Subversion Repositories z80soc

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-- Z80SoC (Z80 System on Chip)

-- Ronivon Candido Costa

-- ronivon.costa@gmail.com

--

-- Version history:

-------------------

-- version 0.7.1

-- 2010 / 11 / 22

-- Change memory layout and increased Rom, using Megawizard plug in manager

-- Memory cores redefined

-- Fixed bug in the video.vhd

-- New rom demo in C (SDCC)

--

-- version 0.7

-- Release Date: 2010 / 02 / 17

-- version 0.6 for for Altera DE1

-- Release Date: 2008 / 05 / 21

--

-- Version 0.5 Beta for Altera DE1

-- Developer: Ronivon Candido Costa

-- Release Date: 2008 / 04 / 16

--

-- Based on the T80 core: http://www.opencores.org/projects.cgi/web/t80

-- This version developed and tested on: Altera DE1 Development Board

--

-- Peripherals configured (Using Ports):

--

--      16 KB Internal ROM      Read            (0x0000h - 0x3FFFh)

--      08 KB INTERNAL VRAM     Write           (0x4000h - 0x5FFFh)

--      32 KB External SRAM     Read/Write      (0x8000h - 0xFFFFh)

--      08 Green Leds           Out             (Port 0x01h)

--      08 Red Leds                     Out             (Port 0x02h)

--      04 Seven Seg displays   Out             (Ports 0x11h and 0x10h)

--      36 Pins GPIO0           In/Out  (Ports 0xA0h, 0xA1h, 0xA2h, 0xA3h, 0xA4h, 0xC0h)

--      36 Pins GPIO1           In/Out  (Ports 0xB0h, 0xB1h, 0xB2h, 0xB3h, 0xB4h, 0xC1h)

--      08 Switches                     In              (Port 0x20h)

--      04 Push buttons         In              (Port 0x30h)

--      01 PS/2 keyboard                In              (Port 0x80h)

--      01 Video write port     In              (Port 0x90h)

--

--  Revision history:

--

-- 2008/05/23 - Modified RAM layout to support new and future improvements

--            - Added port 0x90 to write a character to video.

--            - Cursor x,y automatically updated after writing to port 0x90

--            - Added port 0x91 for video cursor X

--            - Added port 0x92 for video cursor Y

--                - Updated ROM to demonstrate how to use these new resources

--            - Changed ROM to support 14 bit addresses (16 Kb)

--

-- 2008/05/12 - Added support for the Rotary Knob

--            - ROT_CENTER push button (Knob) reserved for RESET

--            - The four push buttons are now available for the user (Port 0x30)

--

-- 2008/05/11 - Fixed access to RAM and VRAM,

--              Released same ROM version for DE1 and S3E

--

-- 2008/05/01 - Added LCD support for Spartan 3E

--

-- 2008/04(21 - Release of Version 0.5-S3E-Beta for Diligent Spartan 3E

--

--      2008/04/17 - Added Video support for 40x30 mode

--

-- 2008/04/16 - Release of Version 0.5-DE1-Beta for Altera DE1

--

-- TO-DO:

-- - Implement hardware control for the A/D and IO pins

-- - Monitor program to introduce Z80 Assmebly codes and run

-- - Serial communication, to download assembly code from PC

-- - Add hardware support for 80x40 Video out

-- - SD/MMC card interface to read/store data and programs

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library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.std_logic_arith.all;

use IEEE.std_logic_unsigned.all;

use work.z80soc_pack.all;

entity  Z80SOC is

        port(

    -- Clocks

    CLOCK_50 : in std_logic;              -- 50 MHz

    -- Buttons and switches

    KEY : in std_logic_vector(3 downto 0);         -- Push buttons

    SW : in std_logic_vector(17 downto 0);          -- Switches

    -- LED displays

    HEX0, HEX1, HEX2, HEX3, HEX4, HEX5, HEX6, HEX7  -- 7-segment displays

                        : out std_logic_vector(6 downto 0);

