Contador

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
use work.std_arith.all;

entity contador is
port(clk, reset, ud: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 ud = '1' then
conta <= conta + 1;
if (conta ="1001") then
conta <= "0000";
end if;
end if;

if ud='0' then
conta <= conta -1;
if (conta = "0000") then
conta <= "1001";
end if;
end if;
end if;
end process;
end archicontador;