pwm2xeq.vhd

这个是国外大学的项目代码

------------------------------------------------------------------------
--  pwm2xeq.vhd -- Pulse Width Modulator
------------------------------------------------------------------------
--  Author : Kovacs Laszlo - Attila 
------------------------------------------------------------------------
-- Software version: Xilinx ISE 7.1.04i
--                   WebPack
------------------------------------------------------------------------
-- This Pulse Width Modulator according to the 4 most significant bits 
-- of the data input selects one of the 16 logics (pulse widths),
-- using inverse clock signals, so the pulse modulations does 
-- not have the same length.
------------------------------------------------------------------------

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

entity pwm2xeq is
    Port ( CLK2X : in std_logic;
           CLK   : in std_logic;
           CLK2  : in std_logic;
           CLK4  : in std_logic;
           DO    : out std_logic;
           DI    : in std_logic_vector(7 downto 0));
end pwm2xeq;
architecture Behavioral of pwm2xeq is

begin

    with DI(7 downto 4) select
    DO <= '1'                              when "1111", --16
        CLK2X or CLK or CLK2 or CLK4       when "1110", --15
        CLK2X or CLK or CLK2               when "1101", --14
        CLK2X or CLK or (CLK2 and CLK4)    when "1100", --13
        CLK2X or CLK                       when "1011", --12
        CLK2X or (CLK and (CLK2 or CLK4))  when "1010", --11
        CLK2X or (CLK and CLK2)            when "1001", --10
        CLK2X or (CLK and CLK2 and CLK4)   when "1000", --09
        CLK2X                              when "0111", --08
        CLK2X and (CLK or CLK2 or CLK4)    when "0110", --07
        CLK2X and (CLK or CLK2)            when "0101", --06
        CLK2X and (CLK or (CLK2 and CLK4)) when "0100", --05
        CLK2X and CLK                      when "0011", --04
        CLK2X and CLK and (CLK2 or CLK4)   when "0010", --03
        CLK2X and CLK and CLK2             when "0001", --02
        '0' when others;

end Behavioral;