Subject: Digital System Design

Topic: Design of Sequential circuits using VHDL

Difficulty: High

VHDL Code for 4-Bit Down-Counter:

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity vhdl_binary_counter is

port(C, CLR : in std_logic;

Q : out std_logic_vector(3 downto 0));

end vhdl_binary_counter;

architecture bhv of vhdl_binary_counter is

signal tmp: std_logic_vector(3 downto 0);

begin

process (C, CLR)

begin

if (CLR=’1′) then

tmp <= "1111";

elsif (C’event and C=’1′) then

tmp <= tmp - 1;

end if;

end process;

Q <= tmp;

end bhv;