AppleIISd/VHDL/AddressDecoder.vhd

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2017-10-10 20:32:24 +00:00
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-- Company:
-- Engineer:
--
-- Create Date: 22:03:22 10/10/2017
-- Design Name:
-- Module Name: AddressDecoder - Behavioral
-- Project Name:
-- Target Devices:
-- Tool versions:
-- Description:
--
-- Dependencies:
--
-- Revision:
-- Revision 0.01 - File Created
-- Additional Comments:
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;
-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;
entity AddressDecoder is
Port ( A : in std_logic_vector (10 downto 8);
B : out std_logic_vector (10 downto 8);
RNW : in std_logic;
NDEV_SEL : in std_logic;
NIO_SEL : in std_logic;
NIO_STB : in std_logic;
NRESET : in std_logic;
DATA_EN : out std_logic;
NG : out std_logic;
NOE : out std_logic);
end AddressDecoder;
architecture Behavioral of AddressDecoder is
signal cfxx : std_logic;
signal noe_int : std_logic;
signal ncs : std_logic;
begin
B <= A when (NIO_STB = '0') else (others => '0');
DATA_EN <= RNW and not NDEV_SEL;
NG <= NDEV_SEL and noe_int;
NOE <= noe_int;
noe_int <= not RNW or not NDEV_SEL or NIO_STB or ncs;
cfxx <= A(8) and A(9) and A(10) and not NIO_STB;
process(NRESET, NIO_SEL, cfxx)
begin
if (NRESET = '0' or cfxx = '1') then
ncs <= '1';
elsif falling_edge(NIO_SEL) then
ncs <= '0';
end if;
end process;
end Behavioral;