44个vhdl实例 注1： 含有不可综合语句

-- Mealy State Machine with Registered Outputs
-- dowload from: www.fpga.com.cn & www.pld.com.cn


library ieee;
use ieee.std_logic_1164.all;

entity mealy1 is port(
        clk, rst:       in std_logic;
        id:             in std_logic_vector(3 downto 0);
        y:              out std_logic_vector(1 downto 0));
end mealy1;

architecture archmealy of mealy1 is
        type states is (state0, state1, state2, state3, state4);
        signal state: states;
begin
moore: process (clk, rst) 
        begin
                if rst='1' then 
                        state <= state0;
                        y <= "00";
                elsif (clk'event and clk='1') then
                        case state is
                                when state0 =>
                                        if id = x"3" then
                                                state <= state1;
                                                y <= "10";
                                        else
                                                state <= state0;
                                                y <= "00";
                                        end if;
                                when state1 =>
                                        state <= state2;
                                        y <= "11";
                                when state2 =>
                                        if id = x"7" then
                                                state <= state3;
                                                y <= "10";
                                        else
                                                state <= state2;
                                                y <= "11";
                                        end if;
                                when state3 =>
                                        if id < x"7" then 
                                                state <= state0;
                                                y <= "00";
                                        elsif id = x"9" then
                                                state <= state4;
                                                y <= "11";
                                        else
                                                state <= state3;
                                                y <= "10";
                                        end if;
                                when state4 =>
                                        if id = x"b" then
                                                state <= state0;
                                                y <= "00";
                                        else
                                                state <= state4;
                                                y <= "11";
                                        end if;
                        end case;
                end if;
        end process;

end archmealy;