    LEDG : out std_logic_vector(8 downto 0);       -- Green LEDs

    LEDR : out std_logic_vector(17 downto 0);       -- Red LEDs

    -- RS-232 interface

    UART_TXD : out std_logic;                      -- UART transmitter   

    UART_RXD : in std_logic;                       -- UART receiver

    UART_RTS : in std_logic;                       -- UART RTS

         UART_CTS : in std_logic;                       -- UART CTS

    -- IRDA interface

    -- IRDA_TXD : out std_logic;                      -- IRDA Transmitter

    IRDA_RXD : in std_logic;                       -- IRDA Receiver

    -- SDRAM

    DRAM_BA_0,                                     -- Bank Address 0

    DRAM_BA_1,                                     -- Bank Address 0   

    DRAM_DQM_0,                                     -- Byte Data Mask 0

    DRAM_DQM_1,                                     -- Byte Data Mask 1

    DRAM_DQM_2,                                     -- Byte Data Mask 2

    DRAM_DQM_3,                                     -- Byte Data Mask 3

    DRAM_WE_N,                                     -- Write Enable

    DRAM_CAS_N,                                    -- Column Address Strobe

    DRAM_RAS_N,                                    -- Row Address Strobe

    DRAM_CS_N :   out std_logic;                   -- Chip Select

    DRAM_DQ : inout std_logic_vector(31 downto 0); -- Data Bus

    DRAM_ADDR : out std_logic_vector(12 downto 0); -- Address Bus 

    DRAM_CLK,                                      -- Clock

    DRAM_CKE : out std_logic;                      -- Clock Enable

    -- FLASH

    FL_DQ : inout std_logic_vector(7 downto 0);      -- Data bus

    FL_ADDR : out std_logic_vector(22 downto 0);     -- Address bus

         FL_RY : in std_logic;

         FL_WP_N,

    FL_WE_N,                                         -- Write Enable

    FL_RST_N,                                        -- Reset

    FL_OE_N,                                         -- Output Enable

    FL_CE_N : out std_logic;                         -- Chip Enable

    -- SRAM

    SRAM_DQ : inout std_logic_vector(15 downto 0); -- Data bus 16 Bits

    SRAM_ADDR : out std_logic_vector(SRAM_width - 1 downto 0); -- Address bus 18 Bits

    SRAM_UB_N,                                     -- High-byte Data Mask 

    SRAM_LB_N,                                     -- Low-byte Data Mask 

    SRAM_WE_N,                                     -- Write Enable

    SRAM_CE_N,                                     -- Chip Enable

    SRAM_OE_N : out std_logic;                     -- Output Enable

    -- SD card interface

    SD_DAT0 : in std_logic;      -- SD Card Data      SD "DAT 0/DataOut"

    SD_DAT1 : inout std_logic;      -- SD Card Data   SD "DAT 1"

    SD_DAT2 : inout std_logic;    -- SD Card Data 3   SD "DAT 2"

    SD_DAT3 : out std_logic;    -- SD Card Data 3    SD "DAT 3/nCS"    

         SD_CMD : out std_logic;     -- SD Card Command   SD "CMD/DataIn"

    SD_CLK : out std_logic;     -- SD Card Clock     SD "CLK"

    -- PS/2 port

    PS2_DAT,                    -- Data

    PS2_CLK : inout std_logic;     -- Clock

         PS2_DAT2,                    -- Data

    PS2_CLK2 : inout std_logic;     -- Clock

    -- VGA output

         VGA_SYNC_N,

         VGA_CLK,

         VGA_BLANK_N,

    VGA_HS,                                             -- H_SYNC

    VGA_VS : out std_logic;                             -- SYNC

    VGA_R,                                              -- Red[7:0]

    VGA_G,                                              -- Green[7:0]

    VGA_B : out std_logic_vector(7 downto 0);           -- Blue[7:0]

    -- Audio CODEC

    AUD_ADCLRCK : inout std_logic;                      -- ADC LR Clock

    AUD_ADCDAT : in std_logic;                          -- ADC Data

    AUD_DACLRCK : inout std_logic;                      -- DAC LR Clock

    AUD_DACDAT : out std_logic;                         -- DAC Data

    AUD_BCLK : inout std_logic;                         -- Bit-Stream Clock

    AUD_XCK : out std_logic;                                                                      -- Chip Clock

