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

-- Bipolar TTL models (VHDL)                                         --

-- David R Brooks                                                    --

-- August, 2016.  Perth, Australia                                   --

-- Compliance: VHDL 2008                                             --

-- Testbench for SN74LS191N: Up/down binary 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_191 is     -- Top-level bench

generic(

    StimClk  : std_logic      := '1';

    CheckClk : std_logic      := '1';

    Period   : time           := 100 ns;

    Finish   : time           :=  15 us;

    SevLevel : severity_level := failure

);

end entity;

architecture Test of Testbench_191 is

    signal JC, BC : unsigned(6 downto 0);           -- Test stimuli

    signal D, E   : std_logic_vector(5 downto 0);   -- Expected & actual results

    signal P      : unsigned(3 downto 0);

    signal CP     : std_logic;

    signal RS, PL : std_logic;

    signal CE, UD : std_logic;

    signal T1,  T2,  T3,  T4, T5,

           T6,  T7,  T8,  T9, T10,

           T11, T12, T13, T14  : std_logic;

    signal Q, QB, X : unsigned(3 downto 0);

    begin

    P  <= JC(6 downto 3);

    CE <= BC(6);

    process(CP) is

    begin

        if rising_edge(CP) then

            PL <= RS and nand_reduce(std_logic_vector(BC(4 downto 0))) after 10 ns, '1' after 80 ns;

            UD <= BC(5);

        end if;

    end process;

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

    -- Standard testbench components

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

    TB: TTLBench

    generic map(

        StimClk  => StimClk,

        CheckClk => CheckClk,

        Period   => Period,

        Finish   => Finish,

        SevLevel => SevLevel

   )

    port map(

        J    => JC,

        B    => BC,

        CLK  => CP,

        RS   => RS,

        D    => D,

        E    => E

   );

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

    -- Generate expected results (with zero delays)

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

    T1   <= not (UD);

    T2   <= not (UD or CE);

    T3   <= not (CE or T1);

    T4   <= T1 and Q(0) and Q(1) and Q(2) and Q(3);

    T5   <= UD and QB(0) and QB(1) and QB(2) and QB(3);

    T6   <= T3 and QB(0);

    T7   <= Q(0) and T2;

    T8   <= T3 and QB(0) and QB(1);

    T9   <= Q(0) and Q(1) and T2;

    T10  <= T3 and QB(0) and QB(1) and QB(2);

    T11  <= Q(0) and Q(1) and Q(2) and T2;

    X(0) <= not (CE);

    X(1) <= T6 or T7;

    X(2) <= T8 or T9;

    X(3) <= T10 or T11;

    T12  <= not (CP);

    T13  <= not (CE);

    T14  <= T4 or T5;

    process(CP, PL) is

    begin

        if PL = '0' then

            Q <= P;

        elsif rising_edge(CP) and (CE = '0') then

            Q <= Q xor X;       -- 'T' flipflops

        end if;

    end process;

    QB  <= not Q;

    D(3 downto 0) <= std_logic_vector(Q(3 downto 0));

    D(4) <=  T14;

    D(5) <= not (T12 and T13 and T14);

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

    -- Device Under Test...                        

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

    DUT: SN74LS191N

    port map(

        X_1  => P(1), --  P1

        X_2  => E(1), --  Q1

        X_3  => E(0), --  Q0

        X_4  => CE,   --  CE\

        X_5  => UD,   --  U\/D

        X_6  => E(2), --  Q2

        X_7  => E(3), --  Q3

        X_8  => open, --  GND

        X_9  => P(3), --  P3

        X_10 => P(2), --  P2

        X_11 => PL,   --  PL\

        X_12 => E(4), --  TC

        X_13 => E(5), --  RC\

        X_14 => CP,   --  CP

        X_15 => P(0), --  P0

        X_16 => open  --  Vcc

   );

end architecture Test;