--Robin Gonzalez. código en VHDL de una maquina de estados para un sistema de alarma, implementado en un GAL22v10
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
entity alarm is port (
    clk: in std_logic;
    a: in std_logic_vector(3 downto 0);
    b: in std_logic_vector(3 downto 0);
    ledOn: out std_logic;
    x: out std_logic_vector(1 downto 0));
 attribute pin_numbers of alarm: entity is
    --inputs
    "b(0):6 b(1):5 b(2):4 b(3):3 "
    &
    "a(0):10 a(1):9 a(2):8 a(3):7 "
    --outputs
    &
    "x(0):15 x(1):16 "
    &
    "ledOn:17";
end alarm;

architecture arch_alarm of alarm is
    type states is (state0, state1, state2, state3 );
    signal stado_pres, stado_fut: states;
    --type boolean is (true, false);
    --signal vdd: boolean;
begin

p_estados: process(stado_pres,a,b) begin
    case stado_pres is
                when state0 =>
                    x <= "00";
                    ledOn <= '0';
                    if a = NOT(b) then
                        stado_fut <= state1;
                    else
                        stado_fut <= state0;
                    end if;
                when state1 =>
                    x <= "01";
                    if a = NOT(b) then
                        stado_fut <= state2;
                    else
                        stado_fut <= state0;
                    end if;
                when state2 =>
                    x <= "10";
                    if a = NOT(b) then
                        stado_fut <= state3;
                    else
                        stado_fut <= state0;
                    end if;
                when state3 =>
                    x <= "11";
                    if a = NOT(b) then
                        ledOn <= '1';
                    end if;
                    stado_fut <= state0;
            end case;
    end process p_estados;

    p_reloj: process(clk) begin
        if(clk'event and clk= '1') then
            stado_pres <= stado_fut;
        end if;
    end process p_reloj;
end arch_alarm;