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--Nama file : count2x.fsm
--Deskripsi : counter 2 bit
--Author    : Mas Adit
--Tanggal  : 31 Agustus 2001

entity count2x is
port (
        clk : in bit;
        rst : in bit;
       q : out bit_vector(1 downto 0);
       vdd : in bit;
       vss : in bit
      );
end count2x;

architecture STATE_MACHINE of count2x is

type STATE_TYPE IS (S0, S1, S2, S3);

-- pragma CLOCK clk
-- pragma CURRENT_STATE CURRENT_STATE
-- pragma NEXT_STATE NEXT_STATE

signal CURRENT_STATE, NEXT_STATE: STATE_TYPE;

begin
  process ( CURRENT_STATE, rst )
    begin
      if ( rst = '1' ) then
          NEXT_STATE <= S0;
          q <= "00";
      else
          case CURRENT_STATE IS
             when S0 =>
                q <= "00";
                NEXT_STATE <= S1;
             when S1 =>
                q <= "01";
                NEXT_STATE <= S2;
             when S2 =>
                q <= "10";
                NEXT_STATE <= S3;
             when S3 =>
                q <= "11";
                NEXT_STATE <= S0;
             when OTHERS =>
                assert ( '1' )
                report "Illegal State";

          end case;
      end if;
end process;

process (clk)
  begin
    if ((clk = '1') and not (clk'STABLE)) then
         CURRENT_STATE <= NEXT_STATE;
    end if;
end process;

end STATE_MACHINE;