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44个vhdl实例 注1： 含有不可综合语句

-- Moore State Machine with explicit state encoding
-- dowload from: www.fpga.com.cn & www.pld.com.cn

library ieee;
use ieee.std_logic_1164.all;

entity moore2 is port(
        clk, rst:       in std_logic;
        id:             in std_logic_vector(3 downto 0);
        y:              out std_logic_vector(1 downto 0));
end moore2;

architecture archmoore2 of moore2 is
        signal state: std_logic_vector(2 downto 0);
-- State assignment is such that 2 LSBs are outputs
constant state0: std_logic_vector(2 downto 0) := "000";
constant state1: std_logic_vector(2 downto 0) := "010";
constant state2: std_logic_vector(2 downto 0) := "011";
constant state3: std_logic_vector(2 downto 0) := "110";
constant state4: std_logic_vector(2 downto 0) := "111";
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;
                                when others =>
                                        state <= state0;
                        end case;
                end if;
        end process;

--assign state outputs (equal to state std_logics)

y <= state(1 downto 0);
end archmoore2;