1 files changed, 59 insertions, 37 deletions
diff --git a/sw/cpld/address_decoder.vhd b/sw/cpld/address_decoder.vhd
index 2c80f86..5f32637 100644..100755
--- a/sw/cpld/address_decoder.vhd
+++ b/sw/cpld/address_decoder.vhd
@@ -1,37 +1,59 @@
-library ieee;
-use ieee.std_logic_1164.all;
-use ieee.std_logic_arith.all;
-use ieee.std_logic_unsigned.all;
-
-entity ADDRESS_DECODER is
-
-port(
-	-- address input
-	PA: in unsigned(15 downto 0);
-
-	-- chip selects output
-	-- memory
-	CSROMH: out std_logic;
-	CSROML: out std_logic;
-	CSRAM : out std_logic;
-	-- io chips
-	CSUART: out std_logic;
-	CSCTC : out std_logic;
-	CSPIO : out std_logic
-);
-
-end;
-
-architecture Behavioral of ADDRESS_DECODER is
-begin
-	-- memory
-	CSROMH <= 0 when ((PA >= x"0000") and (PA < x"2000"));
-	CSROML <= 0 when ((PA >= x"4000") and (PA < x"4000"));
-	CSRAM  <= 0 when (PA >= x"D000");
-	-- io chips
-	CSUART <= 0 when ((PA >= x"4000") and (PA < x"4008"));
-	-- CSCTC
-	-- CSPIO 
-
-end Behavioral;
-
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.std_logic_arith.all;
+use ieee.std_logic_unsigned.all;
+
+entity ADDRESS_DECODER is
+port(
+	-- address input
+	MMU_IN: in std_logic_vector(15 downto 0);
+	-- address output
+	MMU_OUT: out std_logic_vector(15 downto 12);
+
+	-- other signals
+	IORQ: in std_logic;
+	RD:   in std_logic;
+
+	-- chip selects output
+	-- memory
+	CSROML: out std_logic;
+	CSROMH: out std_logic;
+	CSRAM : out std_logic;
+	-- io chips
+	CSUART: out std_logic;
+	CSCTC : out std_logic;
+	CSPIO : out std_logic
+);
+end;
+
+architecture Behavioral of ADDRESS_DECODER is
+	signal ADDR_IN_LOW  : unsigned (7 downto 0);
+	signal ADDR_IN_HIGH : unsigned (7 downto 0);
+	signal ADDR_IN      : unsigned (15 downto 0);
+begin
+	-- PAGE TABLE (disabled)
+	MMU_OUT <= MMU_IN(15 downto 12);	
+	
+	-- ENABLE SIGNALS
+	ADDR_IN_LOW  <= unsigned(MMU_IN(7 downto 0));
+	ADDR_IN_HIGH <= unsigned(MMU_IN(15 downto 8));
+	ADDR_IN      <= unsigned(MMU_IN);
+
+	-- io chips:
+	---- region 0x0000 - 0x00FF ----
+	
+	CSPIO <= '0' when ((ADDR_IN_LOW >= 16#10#) and (ADDR_IN_LOW < 16#14#) and (IORQ = '0')) else '1';
+	-- CSPIO  <= '0' when ((ADDR_IN >= 16#0010#) and (ADDR_IN < 16#0014#)) else '1';
+	-- CSCTC  <= '0' when ((ADDR_IN >= 16#4100#) and (ADDR_IN < 16#4200#)) else '1'; -- test address range
+	--CSUART <= '0' when ((ADDR_IN >= 16#4200#) and (ADDR_IN < 16#4300#)) else '1'; -- test address range
+
+	-- read only memory:
+	---- region 0x0000 - 0x4000 ----
+	CSROML <= '0' when ((ADDR_IN >= 16#0000#) and (ADDR_IN < 16#2000#)) else '1';
+	CSROMH <= '0' when ((ADDR_IN >= 16#2000#) and (ADDR_IN < 16#4000#)) else '1';
+
+	-- random access memory:
+	---- region 0x8000 - 0xFFFF ----
+	CSRAM  <= '0' when (ADDR_IN >= 16#8000#) else '1';
+end Behavioral;
+