key_detect_tut.vhd

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-------------------------------------------------------------------------------
--! @file         key_detect_tut.vhd
--! @author       Prof. Dr.-Ing. Ferdinand Englberger
--! @version      V3.0.2
--! @date         14.12.2012
--!
--! @brief        Key-Detector
--! @details      The component detects a press of key and
--!               gererates a detection signal for one clock period
--!
--! @par History:
--! @details      V3.0.2 Ferdinand Englberger
--!               - english comments
--! @details      V3.0.1 13.12.2011 Ferdinand Englberger
--!               - Umlaut in comments
--! @details      V3.0.0 25.12.2010 Ferdinand Englberger
--!               - start of development for this component
-------------------------------------------------------------------------------

--! Use Standard Library
LIBRARY ieee; 
--! Use Logic Elements
USE ieee.std_logic_1164.all;
--! Use Conversion Functions
USE ieee.std_logic_arith.all;
--! Use Conversion Functions
USE ieee.std_logic_signed.all;

--! @brief Tutorial-Component Key-Detector
entity key_detect_tut is
  port
  (
    clock      : in  STD_LOGIC; --! Component Clock
    reset_n   : in  STD_LOGIC; --! Component Reset
    key_input  : in  STD_LOGIC; --! Siggnal vom Taster
    key_detect : out STD_LOGIC  --! Detect-Signal for key
  );
end key_detect_tut;

--! @brief Architecture of Key-Detector
--! @details a key is debounced and a detect signal
--!          is generated (1 clock period)
architecture mykeydetect of key_detect_tut is
  
  --! Statedefinition for key detector
  TYPE STATE_TYPE IS (start, newpress, pressed);
  --! State signal for key detector
  SIGNAL STkey: STATE_TYPE;
  
begin  
    --! @brief detect and debounce the press of a key
    --!        at key-input-line. Generate a press detect 
    --!        signal (1 clock period))
    debounce : process (clock, reset_n, key_input)
    begin
       if (reset_n = '0') THEN
         STkey <= start; 
       elsif (rising_edge(clock)) THEN
         case STkey IS
            when start =>
               if(key_input = '0') THEN
                  STkey <= newpress;
               else
                  STkey <= STkey;
               end if;
            when newpress =>
                 STkey <= pressed;
            when pressed =>
               if(key_input = '1') THEN
                  STkey <= start;
               else
                  STkey <= STkey;
               end if;
            when others => STkey <= start;
         end case;
       end if;
    end process;
    
    key_detect <= '1' WHEN STkey = newpress ELSE
                  '0';
end mykeydetect;