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--******************************************************************************
--*                                                                            *
--*      Synchronous Binary 4bits Up-Down Counter without Carry/Borrow         *
--*                                                     Device : XC9536-PC44   *
--*                                                     Author : Seiichi Inoue *
--******************************************************************************

library ieee;                                    -- Library declaration
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity UD_COUNTER1 is
  port ( CLK,CLEAR,LOAD,CE,UP : in std_logic;    -- INPUT and OUTPUT declaration
         DIN : in std_logic_vector(3 downto 0);
         Q : out std_logic_vector(3 downto 0));
  attribute pin_assign : string;                 -- Pin assign
  attribute pin_assign of CLK : signal is "1";
  attribute pin_assign of CLEAR : signal is "2";
  attribute pin_assign of LOAD : signal is "3";
  attribute pin_assign of CE : signal is "4";
  attribute pin_assign of UP : signal is "8";
  attribute pin_assign of DIN : signal is "38,37,36,35";
  attribute pin_assign of Q : signal is "14,13,12,11";
end UD_COUNTER1;

architecture UD_COUNTER_ARCH of UD_COUNTER1 is
signal Q_IN : std_logic_vector(3 downto 0);      -- Internal counter signal
begin
  Q <= Q_IN;                                     -- Set output
  process( CLEAR, CLK, LOAD, CE, UP ) begin
    if CLEAR='1' then                            -- CLEAR = ON ?
       Q_IN <= "0000";                           -- Yes. Counter clear
    elsif CLK='1' and CLK'event then             -- Clock in ?
       if LOAD='1' then                          -- Yes. LOAD = ON ?
          Q_IN <= DIN;                           -- Set Input to Output
       else                                      -- LOAD = OFF
          if CE='1' then                         -- Count Enable ?
             if UP='1' then                      -- Yes. Up count ?
                Q_IN <= Q_IN + '1';              -- Yes. Count-up
             else                                -- Not count-up
                Q_IN <= Q_IN - '1';              -- Count-down
             end if;
          end if;                                -- Not CE = 1
       end if;
    end if;
  end process;
end UD_COUNTER_ARCH;

--******************************************************************************
--*             end of Synchronous Binary 4bits Up-Down Counter                *
--******************************************************************************