--++¦

本人初学VHDL时编的比较系统的VHDL源程序 巨实用

library IEEE;
use IEEE.std_logic_1164.all;

entity tobcd is
    port (
        a: in STD_LOGIC_VECTOR (3 downto 0);
        b: out STD_LOGIC_VECTOR (3 downto 0);
        c: out STD_LOGIC_VECTOR (3 downto 0)
    );
end tobcd;

architecture tobcd_arch of tobcd is
begin
     with a select
     b<="0000" when "0000",
     	"0000" when "0001",
     	"0000" when "0010",
     	"0000" when "0011",
     	"0000" when "0100",
     	"0000" when "0101",
     	"0000" when "0110",
     	"0000" when "0111",
    	"0000" when "1000",
     	"0000" when "1001",
     	"0001" when "1010",
     	"0001" when "1011",
     	"0001" when "1100",
     	"0001" when "1101",
     	"0001" when "1110",
     	"0001" when "1111",
     	"0000" when others;	
     	with a select
     c<="0000" when "0000",
     	"0001" when "0001",
     	"0010" when "0010",
     	"0011" when "0011",
     	"0100" when "0100",
     	"0101" when "0101",
     	"0110" when "0110",
     	"0111" when "0111",
    	"1000" when "1000",
     	"1001" when "1001",
     	"0000" when "1010",
     	"0001" when "1011",
     	"0010" when "1100",
     	"0011" when "1101",
     	"0100" when "1110",
     	"0101" when "1111",
     	"0000" when others;
  -- <<enter your statements here>>
end tobcd_arch;