    LCD_RS             : OUT    std_logic;

    LCD_EN             : OUT    std_logic;

    LCD_RW             : OUT    std_logic;

         LCD_ON             : OUT    std_logic;

    LCD_BLON           : OUT    std_logic; -- lcd on DE2 do not support this signal

    LCD_DATA           : INOUT  STD_LOGIC_VECTOR(7 DOWNTO 0));

end Z80SOC;

architecture rtl of Z80SOC is

        component T80se

        generic(

                Mode : integer := 0;     -- 0 => Z80, 1 => Fast Z80, 2 => 8080, 3 => GB

                T2Write : integer := 1; -- 0 => WR_n active in T3, /=0 => WR_n active in T2

                IOWait : integer := 1   -- 0 => Siomngle cycle I/O, 1 => Std I/O cycle

        );

        port(

                RESET_n : in std_logic;

                CLK_n           : in std_logic;

                CLKEN           : in std_logic;

                WAIT_n  : in std_logic;

                INT_n           : in std_logic;

                NMI_n           : in std_logic;

                BUSRQ_n : in std_logic;

                M1_n            : out std_logic;

                MREQ_n  : out std_logic;

                IORQ_n  : out std_logic;

                RD_n            : out std_logic;

                WR_n            : out std_logic;

                RFSH_n  : out std_logic;

                HALT_n  : out std_logic;

                BUSAK_n : out std_logic;

                A                       : out std_logic_vector(15 downto 0);

                DI                      : in std_logic_vector(7 downto 0);

                DO                      : out std_logic_vector(7 downto 0)

        );

        end component;

        component rom

        port (

                clock   : in std_logic;

                address : in std_logic_vector(13 downto 0);

                q       : out std_logic_vector(7 downto 0));

        end component;

    component clk_div

    PORT

    (

        clock_in_50Mhz          : IN    STD_LOGIC;

        clock_25MHz             : OUT   STD_LOGIC;

                clock_10MHz             : OUT   STD_LOGIC;

                clock_357MHz            : OUT   STD_LOGIC;

        clock_1MHz              : OUT   STD_LOGIC;

        clock_100KHz            : OUT   STD_LOGIC;

        clock_10KHz             : OUT   STD_LOGIC;

        clock_1KHz              : OUT   STD_LOGIC;

        clock_100Hz             : OUT   STD_LOGIC;

        clock_10Hz              : OUT   STD_LOGIC;

        clock_1Hz               : OUT   STD_LOGIC);

    end component;

        component decoder_7seg

        port (

                NUMBER          : in   std_logic_vector(3 downto 0);

                HEX_DISP                : out  std_logic_vector(6 downto 0));

        end component;

        component ps2kbd

        port (

                        keyboard_clk    : inout std_logic;

                        keyboard_data   : inout std_logic;

                        clock                           : in std_logic;

                        clkdelay                        : in std_logic;

                        reset                           : in std_logic;

                        read                            : in std_logic;

                        scan_ready              : out std_logic;

                        ps2_ascii_code  : out std_logic_vector(7 downto 0));

        end component;

        component vram

        port

        (

                rdaddress               : IN STD_LOGIC_VECTOR (12 DOWNTO 0);

                wraddress               : IN STD_LOGIC_VECTOR (12 DOWNTO 0);

                rdclock                 : IN STD_LOGIC;

                wrclock                 : IN STD_LOGIC;

                data                    : IN STD_LOGIC_VECTOR (7 DOWNTO 0);

                wren                    : IN STD_LOGIC;

                q                               : OUT STD_LOGIC_VECTOR (7 DOWNTO 0)

        );

        end component;

        component charram

        port (

                data                    : IN STD_LOGIC_VECTOR (7 DOWNTO 0);

                rdaddress               : IN STD_LOGIC_VECTOR (10 DOWNTO 0);

                rdclock                 : IN STD_LOGIC ;

                wraddress               : IN STD_LOGIC_VECTOR (10 DOWNTO 0);

                wrclock                 : IN STD_LOGIC;

                wren                    : IN STD_LOGIC;

                q                               : OUT STD_LOGIC_VECTOR (7 DOWNTO 0));

        end component;

