mealy_4.vhd

来自「VHDL子程序集,包括各种例程资料以及源码.」· VHDL 代码 · 共 97 行

--*********************************
--*  3 Bit Even Parity Generator  * 
--*      Filename : MEALY_4       *
--*********************************
        
library IEEE;
use IEEE.std_logic_1164.all;

entity MEALY_4 is
    port (
          CLK:   in STD_LOGIC;
          RESET: in STD_LOGIC;
          X:     in STD_LOGIC;
          Z:     out STD_LOGIC
         );
end MEALY_4;

architecture MEALY_4_arch of MEALY_4 is
type State is (S6,S5,S4,S3,S2,S1,S0);
signal Present_State: State;
signal Next_State: State;
begin
process (CLK,RESET)

begin
    if RESET ='1' then 
       Present_State <= S0;
    elsif  CLK'event and CLK = '1' then
       Present_State <= Next_State;
    end if;
end process;  

process (X,Present_State)

begin
    case Present_State is
         when S0 =>
            if X ='0' then
               Next_State <= S1;
               Z <= '0';
            else
               Next_State <= S2;
               Z <= '0';
            end if;
         when S1 =>
            if X ='0' then
               Next_State <= S3;
               Z <= '0';
            else
               Next_State <= S4;
               Z <= '0';
            end if;
         when S2 =>
            if X ='0' then
               Next_State <= S4;
               Z <= '0';
            else
               Next_State <= S3;
               Z <= '0';
            end if;
         when S3 =>
            if X ='0' then
               Next_State <= S5;
               Z <= '0';
            else
               Next_State <= S6;
               Z <= '0';
            end if;            
         when S4 =>
            if X ='0' then
               Next_State <= S6;
               Z <= '0';
            else
               Next_State <= S5;
               Z <= '0';
            end if;
         when S5 =>
            if X ='0' then
               Next_State <= S0;
               Z <= '0';
            else
               Next_State <= S0;
               Z <= '0';
            end if;
         when S6 =>
            if X ='0' then
               Next_State <= S0;
               Z <= '1';
            else
               Next_State <= S0;
               Z <= '1';
            end if;
    end case;
end process;

end MEALY_4_arch;