移位寄存器的VHDL描述

8位移位寄存器

LIBRARY ieee;

USE ieee.std_logic_1164.all;

ENTITY shifter IS

PORT (

data_in: IN STD_LOGIC_VECTOR(7 DOWNTO 0);--輸入的數據

 n: IN STD_LOGIC_VECTOR(2 DOWNTO 0);--移位的數量

dir: IN STD_LOGIC--移動的方向 0:左  1:右

kind: IN STD_LOGIC_VECTOR(1 DOWNTO 0)；--移動類型  00:算術移  01:邏輯移  10:循環移

clock: IN BIT；--手動時鐘PULSE

data_out: OUT STD_LOGIC_VECTOR(7 DOWNTO 0)--移位的結果

    );

END shifter;ARCHITECTURE behav of shifter IS

BEGIN

PROCESS (data_in, n, dir, kind)  

VARIABLE x,y : STD_LOGIC_VECTOR(7 DOWNTO 0);

VARIABLE ctrl0,ctrl1,ctrl2 : STD_LOGIC_VECTOR (3 DOWNTO 0);

BEGIN

IF (clock'EVENT AND clock = '1')THEN--產生控制向量ctrl

ctrl0 := n(0) & dir & kind(1) & kind(0);

ctrl1 := n(1) & dir & kind(1) & kind(0);

ctrl2 := n(2) & dir & kind(1) & kind(0);

ctrl2 := n(2) & dir & kind(1) & kind(0);

CASE ctrl0 IS

WHEN "0000" | "0001" | "0010" | "0100" | "0101" | "0110"  =>  x := data_in;  --n=0時不移動

WHEN "1000" => x := data_in(6 DOWNTO 0) & data_in(0);--算術左移1位 

WHEN "1001" => x := data_in(6 DOWNTO 0) & '0';--邏輯左移1位 

WHEN "1010" => x := data_in(6 DOWNTO 0) & data_in(7); --循環左移1位

WHEN "1100" => x := data_in(7) & data_in(7 DOWNTO 1);-算術右移1位 

WHEN "1101" => x := '0' & data_in(7 DOWNTO 1);--邏輯右移1位 

WHEN "1110" => x := data_in(0) & data_in(7 DOWNTO 1);--循環右移1位

WHEN others => null;

END CASE;

CASE ctrl1 IS

WHEN "0000" | "0001" | "0010" | "0100" | "0101" | "0110"  =>  y := x;        --n=0時不移動

WHEN "1000" => y := x(5 DOWNTO 0) & x(0) & x(0);--算術左移2位 

WHEN "1001" => y := x(5 DOWNTO 0) & "00";--邏輯左移2位 

WHEN "1010" => y := x(5 DOWNTO 0) & x(7 DOWNTO 6);--循環左移2位

WHEN "1100" => y := x(7) & x(7) & x(7 DOWNTO 2);--算術右移2位 

WHEN "1101" => y := "00" & x(7 DOWNTO 2);--邏輯右移2位 

WHEN "1110" => y := x(1 DOWNTO 0) & x(7 DOWNTO 2);--循環右移2位

WHEN others => null;

END CASE;CASE ctrl2 IS

WHEN "0000" | "0001" | "0010" | "0100" | "0101" | "0110"  => data_out <= y;  --n=0時不移動

WHEN "1000" => data_out <= y(3 DOWNTO 0) & y(0) & y(0) & y(0) & y(0); --算術左移4位 

WHEN "1001" => data_out <= y(3 DOWNTO 0) & "0000"; --邏輯左移4位 

WHEN "1010" | "1110" => data_out <= y(3 DOWNTO 0) & y(7 DOWNTO 4);--循環左(右)移4位

WHEN "1100" => data_out <= y(7) & y(7) & y(7) & y(7) & y(7 DOWNTO 4);--算術右移4位 

WHEN "1101" => data_out <= "0000" & y(7 DOWNTO 4);--邏輯右移4位          

WHEN others => null;

END CASE;       

END IF;

END PROCESS;

END behav;