--===========================================================================----
--
--  S Y N T H E Z I A B L E    spp - Simple Parallel Port
--
--  www.OpenCores.Org - September 2003
--  This core adheres to the GNU public license  
--
-- File name      : spp.vhd
--
-- Purpose        : Simple Parallel Port for System09
--
-- Dependencies   : ieee.Std_Logic_1164
--                  ieee.std_logic_unsigned
--
-- Uses           : None
--
-- Author         : John E. Kent      
--                  dilbert57@opencores.org      
--
--===========================================================================----
--
-- Revision History:
--===========================================================================--
--
-- Version 0.1 - 6th Sep 2008
--  Generated from ioport.vhd
--
--===========================================================================
--
--  Parallel printer port pin assignment
-- 
--  Pin No (DB25) SPP Signal      EPP Signal    Direction Register  Bit Inverted
--  1 	          nStrobe 	     Write_n       Out       Control-0 Yes
--  2 	          Data0           Data0         In/Out    Data-0 	No
--  3 	          Data1           Data1         In/Out    Data-1 	No
--  4 	          Data2           Data2         In/Out    Data-2 	No
--  5 	          Data3           Data3         In/Out    Data-3 	No
--  6 	          Data4           Data4         In/Out    Data-4 	No
--  7 	          Data5           Data5         In/Out    Data-5 	No
--  8 	          Data6           Data6         In/Out    Data-6 	No
--  9 	          Data7           Data7         In/Out    Data-7 	No
--  10 	          nAck            Interrupt     In        Status-6  No
--  11 	          Busy            Wait          In        Status-7  Yes
--  12 	          Paper-Out       Spare         In        Status-5  No
--  13 	          Select          Spare         In        Status-4  No
-- 
--  14 	          Linefeed        Data_Strobe_n Out       Control-1 Yes
--  15 	          nError          Spare         In        Status-3  No
--  16             nInitialize     Reset         Out       Control-2 No
--  17             nSelect-Printer Addr_Strobe_n Out       Control-3 Yes
--  18-25          Ground          Ground        -         -         -
-- 
--  Address                              MSB                         LSB
--                                 Bit:    7   6   5   4   3   2   1   0
-- Base   (SPP Data port)    Write Pin: 	 9   8   7   6   5   4   3   2
-- Base+1 (SPP Status port)  Read  Pin:  ~11  10  12  13  15 				
-- Base+2 (SPP Control port) Write Pin:                  ~17  16 ~14  ~1
-- Base+3 (EPP Address port) R/W
-- Base+4 (EPP Data port)    R/W
-- 
--  ~ indicates a hardware inversion of the bit.
-- 

library ieee;
  use ieee.std_logic_1164.all;
  use ieee.std_logic_unsigned.all;

entity spp is
	port (	
	 clk       : in  std_logic;
    rst       : in  std_logic;
    cs        : in  std_logic;
    rw        : in  std_logic;
    addr      : in  std_logic_vector(2 downto 0);
    data_in   : in  std_logic_vector(7 downto 0);
	 data_out  : out std_logic_vector(7 downto 0);
	 spp_data  : out std_logic_vector(7 downto 0);
	 spp_stat  : in  std_logic_vector(7 downto 3);
	 spp_ctrl  : out std_logic_vector(3 downto 0);
	 hold      : out std_logic;
    irq       : out std_logic
	 );
end;

architecture rtl of spp is

signal spp_data_reg : std_logic_vector(7 downto 0);
signal spp_stat_reg : std_logic_vector(7 downto 3);
signal spp_ctrl_reg : std_logic_vector(3 downto 0);

begin


--------------------------------
--
-- read I/O port
--
--------------------------------

spp_read : process( addr,
                    spp_data_reg, spp_stat_reg, spp_ctrl_reg,
						  spp_stat )
begin
      spp_stat_reg(6 downto 3) <=     spp_stat(6 downto 3);
      spp_stat_reg(7)          <= not spp_stat(7);
      case addr is
	     when "000" =>
          data_out <= spp_data_reg;

		  when "001" =>
          data_out <= spp_stat_reg & "000";

	     when "010" =>
		    data_out <= "0000" & spp_ctrl_reg;

		  when others =>
		    data_out <= (others=> '0');
		end case;
      hold <= '0';
		irq  <= '0';
end process;

---------------------------------
--
-- Write I/O ports
--
---------------------------------

spp_write : process( clk, rst, addr, cs, rw, data_in,
                     spp_data_reg, spp_ctrl_reg )
begin
  if clk'event and clk = '0' then
    if rst = '1' then
      spp_data_reg <= "00000000";
      spp_ctrl_reg <= "0000";
    elsif cs = '1' and rw = '0' then
      case addr is
	     when "000" =>
		    spp_data_reg <= data_in;
		  when "010" =>
		    spp_ctrl_reg <= data_in(3 downto 0);
		  when others =>
		    null;
		end case;
	 end if;
  end if;
  spp_data    <=     spp_data_reg;
  spp_ctrl(0) <= not spp_ctrl_reg(0);
  spp_ctrl(1) <= not spp_ctrl_reg(1);
  spp_ctrl(2) <=     spp_ctrl_reg(2);
  spp_ctrl(3) <= not spp_ctrl_reg(3);
end process;

end rtl;
	
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