        COMPONENT video

        PORT (

                CLOCK_25                : IN STD_LOGIC;

                VRAM_DATA               : IN STD_LOGIC_VECTOR(7 DOWNTO 0);

                VRAM_ADDR               : OUT STD_LOGIC_VECTOR(13 DOWNTO 0);

                VRAM_CLOCK              : OUT STD_LOGIC;

                VRAM_WREN               : OUT STD_LOGIC;

                CRAM_DATA               : IN STD_LOGIC_VECTOR(7 DOWNTO 0);

                CRAM_ADDR               : OUT STD_LOGIC_VECTOR(10 DOWNTO 0);

                CRAM_WEB                : OUT STD_LOGIC;

                VGA_R,

                VGA_G,

                VGA_B                   : OUT STD_LOGIC_VECTOR(3 DOWNTO 0);

                VGA_HS,

                VGA_VS                  : OUT STD_LOGIC);

        END COMPONENT;

        COMPONENT PLL_Clocks

        PORT

        (

                inclk0          : IN STD_LOGIC  := '0';

                c0                      : OUT STD_LOGIC;

                c1                      : OUT STD_LOGIC;

                c2                      : OUT STD_LOGIC

        );

        END COMPONENT;

        COMPONENT LCD

   PORT(

      reset             : IN     std_logic;  -- Map this Port to a Switch within your [Port Declarations / Pin Planer]  

      CLOCK_50          : IN     std_logic;  -- Using the DE2 50Mhz Clk, in order to Genreate the 400Hz signal... clk_count_400hz reset count value must be set to:  <= x"0F424"

      LCD_RS            : OUT    std_logic;

      LCD_EN            : OUT    std_logic;

      LCD_RW            : OUT    std_logic;

      LCD_ON            : OUT    std_logic;

      LCD_BLON          : OUT    std_logic;

      LCD_DATA          : INOUT         STD_LOGIC_VECTOR(7 DOWNTO 0);

                lcd_on_sig                      : IN            STD_LOGIC;

           next_char                    : IN            STD_LOGIC_VECTOR(7 DOWNTO 0);

                char_count                      : OUT           STD_LOGIC_VECTOR(4 downto 0);

                clk400hz                                : OUT           STD_LOGIC);

        END COMPONENT;

        signal MREQ_n   : std_logic;

        signal IORQ_n   : std_logic;

        signal RD_n             : std_logic;

        signal WR_n             : std_logic;

        signal MWr_n    : std_logic;

        signal Rst_n_s  : std_logic;

        signal Clk_Z80  : std_logic;

        signal DI_CPU   : std_logic_vector(7 downto 0);

        signal DO_CPU   : std_logic_vector(7 downto 0);

        signal A                : std_logic_vector(15 downto 0);

        signal One              : std_logic;

        signal D_ROM    : std_logic_vector(7 downto 0);

        signal rom_data : std_logic_vector(7 downto 0);

        signal rom_wren : std_logic;

        signal clk_count_400hz: std_logic_vector(19 downto 0);

        signal clk100mhz        : std_logic;

        signal clk25mhz : std_logic;

        signal clk1mhz          : std_logic;

        signal clk10mhz : std_logic;

        signal clk100hz : std_logic;

        signal clk10hz          : std_logic;

        signal clk1hz           : std_logic;

        signal clk357mhz   : std_logic;

        signal HEX_DISP0        : std_logic_vector(6 downto 0);

        signal HEX_DISP1        : std_logic_vector(6 downto 0);

        signal HEX_DISP2        : std_logic_vector(6 downto 0);

        signal HEX_DISP3        : std_logic_vector(6 downto 0);

        signal HEX_DISP4        : std_logic_vector(6 downto 0);

        signal HEX_DISP5        : std_logic_vector(6 downto 0);

        signal HEX_DISP6        : std_logic_vector(6 downto 0);

        signal HEX_DISP7        : std_logic_vector(6 downto 0);

        signal NUMBER0          : std_logic_vector(3 downto 0);

        signal NUMBER1          : std_logic_vector(3 downto 0);

        signal NUMBER2          : std_logic_vector(3 downto 0);

        signal NUMBER3          : std_logic_vector(3 downto 0);

        signal NUMBER4          : std_logic_vector(3 downto 0);

        signal NUMBER5          : std_logic_vector(3 downto 0);

        signal NUMBER6          : std_logic_vector(3 downto 0);

        signal NUMBER7          : std_logic_vector(3 downto 0);

