Шим COVOX на VHDL

Всем привет! Подскажите реализацию, может кто делал.

Вот простой пример:

Код:

---

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

entity PWM is
  port (
  clk : in std_logic;
  PWM_in : in std_logic_vector (7 downto 0) := "00000000";
  PWM_out : out std_logic
  );
end PWM;

architecture PWM_arch of PWM is
  signal  PWM_Accumulator : std_logic_vector(8 downto 0);
begin
  process(clk, PWM_in)
  begin
    if rising_edge(clk) then     
      PWM_Accumulator  <=  ("0" & PWM_Accumulator(7 downto 0)) + ("0" & PWM_in);
    end if;
  end process;

  PWM_out <= PWM_Accumulator(8);
end PWM_arch;

---

Взято отсюда: http://www.fpga4fun.com/PWM_DAC.html
Manual: http://www.compadre.org/advlabs/bfy/...BFYHandout.pdf

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