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-- Z80_Soc (Z80 System on Chip)

--

-- Version history:

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

-- 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;

entity  TOP_DE1 is

        port(

    -- Clocks

    CLOCK_27,                                      -- 27 MHz

    CLOCK_50,                                      -- 50 MHz

    EXT_CLOCK : in std_logic;                      -- External Clock

    -- Buttons and switches

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

    SW : in std_logic_vector(9 downto 0);          -- Switches

    -- LED displays

    HEX0, HEX1, HEX2, HEX3                         -- 7-segment displays

                        : out std_logic_vector(6 downto 0);

    LEDG : out std_logic_vector(7 downto 0);       -- Green LEDs

    LEDR : out std_logic_vector(9 downto 0);       -- Red LEDs

    -- RS-232 interface

    UART_TXD : out std_logic;                      -- UART transmitter   

    UART_RXD : in std_logic;                       -- UART receiver

    -- IRDA interface

    -- IRDA_TXD : out std_logic;                      -- IRDA Transmitter

    IRDA_RXD : in std_logic;                       -- IRDA Receiver

    -- SDRAM

    DRAM_DQ : inout std_logic_vector(15 downto 0); -- Data Bus

    DRAM_ADDR : out std_logic_vector(11 downto 0); -- Address Bus    

    DRAM_LDQM,                                     -- Low-byte Data Mask 

    DRAM_UDQM,                                     -- High-byte Data Mask

    DRAM_WE_N,                                     -- Write Enable

    DRAM_CAS_N,                                    -- Column Address Strobe

    DRAM_RAS_N,                                    -- Row Address Strobe

    DRAM_CS_N,                                     -- Chip Select

    DRAM_BA_0,                                     -- Bank Address 0

    DRAM_BA_1,                                     -- Bank Address 0

    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(21 downto 0);     -- Address bus

    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(17 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_DAT : in std_logic;      -- SD Card Data      SD pin 7 "DAT 0/DataOut"

    SD_DAT3 : out std_logic;    -- SD Card Data 3    SD pin 1 "DAT 3/nCS"

    SD_CMD : out std_logic;     -- SD Card Command   SD pin 2 "CMD/DataIn"

    SD_CLK : out std_logic;     -- SD Card Clock     SD pin 5 "CLK"

    -- USB JTAG link

    TDI,                        -- CPLD -> FPGA (data in)

    TCK,                        -- CPLD -> FPGA (clk)

    TCS : in std_logic;         -- CPLD -> FPGA (CS)

    TDO : out std_logic;        -- FPGA -> CPLD (data out)

    -- I2C bus

    I2C_SDAT : inout std_logic; -- I2C Data

    I2C_SCLK : out std_logic;   -- I2C Clock

    -- PS/2 port

    PS2_DAT,                    -- Data

    PS2_CLK : inout std_logic;     -- Clock

    -- VGA output

    VGA_HS,                                             -- H_SYNC

    VGA_VS : out std_logic;                             -- SYNC

    VGA_R,                                              -- Red[3:0]

    VGA_G,                                              -- Green[3:0]

    VGA_B : out std_logic_vector(3 downto 0);           -- Blue[3:0]

    -- 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

    -- General-purpose I/O

    GPIO_0,                                      -- GPIO Connection 0

    GPIO_1 : inout std_logic_vector(35 downto 0) -- GPIO Connection 1    

);

end TOP_DE1;

architecture rtl of TOP_DE1 is

        use work.z80soc_pack.all;

        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 => Single 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 (

                Clk     : in std_logic;

                A       : in std_logic_vector(11 downto 0);

                D       : out std_logic_vector(7 downto 0));

        end component;

        component Clock_357Mhz

        PORT (

                clock_50Mhz                             : IN    STD_LOGIC;

                clock_357Mhz                    : OUT   STD_LOGIC);

        end component;

        component clk_div

        PORT

        (

                clock_25Mhz                             : IN    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 vram3200x8

        port

        (

                rdaddress               : IN STD_LOGIC_VECTOR (11 DOWNTO 0);

                wraddress               : IN STD_LOGIC_VECTOR (11 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 charram2k

        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(12 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 video_PLL

        PORT

        (

                inclk0          : IN STD_LOGIC  := '0';

                c0                      : 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 clk25mhz         : std_logic;

        signal clk100hz         : std_logic;

        signal clk10hz          : std_logic;

        signal clk1hz           : 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 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 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(12 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 VID_CURSOR               : std_logic_vector(15 downto 0);

        signal CURSOR_X             : std_logic_vector(6 downto 0);

        signal CURSOR_Y             : std_logic_vector(5 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);

        signal Z80SOC_VERSION           : std_logic_vector(2 downto 0);   -- "000" = DE1, "001" = S3E

begin

        Z80SOC_VERSION <= "000";                -- "000" = DE1, "001" = S3E

        Rst_n_s <= not SW(9);

        HEX0 <= HEX_DISP0;

        HEX1 <= HEX_DISP1;

        HEX2 <= HEX_DISP2;

        HEX3 <= HEX_DISP3;

--      Write into VRAM

        vram_addra <= VID_CURSOR when (IORQ_n = '0' and MREQ_n = '1' and A(7 downto 0) = x"90")  else

                      A - x"4000" when (A >= x"4000" and A < x"4C80");

        vram_wea   <= '0' when ((A >= x"4000" and A < x"4C80" and Wr_n = '0' and MReq_n = '0') or (Wr_n = '0' and IORQ_n = '0' and A(7 downto 0) = x"90")) else

