rotary_counter.vhd

it is a rotatry counter .it will work on spartan 3 xilini devices.

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


entity Rotary_Counter is
	--	Generic (	bits : Integer := 12);  --8
    Port 		( CLK : in  STD_LOGIC;
							ROT_A : in  STD_LOGIC;
							ROT_B : in  STD_LOGIC;
							ROT_CENTER : in STD_LOGIC;
							COUNTER : out  STD_LOGIC_VECTOR (11 downto 0));
end Rotary_Counter;

architecture Behavioral of Rotary_Counter is

	component Monoflop	port (	
			Clk			: IN	std_logic;	 	-- System Clock
			Trigger		: IN	std_logic;	
			PULSOUT		: OUT std_logic );
	end component;


signal rst    : STD_LOGIC;
signal sROT_A : STD_LOGIC;
signal sROT_B : STD_LOGIC;

signal sCount : STD_LOGIC_VECTOR (11 downto 0);
signal sROT   : STD_LOGIC_VECTOR (1 downto 0);

type 		tstates is (state0, state1, state2, state3, state4, state5, state6);
signal 	State:	tstates;


begin ------------------------

rst <= ROT_CENTER;


MF1: 	Monoflop port map (Clk => CLK,	Trigger => ROT_A, PULSOUT => sROT_A);
MF2: 	Monoflop port map (Clk => CLK,	Trigger => ROT_B, PULSOUT => sROT_B);

sROT(0) <= ROT_A or sROT_A;
sROT(1) <= ROT_B or sROT_B;

process (clk, rst)
begin
	if rst='1' then
		state <= state0;
		sCount<= (others => '0');
	elsif rising_edge(Clk) then
		case state is
			
			when state0 =>
				if sROt = "11" then
					state <= state0;
				elsif sROt = "01" then
					state <= state1;
				else
					state <= state4;
				end if;
			
			when state1 =>
				if sROt = "01" then
					state <= state1;
				elsif sROt = "00" then	
					state <= state2;
				else
					state <= state0;
				end if;
			
			when state2 =>
				if sROt = "00" then
					state <= state2;			
				elsif sROt = "10" then
					state <= state3;
				else
					state <= state1;
				end if;				
			
			when state3 =>
				if sROt = "10" then
					state <= state3;			
				elsif sROt = "11" then
					state <= state0;
					sCount <= sCount + 1;
				else
					state <= state2;
				end if;	

			when state4 =>
				if sROt = "10" then
					state <= state4;			
				elsif sROt = "00" then
					state <= state5;
				else
					state <= state0;
				end if;				
			
			when state5 =>
				if sROt = "00" then
					state <= state5;			
				elsif sROt = "01" then
					state <= state6;
				else
					state <= state4;
				end if;				
			
			when state6 =>
				if sROt = "01" then
					state <= state6;			
				elsif sROt = "11" then
					state <= state0;
					sCount <= sCount - 1;
				else
					state <= state5;
				end if;	
		
			when others => 	state <= state0;

		
		end case;
	end if;
end process;

COUNTER <= sCount;


end Behavioral;