sync.vhd

Xilinx_usb_jtag 下载器原理图及程序

--
--   Copyright (C) 2003 by J. Kearney, Bolton, Massachusetts
--
--   This program is free software; you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation; either version 2 of the License, or
-- (at your option) any later version.
--
--   This program is distributed in the hope that it will be useful, but
-- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
-- for more details.
--
--   You should have received a copy of the GNU General Public License along
-- with this program; if not, write to the Free Software Foundation, Inc.,
-- 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
--

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.numeric_std.ALL;

library unisim;
use unisim.vcomponents.all;

entity Sync is
    Port ( RESET : in std_logic;
	 		  REQ : in std_logic;
           ACK : in std_logic;
           STATUS : buffer std_logic);
end sync;

architecture RTL of sync is

	signal acked : std_logic;

begin

	process (reset, req, status, acked)
	begin
		if (reset = '1') or (acked = '1') then
			status <= '0';
		elsif rising_edge(req) then
			status <= '1';
		end if;
	end process;

	process (req, status, ack)
	begin
		if status = '0' then
			acked <= '0';
		elsif rising_edge(ack) then
			acked <= '1';
		end if;
	end process;


end RTL;