Debounce State Machine

gistfile1.txt

----------------------------------------------------------------------------------
-- Fredrik Brosser
-- Push-Button debouncer
-- EDA234, Group 2
--
-- FILE
-- TempModule.vhd
-- Last Updated: 2011-11-22
--
-- VERSION
-- Hardware ("production") v1.0
--
-- HARDWARE
-- Target Device: XC9572XL
-- I/O Pins Used:
-- Macrocells Used:
-- Product Terms Used:
--
-- DESCRIPTION
-- Debouncing a single input signal
--
----------------------------------------------------------------------------------

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;

Entity debounce is
    port( clk    : in  std_logic;
          rstInt    : in  std_logic;
          btnIn  : in  std_logic;
          btnOut : buffer std_logic
    );
end debounce;

Architecture debounce_bhv of debounce is
  
  type stateType is (s0, s1, s2, s3);
  signal state : stateType;
  signal nextState : stateType;
  
  begin
  
  SyncP : process(clk, rstInt)
  begin
    if(rstInt = '1') then 
      state <= s0;
    elsif(clk'Event and clk = '1') then
      state <= nextState;
    end if;
  end process;
  
  CombP : process(state, btnIn)
  begin
    nextState <= state;
    case state is
      when s0 =>
        if(btnIn = btnOut) then
          nextState <= s1;
        end if;
      when s1 =>
        if(btnIn = btnOut) then
          nextState <= s2;
        end if;
      when s2 =>
        if(btnIn = btnOut) then
          nextState <= s3;
        end if;
      when s3 =>
        nextState <= s0;
        if(btnIn = btnOut) then
          btnOut <= not(btnIn);
        end if;
    end case;
  end process; 
  
end debounce_bhv;