1

    X_14 => E(0),  -- Q0

    X_15 => E(4),  -- TC\

    X_16 => open   -- Vcc

);

end architecture Test;