小弟想设计一个16-4编码器。单独的16-3编码器是没有问题的，16-4在调用底层原件端口映射时出现问题了。请大神分析。
1.16-3编码器
--3-8优先编码器
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
--端口定义
entity sn74ls148 is
port(i:in std_logic_vector(7 downto 0);
  ys:out std_logic;
  yex:out std_logic;
  q:out std_logic_vector(2 downto 0);
  s:in std_logic);
end entity;
--结构体描述
architecture behave of sn74ls148 is
begin
   ys<=not( not(s) and i(0) and i(1) and i(2) and i(3) and  i(4) and  i(5) and i(6) and i(7) );
   yex<=(s or (i(0) and i(1) and i(2) and i(3) and i(4) and i(5)  and i(6) and i(7) ));
process(s,i)
begin
if (s='0') then
  if (i(7)='0') then
  q<="111";
  elsif (i(6)='0') then
  q<="110";
  elsif (i(5)='0') then
  q<="101";
  elsif (i(4)='0') then
  q<="100";
  elsif (i(3)='0') then
  q<="011";
  elsif (i(2)='0') then
  q<="010";
  elsif (i(1)='0') then
  q<="001";
  elsif (i(0)='0') then
  q<="000";
  else
  q<="XXX";
end if;
end if;
end process;
end behave;
2.16-4编码器
--16-4优先编码器
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
--端口定义
entity coder16_4 is
port(data_in:in std_logic_vector(15 downto 0);
  data_out:out std_logic_vector(3 downto 0);
  ys16_4:out std_logic;
  yex16_4:out std_logic
  );
end entity;
--结构体描述
architecture rtl of coder16_4 is
--此处为了和端口映射连接，定义了一些信号，有些糊涂
signal ys_temp:std_logic;
signal yex_temp:std_logic;
signal ys_temp1:std_logic:='0';
signal ys_temp2:std_logic;
signal yex_temp1:std_logic;
signal yex_temp2:std_logic;
signal b,c:std_logic_vector(7 downto 0);
signal d,e:std_logic_vector(2 downto 0);
component sn74ls148
port(i:in std_logic_vector(7 downto 0);
   ys:out std_logic;
   yex:out std_logic;
   q:out std_logic_vector(2 downto 0);
   s:in std_logic);
end component;
begin
process(s16_4,data_in)
begin
b<=i(7) and i(6) and  i(5) and i(4) and i(3) and i(2) and i(1) and i(0) ;
c<=i(15) and i(14) and  i(13) and i(12) and i(11) and i(10) and i(9) and i(8) ;
u1:sn74ls148 port map(i=>b,ys=>ys_temp,yex=>yex_temp,q=>d,s=>ys_temp1);
u2:sn74ls148 port map(i=>c,ys=>ys_temp,yex=>yex_temp1,q=>e,ys_temp1=>s;
data_out(3)<=not yex;
data_out(2)<=not (d(2) and e(2));
data_out(1)<=not (d(1) and e(1));
data_out(0)<=not (d(0) and e(0));
end process;
end rtl;