        --signal GPIO_0_buf_in  : std_logic_vector(35 downto 0);

        --signal GPIO_1_buf_in  : std_logic_vector(35 downto 0);

        signal  vram_addra              : std_logic_vector(15 downto 0);

        signal  vram_addrb              : std_logic_vector(13 downto 0);

        signal  vram_dina               : std_logic_vector(7 downto 0);

        signal  vram_dinb               : std_logic_vector(7 downto 0);

        signal  vram_douta              : std_logic_vector(7 downto 0);

        signal  vram_doutb              : std_logic_vector(7 downto 0);

        signal  vram_wea                : std_logic;

        signal  vram_web                : std_logic;

        signal  vram_clka               : std_logic;

        signal  vram_clkb               : std_logic;

--      signal vram_douta_reg   : std_logic_vector(7 downto 0); 

        signal cram_addra               : std_logic_vector(15 downto 0);

        signal cram_addrb               : std_logic_vector(15 downto 0);

        signal cram_dina                : std_logic_vector(7 downto 0);

        signal cram_dinb                : std_logic_vector(7 downto 0);

        signal cram_douta               : std_logic_vector(7 downto 0);

        signal cram_doutb               : std_logic_vector(7 downto 0);

        signal cram_wea                 : std_logic;

        signal cram_web                 : std_logic;

        signal cram_clka                : std_logic;

        signal cram_clkb                : std_logic;

        -- PS/2 Keyboard

        signal ps2_read                         : std_logic;

        signal ps2_scan_ready           : std_logic;

        signal ps2_ascii_sig            : std_logic_vector(7 downto 0);

        signal ps2_ascii_reg1           : std_logic_vector(7 downto 0);

        signal ps2_ascii_reg            : std_logic_vector(7 downto 0);

        -- LCD signals

        type character_string is array ( 0 to 31 ) of STD_LOGIC_VECTOR( 7 downto 0 );

        signal lcdvram                          : character_string;

        signal lcdaddr_w_sig            : std_logic_vector(15 downto 0);

        signal lcdaddr_sig                              : std_logic_vector(15 downto 0) := LCD_value;

        signal clk400hz                                 : std_logic;

        signal char_count_sig                   : std_logic_vector(4 downto 0);

        signal next_char_sig                            : std_logic_vector(7 downto 0);

        signal temp                                                     : std_logic;

        signal Z80SOC_Arch_reg                  : std_logic_vector(2 downto 0)  := Z80SOC_Arch_value;   -- "000" = DE1, "001" = S3E, "010" = DE2115

        signal RAMTOP_reg                                       : std_logic_vector(15 downto 0) := RAMTOP_value;

        signal RAMBOTT_reg                              : std_logic_vector(15 downto 0) := RAMBOTT_value;

        signal LCD_reg                                          : std_logic_vector(15 downto 0) := LCD_value;

        signal VRAM_reg                                 : std_logic_vector(15 downto 0) := VRAM_value;

        signal STACK_reg                                        : std_logic_vector(15 downto 0) := STACK_value;

        signal CHARRAM_reg                              : std_logic_vector(15 downto 0) := CHARRAM_value;

        signal VRAMNXTCHAR_reg                  : std_logic_vector(15 downto 0);

        signal CURX_reg                                 : std_logic_vector(7 downto 0);

        signal CURY_reg                                 : std_logic_vector(7 downto 0);

        signal STDOUT_reg                                       : std_logic_vector(7 downto 0);

        signal LCDON_reg                                        : std_logic;

begin

        -- required signals for DE2-115

        VGA_BLANK_N <= '1';

        VGA_CLK <= clk25mhz;

        -- 

        STDOUT_reg <= DO_CPU when (A = x"57CD" and Wr_n = '0' and MReq_n = '0');

