44个vhdl实例 注1： 含有不可综合语句

-- State Machine with Moore and Mealy 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);
        w:              out std_logic;
        y:              out std_logic_vector(1 downto 0));
end mealy1;

architecture archmealy1 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;
                elsif (clk'event and clk='1') then
                        case state is
                                when state0 =>
                                        if id = x"3" then
                                                state <= state1;
                                        else
                                                state <= state0;
                                        end if;
                                when state1 =>
                                        state <= state2;
                                when state2 =>
                                        if id = x"7" then
                                                state <= state3;
                                        else
                                                state <= state2;
                                        end if;
                                when state3 =>
                                        if id < x"7" then 
                                                state <= state0;
                                        elsif id = x"9" then
                                                state <= state4;
                                        else
                                                state <= state3;
                                        end if;
                                when state4 =>
                                        if id = x"b" then
                                                state <= state0;
                                        else
                                                state <= state4;
                                        end if;
                        end case;
                end if;
        end process;

--assign moore state outputs;
y <= "00" when (state=state0) else
     "10" when (state=state1 or state=state3) else
     "11"; 
--assign mealy output;
w <= '0' when (state=state3 and id < x"7") else
     '1';
end archmealy1;