decode.vhd

cpld实现的并行数据串行传输收发模块（类曼切斯特码）。最大2M并行码率。

Library IEEE;
USE IEEE.std_logic_1164.all;
USE IEEE.std_logic_unsigned.all;

ENTITY decode IS
	PORT(clr:in std_logic;
	en  :in	 std_logic;
	clk :in  std_logic;
	d	:in  std_logic;
	q	:out std_logic;
	fail:out std_logic;
	ready:out std_logic;   --数据准备好
	clk1x:out std_logic;
	clk2x:out std_logic;
	deco_o:out std_logic;
	jo_o  :out std_logic
	);
END decode;

ARCHITECTURE decode of decode is
SIGNAL clk1,clk2,count_t,den,deco,jo,jo_count:std_logic;
SIGNAL chk_r	:std_logic_vector(3 downto 0);
SIGNAL count_m17:std_logic_vector(4 downto 0);
begin

------------------分频器-------------------
process(clk,en,clr)
begin
	if(clr='1') then
		count_t<='1';
	elsif(clk'event and clk='1')then
		if(count_t='1')then
			count_t<='0';
		elsif(en='1')then
			count_t<='1';
		end if;
	end if;
end process;
clk2<=count_t;
clk1<=not(not(clk and '1'));
clk1x<=clk1;
clk2x<=clk2;

------------------M17---------------------
process(clk2,den,clr)      ---2同步码+16数据+1奇偶+（1空闲）
begin
	if(clr='1') then
		count_m17<="00000";
	elsif(clk2'event and clk2='1')then
		if(count_m17="10000" )then
			count_m17<="00000";
		elsif(den='1')then
			count_m17<=count_m17+'1';
		end if;
	end if;
end process;

-----------------同步码检测器--------------
process(clk1,clk2,en,clr,d)
begin
	if(clr='1' or count_m17="10000")then
		chk_r<="0000";
	elsif(clk1'event and clk1='1')then
		if(en='1')then
			chk_r<=chk_r(2 downto 0)&d;
		end if;
	end if;
	
	if(count_m17="10000" or clr='1')then
		den<='0';
	elsif(clk2'event and clk2='1')then
		if(chk_r="1100")then    --同步成功
			den<='1';
		end if;
	end if;
end process;


----------------解码、奇偶校验-------------
process(clk1,clk2,den,d)
begin
	if(den='1')then
		deco<=not(clk2 xor d);	--解码
	else
		deco<='0';
	end if;
	
	if(clk1'event and clk1='1')then
		if(count_m17<="0111" and den='1')then --奇偶校验
			if(jo_count='1')then	--每隔一个clk1采样一次
				jo_count<='0';
			else
				jo<=jo xor deco;
				jo_count<='1';
			end if;
		else
			jo_count<='0';
		end if;
	end if;
	
	if(clk1'event and clk1='1')then
		if(count_m17<="01111" and den='1')then --选择输出，消毛刺
			q<=deco;
		else
			q<='0';
		end if;
	end if;

	
										 --奇偶校验输出
		if(count_m17 ="10000")then
			fail<= jo xor deco;
		else
			fail<= '0';
		end if;

	
	if(clk1'event and clk1='1')then		--ready信号输出，延迟1clk1
		ready<=den;
	end if;
end process;



deco_o<=deco;
jo_o  <=jo;
end decode;