Subversion Repositories tinycpu

--RAM module

--4096*8 bit file

--simultaneous write/read support

--16 bit or 8 bit data bus

--16 bit address bus

--On Reset, will load a "default" RAM image

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use ieee.std_logic_arith.all;

use IEEE.NUMERIC_STD.ALL;

use ieee.std_logic_unsigned.all;

entity memory is

  port(

    Address: in std_logic_vector(15 downto 0); --memory address

    Write: in std_logic; --write or read

    UseTopBits: in std_logic;  --if 1, top 8 bits of data is ignored and not written to memory

    Clock: in std_logic;

    DataIn: in std_logic_vector(15 downto 0);

    DataOut: out std_logic_vector(15 downto 0);

    Reset: in std_logic

  );

end memory;

architecture Behavioral of memory is

  constant SIZE : integer := 4096;

  type memorytype is array(0 to (size-1)) of std_logic_vector(7 downto 0);

  signal mem: memorytype;

begin

  writemem: process(Reset,Write, Address, UseTopBits, Clock)

    variable addr: integer;

  begin

    addr := conv_integer(Address);

    if(addr>size-1) then

      addr:=0;

    end if;

    if(rising_edge(Clock)) then

      if(Reset ='1') then

        mem <= (others => "00000000");

      elsif( Write='1') then

        mem(conv_integer(addr)) <= DataIn(7 downto 0);

        if(UseTopBits='1') then

          mem(conv_integer(addr)+1) <= DataIn(15 downto 8);

        end if;

      end if;

    end if;

  end process;

  readmem: process(Reset,Address,Write,Clock)

    variable addr: integer;

  begin

    addr := conv_integer(Address);

    if(addr>size-1) then

      addr:=0;

    end if;

    if(Reset='1') then

      DataOut <= (others => '0');

    elsif(Write='0') then

      DataOut <= mem(conv_integer(addr)+1) & mem(conv_integer(addr));

    else

      DataOut <= (others => '0');

    end if;

  end process;

end Behavioral;