i2c_shift.vhd

这是一个I2C串行数据通信协议以VHDL硬件描述语言实现的IP核

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity i2c_shift is
port(
     fcore,reset:in std_logic;
     shift_en:in std_logic;
     scl,shift_i:out std_logic
    );
end i2c_shift;
architecture behav of i2c_shift is
type t_states is (a,b,c,d);
signal t_state_b: t_states;
signal counta:std_logic_vector(7 downto 0);
begin
process(reset,fcore)
begin
if(reset='1') then
 counta<=(others=>'0');
elsif rising_edge(fcore) then
 if(shift_en='1') then
  t_state_b<=a;
  counta<=counta+1;
  case t_state_b is
  when a=>
   scl<='0';
   shift_i<='0';
   if(counta="00011101") then
    t_state_b<=b;
   else
    t_state_b<=a;
   end if;
  when b=>
   scl<='1';
   if(counta="00110001") then
    t_state_b<=c;
   else
    t_state_b<=b;
   end if;
  when c=>
   scl<='1';
   if(counta="01000101") then
    t_state_b<=d;
       else
    t_state_b<=c;
   end if;
  when d=>
   scl<='0';
   if(counta="01100010") then
    shift_i<='1';
   end if;
   if(counta="01100011") then
    counta<=(others=>'0');
   else
    t_state_b<=d;
   end if;
  end case;
else 
 scl<='0';
 shift_i<='0';
 end if;
 end if;
end process;
end behav;