11.2.3.4.4 N-bit Up Counter with Load, Count Enable, and Asynchronous Reset

The following examples infer an n-bit up counter with load, count enable, and asynchronous reset.

VHDL

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.std_logic_arith.all;
entity counter is
generic (width : integer := n);
port (data : in std_logic_vector (width-1 downto 0);
load, en, clk, rst : in std_logic;
q : out std_logic_vector (width-1 downto 0));
end counter;
architecture behave of counter is
signal count : std_logic_vector (width-1 downto 0);
begin
process(clk, rst)
begin
if rst = '1' then
count <= (others => '0');
elsif (clk'event and clk = '1') then
if load = '1' then
count <= data;
elsif en = '1' then
count <= count + '1';
end if;
end if;
end process;
q <= count;
end behave;