Contador de 4 bits

library ieee;
use ieee.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;

entity contador is port(
clk,sentido:    in std_logic;
conta:buffer std_logic_vector(3 downto 0)
);
end contador;

architecture archicontador of contador is
begin
process (clk)
begin
    if(clk'event and clk='1') then
    if sentido = '1' then
        conta <= conta - 1;
    else
        conta <= conta + 1;
    end if;
    end if;
end process;
end archicontador;