Adress Decoder

LIBRARY ieee;
USE ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity AddressDecoder is
	Port (
		Address 						: in Std_logic_vector(31 downto 0) ;		-- address directly from 68k

		-- outputs to activate rom,ram, sram, dram etc as per labs

		OnChipRomSelect_H 		: out Std_Logic ;
		OnChipRamSelect_H 		: out Std_Logic ;
		DramSelect_H 				: out Std_logic ;
		DE2_512KSRamSelect_H 	: out Std_logic;
		IOSelect_H 					: out Std_logic;
		FlashSelect_H 				: out Std_logic;
		DMASelect_L 				: out Std_logic;
		GraphicsCS_L 				: out Std_logic
	);
end ;


architecture bhvr of AddressDecoder is
Begin
	process(Address)
	begin

		-- default values for all memory and IO Select Signals (default is NOT activated)
		-- override as required using if-endif statements based on range of addresses issued by 68k

		OnChipRomSelect_H <= '0' ;
		OnChipRamSelect_H <= '0' ;
		DramSelect_H <= '0' ;
		DE2_512KSRamSelect_H <= '0';
		IOSelect_H <= '0' ;
		FlashSelect_H <= '0' ;
		DMASelect_L <= '1' ;
		GraphicsCS_L <= '1' ;

		if(Address( 31 downto 15) = B"0000_0000_0000_0000_0") then 	-- ON CHIP ROM address hex 0000 0000 - 0000 7FFF 32k full decoding
			OnChipRomSelect_H <= '1' ;											-- DO NOT CHANGE - debugger expects rom at this address
		end if ;

		if(Address( 31 downto 14) = B"0000_0000_0000_0001_00") then -- address hex 0001 0000 - 0001 3FFF 16k full decoding
			OnChipRamSelect_H <= '1' ;											-- DO NOT CHANGE - debugger expects Ram at this address
		end if ;

		if(Address(31 downto 16) = B"0000_0000_0100_0000") then 		-- address hex 0040 0000 - 0040 FFFF Partial decoding
			IOSelect_H <= '1' ;													-- DO NOT CHANGE - debugger expects IO at this address
		end if ;

		if(Address(31 downto 19) = B"0000_0000_1000_0") then		   -- Addross hex 0080 000 - 0087 FFFF Partial Decoding
		DE2_512KSRamSelect_H <= '1';
		end if;

		if(Address(31 downto 8) = B"0000_0000_0001_0") then
			if(Address(8) = '0') then
		FlashSelect_H <= '1';
		end if;
		end if;

		-- add other decoder signals here for Sram, Dram, Flash, Graphics etc to fix their range of addresses (see relavent Lab/Assignment)
		-- SRam (i.e. DE2_512KSramSelect_H) should be active high when 68k accesses address in range 00800000 - 0087FFFF

	end process ;
END ;