conta_updown

-- Contador de década sobe e desce
-- Entradas: clk (clock), reset;
-- Saída: q (Vetor 4 posições tipo BCD)
-- Autores: João Vitor e Marcos Meira
-- 02/08/2017

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

entity conta_updown is
  port (
    clk:in bit;
    reset: in bit;
     sobedesce: in bit;
     carry_out: out bit;
    q: out std_logic_vector(3 downto 0)
    );
end conta_updown;

architecture arquitetura of conta_updown is
begin
    process(clk,reset)
    variable qtemp: std_logic_vector(3 downto 0);
    begin
        if reset='1' then
        qtemp:="0000";

        else
            if clk'event and clk='1' then

                if sobedesce='1' then   ---     QUANDO sobedesce FOR 1
                    if qtemp<9 then     ---
                    qtemp:=qtemp+1;      ---
                    carry_out <= '0';       ---
                    else                        ---     CONTADOR CRESCENTE
                    qtemp:="0000";       ---
                    carry_out <= '1';       ---
                    end if;                 ---
----------------------------------------------------------------
                else                            --- QUANDO sobedesce FOR 0
                    if qtemp>0 then     ---
                    qtemp:=qtemp-1;     ---
                    carry_out <= '0';       ---
                    else                        --- CONTADOR DECRESCENTE
                    qtemp:="1001";          ---
                    carry_out <= '1';       ---
                    end if;                 ---

                end if;
            end if;
        q<=qtemp;
        end if;
    end process;
end arquitetura;