        CURX_reg   <= DO_CPU when (A = x"57CF" and Wr_n = '0' and MReq_n = '0');

        CURY_reg   <= DO_CPU when (A = x"57CE" and Wr_n = '0' and MReq_n = '0');

        VRAMNXTCHAR_reg(7 DOWNTO 0)  <= DO_CPU when (A = x"57D0" and Wr_n = '0' and MReq_n = '0');

        VRAMNXTCHAR_reg(15 DOWNTO 8) <= DO_CPU when (A = x"57D1" and Wr_n = '0' and MReq_n = '0');

        -- Modo Turbo 10Mhz

        Clk_Z80 <= clk357mhz when SW(16) = '0' else clk10mhz;

        LEDR(17) <= SW(17);

        LEDR(16) <= SW(16);

        --Z80SOC_Arch_reg <= Z80SOC_Arch_addr;  -- "000" = DE1, "001" = S3E, "010" = DE2115

        Rst_n_s <= not SW(17);

        HEX0 <= HEX_DISP0;

        HEX1 <= HEX_DISP1;

        HEX2 <= HEX_DISP2;

        HEX3 <= HEX_DISP3;

        HEX4 <= HEX_DISP4;

        HEX5 <= HEX_DISP5;

        HEX6 <= HEX_DISP6;

        HEX7 <= HEX_DISP7;

--      Write into VRAM and System Variables

        vram_addra <= A - VRAM_value;

        vram_dina  <= DO_CPU;

        vram_wea   <= '0' when (A >= VRAM_value and A < LCD_value and Wr_n = '0' and MReq_n = '0') else

                  '1';

-- Write into char ram

        cram_addra      <= A - CHARRAM_value;

        cram_dina       <= DO_CPU;

        cram_wea        <= '0' when (A >= CHARRAM_value and A < RAMBOTT_value and Wr_n = '0' and MReq_n = '0') else '1';

-- Write into LCD video ram

        --LCD_ON <= KEY(3);

        lcdvram(CONV_INTEGER(A - LCD_value)) <= DO_CPU when A >= LCD_value and (A < LCD_value + 32) and Wr_n = '0' and MReq_n = '0';

        -- SRAM control signals

        -- SRAM will store data for video, characters patterns and RAM (only on DE1 version)

        -- Due to limitation in dual-port block rams on this platform

        SRAM_ADDR(15 downto 0) <= A - RAMBOTT_value;

        SRAM_DQ(7 downto 0) <= DO_CPU when (Wr_n = '0' and MREQ_n = '0' and A >= RAMBOTT_value) else (others => 'Z');

        SRAM_WE_N <= '0' when (Wr_n = '0' and MREQ_n = '0' and A >= RAMBOTT_value) else '1';

        SRAM_OE_N <= '0' when (Rd_n = '0' and MREQ_n = '0' and A >= RAMBOTT_value) else '1';

        SRAM_DQ(15 downto 8) <= (others => 'Z');

        SRAM_ADDR(19 downto 16) <= "0000";

        SRAM_UB_N <= '1';

        SRAM_LB_N <= '0';

        SRAM_CE_N <= '0';

        -- Input to Z80

        DI_CPU <= ("00000" & Z80SOC_Arch_reg) when (Rd_n = '0' and MREQ_n = '0' and A = Z80SOC_Arch_addr) else

                        ps2_ascii_reg when (Rd_n = '0' and MREQ_n = '0' and A = KEYPRESS_addr) else

                        RAMTOP_reg(7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = RAMTOP_addr) else

                        RAMTOP_reg(15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = RAMTOP_addr + 1)) else

                        RAMBOTT_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = RAMBOTT_addr) else

                        RAMBOTT_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = RAMBOTT_addr + 1)) else

                        LCD_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = LCD_addr) else

                        LCD_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = LCD_addr + 1)) else

                        VRAM_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = VRAM_addr) else

                        VRAM_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = VRAM_addr + 1)) else

                        CHARRAM_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = CHARRAM_addr) else

                        CHARRAM_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = CHARRAM_addr + 1)) else

                        STACK_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = STACK_addr) else

                        STACK_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and (A = STACK_addr + 1)) else

