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--

-- Rotary Control for Spartan 3E Starter Kit

-- Adapted to attach to z80soc by:

--

-- Ronivon C. Costa

-- 2008/05/12

--

-------------------------------------------------------------------------------------------

-- Reference design - Rotary encoder and simple LEDs on Spartan-3E Starter Kit (Revision C)

--

-- Ken Chapman - Xilinx Ltd - November 2005

-- Revised 20th February 2006

--

-- This design demonstrates how to interface to the rotary encoder and simple LEDs.

--    At the start, only one LED is on. 

--    Turning the rotary encoder to the left or right will cause

--    the LED which is on to appear to also move in the corresponding direction.

--    Pressing the rotary encoder will invert all LEDs so that only one is off.

--

-- The design also uses the 50MHz oscillator provided on the board.

--

-- Instructional value

--   Basic VHDL including definition of inputs and outputs.

--   UCF (User Constraints File) constraints to define pin assignments to match board.

--   UCF constraints to apply pull-up and pull-down resistors to input pins.

--   Detecting rotary movement.

--   Synchronous design.

--

------------------------------------------------------------------------------------

--

-- NOTICE:

--

-- Copyright Xilinx, Inc. 2006.   This code may be contain portions patented by other 

-- third parties.  By providing this core as one possible implementation of a standard,

-- Xilinx is making no representation that the provided implementation of this standard 

-- is free from any claims of infringement by any third party.  Xilinx expressly 

-- disclaims any warranty with respect to the adequacy of the implementation, including 

-- but not limited to any warranty or representation that the implementation is free 

-- from claims of any third party.  Furthermore, Xilinx is providing this core as a 

-- courtesy to you and suggests that you contact all third parties to obtain the 

-- necessary rights to use this implementation.

--

------------------------------------------------------------------------------------

--

-- Library declarations

--

-- Standard IEEE libraries

--

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY ROT_CTRL IS

        PORT (

                CLOCK                           : IN STD_LOGIC;

                ROT_A                           : IN STD_LOGIC;

                ROT_B                           : IN STD_LOGIC;

                DIRECTION               : OUT   STD_LOGIC_VECTOR(1 DOWNTO 0));

END ROT_CTRL;

ARCHITECTURE RTL OF ROT_CTRL IS

SIGNAL rotary_in                        : std_logic_vector(1 downto 0);

SIGNAL rotary_in_a              : std_logic;

SIGNAL rotary_in_b              : std_logic;

SIGNAL rotary_q1                        : std_logic;

SIGNAL rotary_q2                        : std_logic;

SIGNAL delay_rotary_q1  : std_logic;

SIGNAL rotary_event             : std_logic;

SIGNAL rotary_left              : std_logic;

SIGNAL counter                          : std_logic_vector(21 downto 0);

BEGIN

--

-- Define direction based on rotary movement, and return to processor

--

  return_dir: process(CLOCK)

  begin

                if CLOCK'event and CLOCK = '1' then

                        if rotary_event='1' then

                                if rotary_left='1' then

                                        DIRECTION <= "10"; -- Rotating to the left

                                        counter <= "0000000000000000000000";

                                else

                                        DIRECTION <= "01"; -- Rotating to the right

                                        counter <= "0000000000000000000000";

                                end if;

                        else

                                if counter = "1111111111111111111111" then

                                        DIRECTION <= "00";

                                        counter <= "0000000000000000000000";

                                else

                                        counter <= counter + 1;

                                end if;

                        end if;

                end if;

        end process;

  ----------------------------------------------------------------------------------------------------------------------------------

  -- Interface to rotary encoder.

  -- Detection of movement and direction.

  ----------------------------------------------------------------------------------------------------------------------------------

  --

  -- The rotary switch contacts are filtered using their offset (one-hot) style to  

  -- clean them. Circuit concept by Peter Alfke.

  -- Note that the clock rate is fast compared with the switch rate.

--

-- The rising edges of 'rotary_q1' indicate that a rotation has occurred and the 

-- state of 'rotary_q2' at that time will indicate the direction. 

--

rotary_direction: process(CLOCK)

begin

        if CLOCK'event and CLOCK='1' then

                delay_rotary_q1 <= rotary_q1;

                if rotary_q1='1' and delay_rotary_q1='0' then

                        rotary_event <= '1';

                        rotary_left <= rotary_q2;

                else

                        rotary_event <= '0';

                        rotary_left <= rotary_left;

                end if;

        end if;

end process;

rotary_filter: process(CLOCK)

begin

        if CLOCK'event and CLOCK='1' then

      --Synchronise inputs to clock domain using flip-flops in input/output blocks.             

                rotary_in_a <= ROT_A;

                rotary_in_b <= ROT_B;

                rotary_in <= rotary_in_a & rotary_in_b;

                case rotary_in is

                        when "00" =>

                                rotary_q1 <= '0';

                                rotary_q2 <= rotary_q2;

                        when "01" =>

                                rotary_q1 <= rotary_q1;

                                rotary_q2 <= '0';

                        when "10" =>

                                rotary_q1 <= rotary_q1;

                                rotary_q2 <= '1';

                        when "11" =>

                                rotary_q1 <= '1';

                                rotary_q2 <= rotary_q2;

                        when others =>

                                rotary_q1 <= rotary_q1;

                                rotary_q2 <= rotary_q2;

                end case;

        end if;

end process;

end;