ppm_de.txt

ppm是通信类系统比较重要的前段部件

library ieee;
	use ieee.std_logic_1164.all;
	use ieee.std_logic_unsigned.all;

entity ppm_d is
	port(clk,rst,din:in std_logic;
	d_en,f_en:out std_logic;
	dout:out std_logic_vector(7 downto 0));
end;	

architecture rtl of ppm_d is
	type state is ( s0,s2,s1,s3,s4,s5);
	signal next_state :state;
	signal now_state :state;	
	signal clk0:std_logic;
	signal q:integer range 0 to 7;
	signal counter,counter_1:std_logic_vector(2 downto 0);
	signal reg,temp:std_logic_vector(7 downto 0);


begin

	process(clk,rst)
	begin
		if rst='1' 	then
			counter<="000";
			clk0<='0';
		elsif clk'event and clk='1'	then
			
			if counter/="111"	then
				counter<=counter+1;
			else
				counter<="000";
				clk0<=not clk0;
			end if;
		end if;
	end process;

	process(din,clk0,temp,rst,now_state)
	begin
		if rst='1'	then
			reg<="00000000";
			d_en<='0';f_en<='0';
			next_state<=s0;
		elsif clk0'event and clk0='1'	then
			now_state<=next_state;
			reg<=reg(6 downto 0)&din;
			f_en<='0';d_en<='0';

			case now_state is
				when s0 =>
					if reg="01111011"	then
						next_state<=s1;
						q<=0;counter_1<="000";
					end if;
				when s1 =>
					if counter_1="011"		then
						if reg(3 downto 0)="1101"	then
							next_state<=s0;
							f_en<='1';
							dout<=temp;
						end if;
					elsif counter_1="111"		then
						if reg="10111111"	then
							next_state<=s2;
						elsif reg="11101111"	then
							next_state<=s3;
						elsif reg="11111011"	then
							next_state<=s4;
						elsif reg="11111110"	then
							next_state<=s5;
						end if;					
						counter_1<="000";
						d_en<='1';
					else
						counter_1<=counter_1+"001";
					end if;
				when s2 => 
					next_state<= s1;q<=q+2;
					temp(q)<='0';temp(q+1)<='0';
				when s3 =>
					next_state<= s1;q<=q+2;
					temp(q)<='1';temp(q+1)<='0';
				when s4 => 
					next_state<= s1;q<=q+2;
					temp(q)<='0';temp(q+1)<='1';
				when s5 =>
					next_state<= s1;q<=q+2;				
					temp(q)<='1';temp(q+1)<='1';
				when others => next_state<=s0;
			end case;
		end if;
	end process;
end;