funct_4.vhd

来自「VHDL子程序集,包括各种例程资料以及源码.」· VHDL 代码 · 共 39 行

--***************************************
--*   1 To 4 Demultiplexer (FUNCTION)   *
--*         Three 1 To 2 DEMUL          *
--*          Filename : FUNCT_4         *
--***************************************

library IEEE;
use IEEE.std_logic_1164.all;

entity FUNCT_4 is
    port (
          DIN: in STD_LOGIC;
          S:   in STD_LOGIC_VECTOR (1 downto 0);
          Y:   out STD_LOGIC_VECTOR (0 to 3)
         );
end FUNCT_4;

architecture FUNCT_4_arch of FUNCT_4 is
signal X: std_logic_vector(0 to 1);

function DEMUL2 (
                 D: std_logic;
                 S: std_logic
                ) return std_logic_vector is
         variable  F: std_logic_vector(0 to 1);
begin
    case S is
         when '0'    => F := D & '0';
         when others => F := '0' & D; 
    end case;
    return F;
end DEMUL2; 
                       
begin
    X         <= DEMUL2 (DIN,S(1));
    Y(0 to 1) <= DEMUL2 (X(0),S(0));
    Y(2 to 3) <= DEMUL2 (X(1),S(0));
end FUNCT_4_arch;