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--===========================================================================--
--
--  S Y N T H E Z I A B L E    ioport - Dual 8 Bit parallel i/o port
--
--  www.OpenCores.Org - September 2003
--  This core adheres to the GNU public license  
--
-- File name      : ioport.vhd
--
-- Entity name    : ioport
--
-- Purpose        : Dual 8 bit parallel I/O port with
--                  Data Direction Registers
--                  cs + 0 - porta data
--                  cs + 1 - portb data
--                  cs + 3 - porta direction
--                  cs + 4 - portb direction
--
-- Dependencies   : ieee.std_logic_1164
--                  ieee.std_logic_unsigned
--
-- Uses           : Nothing
--
-- Author         : John Kent - dilbert57@opencores.org
--
-------------------------------------------------------------------------------
-- Revision list
--
-- Revision 0.1 - 11 Oct 2002 - John Kent
-- used a loop counter for data direction & read port signals
--
-- Revision 0.2 - 5 Sept 2003 - John Kent
-- Reduced to 2 x 8 bit ports
--
-- Revision 1.0 - 7 September - John Kent
-- Initial release to open cores
--
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
 
entity ioport is
	port (	
	 clk       : in  std_logic;
    rst       : in  std_logic;
    cs        : in  std_logic;
    rw        : in  std_logic;
    addr      : in  std_logic_vector(1 downto 0);
    data_in   : in  std_logic_vector(7 downto 0);
	 data_out  : out std_logic_vector(7 downto 0);
	 porta_io  : inout std_logic_vector(7 downto 0);
	 portb_io  : inout std_logic_vector(7 downto 0)
	 );
end;
 
architecture ioport_arch of ioport is
signal porta_ddr : std_logic_vector(7 downto 0);
signal portb_ddr : std_logic_vector(7 downto 0);
signal porta_data : std_logic_vector(7 downto 0);
signal portb_data : std_logic_vector(7 downto 0);
 
begin
 
 
--------------------------------
--
-- read I/O port
--
--------------------------------
 
ioport_read : process( addr,
                     porta_ddr, portb_ddr,
							porta_data, portb_data,
						   porta_io, portb_io )
variable count : integer;
begin
      case addr is
	     when "00" =>
		    for count in 0 to 7 loop
            if porta_ddr(count) = '1' then
              data_out(count) <= porta_data(count);
            else
              data_out(count) <= porta_io(count);
            end if;
			 end loop;
 
		  when "01" =>
		    for count in 0 to 7 loop
            if portb_ddr(count) = '1' then
              data_out(count) <= portb_data(count);
            else
              data_out(count) <= portb_io(count);
            end if;
			 end loop;
 
	     when "10" =>
		    data_out <= porta_ddr;
		  when "11" =>
		    data_out <= portb_ddr;
		  when others =>
		    data_out <= "00000000";
		end case;
end process;
 
---------------------------------
--
-- Write I/O ports
--
---------------------------------
 
ioport_write : process( clk, rst, addr, cs, rw, data_in,
                        porta_data, portb_data,
								porta_ddr, portb_ddr )
begin
  if clk'event and clk = '0' then
    if rst = '1' then
      porta_data <= "00000000";
      portb_data <= "00000000";
      porta_ddr <= "00000000";
      portb_ddr <= "00000000";
    elsif cs = '1' and rw = '0' then
      case addr is
	     when "00" =>
		    porta_data <= data_in;
		    portb_data <= portb_data;
		    porta_ddr  <= porta_ddr;
		    portb_ddr  <= portb_ddr;
		  when "01" =>
		    porta_data <= porta_data;
		    portb_data <= data_in;
		    porta_ddr  <= porta_ddr;
		    portb_ddr  <= portb_ddr;
		  when "10" =>
		    porta_data <= porta_data;
		    portb_data <= portb_data;
		    porta_ddr  <= data_in;
		    portb_ddr  <= portb_ddr;
		  when "11" =>
		    porta_data <= porta_data;
		    portb_data <= portb_data;
		    porta_ddr  <= porta_ddr;
		    portb_ddr  <= data_in;
		  when others =>
		    porta_data <= porta_data;
		    portb_data <= portb_data;
		    porta_ddr  <= porta_ddr;
		    portb_ddr  <= portb_ddr;
		end case;
	 else
		    porta_data <= porta_data;
		    portb_data <= portb_data;
		    porta_ddr  <= porta_ddr;
		    portb_ddr  <= portb_ddr;
	 end if;
  end if;
end process;
 
---------------------------------
--
-- direction control port a
--
---------------------------------
porta_direction : process ( porta_data, porta_ddr )
variable count : integer;
begin
  for count in 0 to 7 loop
    if porta_ddr(count) = '1' then
      porta_io(count) <= porta_data(count);
    else
      porta_io(count) <= 'Z';
    end if;
  end loop;
end process;
---------------------------------
--
-- direction control port b
--
---------------------------------
portb_direction : process ( portb_data, portb_ddr )
variable count : integer;
begin
  for count in 0 to 7 loop
    if portb_ddr(count) = '1' then
      portb_io(count) <= portb_data(count);
    else
      portb_io(count) <= 'Z';
    end if;
  end loop;
end process;
---------------------------------
 
end ioport_arch;