                        VRAMNXTCHAR_reg (7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and A = x"57D0") else

                        VRAMNXTCHAR_reg (15 downto 8) when (Rd_n = '0' and MREQ_n = '0' and A = x"57D1") else

                        CURX_reg when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A = x"57CF") else

                        CURY_reg when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A = x"57CE") else

                        STDOUT_reg when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A = x"57CD") else

                        D_ROM when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A < VRAM_value) else

                        --vram_doutb when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and (A >= VRAM_value + 4800) and A < LCD_value) else

                        SRAM_DQ(7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A >= RAMBOTT_value) else

                        SW(7 downto 0) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"20") else

                        SW(15 downto 8) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"21") else

                        ("0000" & not KEY) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"30") else

                        --ps2_ascii_reg when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"80") else

                        "ZZZZZZZZ";

        -- Process to latch leds and hex displays

        pinout_process: process(Clk_Z80)

        variable NUMBER0_sig    : std_logic_vector(3 downto 0);

        variable NUMBER1_sig    : std_logic_vector(3 downto 0);

        variable NUMBER2_sig    : std_logic_vector(3 downto 0);

        variable NUMBER3_sig    : std_logic_vector(3 downto 0);

        variable NUMBER4_sig    : std_logic_vector(3 downto 0);

        variable NUMBER5_sig    : std_logic_vector(3 downto 0);

        variable NUMBER6_sig    : std_logic_vector(3 downto 0);

        variable NUMBER7_sig    : std_logic_vector(3 downto 0);

        variable LEDG_sig               : std_logic_vector(7 downto 0);

        variable LEDR_sig               : std_logic_vector(15 downto 0);

        --variable GPIO_0_buf_out: std_logic_vector(35 downto 0);

        --variable GPIO_1_buf_out: std_logic_vector(35 downto 0);

        begin

                if Clk_Z80'event and Clk_Z80 = '1' then

                  if IORQ_n = '0' and MREQ_n = '1' and Wr_n = '0' then

                        -- LEDG

                        if A(7 downto 0) = x"01" then

                                LEDG_sig := DO_CPU;

                        -- LEDR

                        elsif A(7 downto 0) = x"02" then

                                LEDR_sig(7 downto 0) := DO_CPU;

                        elsif A(7 downto 0) = x"03" then

                                LEDR_sig(15 downto 8) := DO_CPU;

                        -- HEX1 and HEX0

                        elsif A(7 downto 0) = x"10" then

                                NUMBER0_sig := DO_CPU(3 downto 0);

                                NUMBER1_sig := DO_CPU(7 downto 4);

                        -- HEX3 and HEX2

                        elsif A(7 downto 0) = x"11" then

                                NUMBER2_sig := DO_CPU(3 downto 0);

                                NUMBER3_sig := DO_CPU(7 downto 4);

                        -- HEX5 and HEX4

                        elsif A(7 downto 0) = x"12" then

                                NUMBER4_sig := DO_CPU(3 downto 0);

                                NUMBER5_sig := DO_CPU(7 downto 4);

                        -- HEX7 and HEX6

                        elsif A(7 downto 0) = x"13" then

                                NUMBER6_sig := DO_CPU(3 downto 0);

                                NUMBER7_sig := DO_CPU(7 downto 4);

                        elsif A(7 downto 0) = x"15" then

                                LCDON_reg <= DO_CPU(0);

                        end if;

                  end if;

                end if;

                -- Latches the signals

                NUMBER0 <= NUMBER0_sig;

                NUMBER1 <= NUMBER1_sig;

                NUMBER2 <= NUMBER2_sig;

                NUMBER3 <= NUMBER3_sig;

                NUMBER4 <= NUMBER4_sig;

                NUMBER5 <= NUMBER5_sig;

                NUMBER6 <= NUMBER6_sig;

                NUMBER7 <= NUMBER7_sig;

                LEDR(15 downto 0) <= LEDR_sig;

                LEDG(7 downto 0) <= LEDG_sig;

        end process;

        -- the following three processes deals with different clock domain signals

        ps2_process1: process(CLOCK_50)