txd5.vhd

异步发送电路是基于MAXPLUS2软件开发的一种实用电路,已经编译成功,可使用.

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity  txd5 is
  port(indata:in std_logic_vector(7 downto 0);
    cs,wr,clock:in std_logic;
    txd,ti:out std_logic);
end txd5;
architecture behave of txd5 is
  signal sig_count:std_logic_vector(3 downto 0);
  signal sig_ti,sig_txd,sig_buffer,sig_mark:std_logic;
  signal sig_txddata:std_logic_vector(9 downto 0);
begin 
  process (clock)
   begin 
   if(clock'event and clock='1')then
   if(cs='0')then
    if(sig_buffer='0')then
    if(wr='1')then
      for i in 8 downto 1 loop
 sig_txddata(i)<=indata(i-1);
 if(i=8)then
    sig_mark<=sig_txddata(i);
 else
    sig_mark<=sig_mark xor sig_txddata(i);
 end if;
     end loop;
sig_txddata(9)<='0';
if(sig_mark='0')then
    sig_txddata(0)<='0';
else
    sig_txddata(0)<='1';
end if;
sig_buffer<='1';
     end if;
     else
sig_txd<=sig_txddata(9);
for i in 9 downto 1 loop
sig_txddata(i)<=sig_txddata(i-1);
      end loop;
      sig_txddata(0)<='1';
if(sig_count="1011")then
       sig_count<="0000";
       sig_ti<='0';
       elsif(sig_count="0000" and sig_ti='0')then
sig_buffer<='0';
sig_ti<='1';
    else
sig_count<=sig_count+'1';
sig_ti<='1';
end if;
   end if;
end if;
end if;
end process;
process
  begin
if(sig_ti='0')then
     txd<='1';
else txd<=sig_txd;
end if;
end process;
ti<= sig_ti;
end behave;