                '1';

        vram_dina <= DO_CPU;

-- Write into char ram

        cram_addra      <= A - x"4C80";

        cram_dina       <= DO_CPU;

        cram_wea        <= '0' when (A >= x"4C80" and A < x"5480" and Wr_n = '0' and MReq_n = '0') else '1';

        -- 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 onthis platform

        SRAM_ADDR(15 downto 0) <= A - x"4000" when (A >= x"4000"  and A < x"C000" and MREQ_n = '0');

        SRAM_DQ(7 downto 0) <= DO_CPU when (Wr_n = '0' and MREQ_n = '0' and A >= x"4000"  and A < x"C000") else (others => 'Z');

        SRAM_WE_N <= Wr_n or MREQ_n when (A >= x"4000" and A < x"C000");

        SRAM_OE_N <= Rd_n;

        -- Input to Z80

        DI_CPU <= ("00000" & Z80SOC_VERSION) when (Rd_n = '0' and MREQ_n = '0' and A = x"FFDF") else

                        D_ROM when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A < x"4000") else

                        --vram_douta when (MREQ_n = '0' and IORQ_n = '1' and Rd_n = '0' and A < x"4C80") else

                        --cram_douta when (MREQ_n = '0' and IORQ_n = '1' and Rd_n = '0' and A < x"5480") else

                        SRAM_DQ(7 downto 0) when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A >= x"4000" and A < x"C000") 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

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

                        GPIO_0(7 downto 0) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"A0") else

                        GPIO_0(15 downto 8) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"A1") else

                        GPIO_0(23 downto 16) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"A2") else

                        GPIO_0(31 downto 24) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"A3") else

                        ("0000" & GPIO_0(35 downto 32)) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"A4") else

                        GPIO_1(7 downto 0) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"B0") else

                        GPIO_1(15 downto 8) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"B1") else

                        GPIO_1(23 downto 16) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"B2") else

                        GPIO_1(31 downto 24) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"B3") else

                        ("0000" & GPIO_1(35 downto 32)) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"B4") else

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

                        ("0" & CURSOR_X) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"91") else

                        ("00" & CURSOR_Y) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"92") 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 LEDG_sig               : std_logic_vector(7 downto 0);

        variable LEDR_sig               : std_logic_vector(9 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;

                        -- HEX1 and HEX0

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

                                NUMBER2_sig := DO_CPU(3 downto 0);

                                NUMBER3_sig := DO_CPU(7 downto 4);

                        -- HEX3 and HEX2

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

                                NUMBER0_sig := DO_CPU(3 downto 0);

                                NUMBER1_sig := DO_CPU(7 downto 4);

                        -- GPIO_0

                        elsif A(7 downto 0) = x"A0" then

                                GPIO_0_buf_out(7 downto 0)   := DO_CPU;

                        elsif A(7 downto 0) = x"A1" then

                                GPIO_0_buf_out(15 downto 8)  := DO_CPU;

                        elsif A(7 downto 0) = x"A2" then

                                GPIO_0_buf_out(23 downto 16) := DO_CPU;

                        elsif A(7 downto 0) = x"A3" then

                                GPIO_0_buf_out(31 downto 24) := DO_CPU;

                        elsif A(7 downto 0) = x"A4" then

                                GPIO_0_buf_out(35 downto 32) := DO_CPU(3 downto 0);

                        -- GPIO_1

                        elsif A(7 downto 0) = x"B0" then

                                GPIO_1_buf_out(7 downto 0)   := DO_CPU;

                        elsif A(7 downto 0) = x"B1" then

                                GPIO_1_buf_out(15 downto 8)  := DO_CPU;

                        elsif A(7 downto 0) = x"B2" then

                                GPIO_1_buf_out(23 downto 16) := DO_CPU;

                        elsif A(7 downto 0) = x"B3" then

                                GPIO_1_buf_out(31 downto 24) := DO_CPU;

                        elsif A(7 downto 0) = x"B4" then

                                GPIO_1_buf_out(35 downto 32) := DO_CPU(3 downto 0);

                        elsif A(7 downto 0) = x"C0" then

                                GPIO_0 <= GPIO_0_buf_out;

                        elsif A(7 downto 0) = x"C1" then

                                GPIO_1 <= GPIO_1_buf_out;

                        end if;

                  end if;

                end if;

                -- Latches the signals

                NUMBER0 <= NUMBER0_sig;

                NUMBER1 <= NUMBER1_sig;

                NUMBER2 <= NUMBER2_sig;

                NUMBER3 <= NUMBER3_sig;

                LEDR(7 downto 0) <= LEDR_sig(7 downto 0);

                LEDG <= LEDG_sig;

        end process;

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

        ps2_process1: process(CLOCK_50)

        begin

                if CLOCK_50'event and CLOCK_50 = '1' then

                        if ps2_read = '1' then

                                if ps2_ascii_sig /= x"FF" then

                                        ps2_read <= '0';

                                        ps2_ascii_reg1 <= "00000000";

                                end if;

                        elsif ps2_scan_ready = '1' then

                                if ps2_ascii_sig = x"FF" then

                                        ps2_read <= '1';

                                else

                                        ps2_ascii_reg1 <= ps2_ascii_sig;

                                end if;

                        end if;

                end if;

        end process;

        ps2_process2: process(Clk_Z80)

        begin

                if Clk_Z80'event and Clk_Z80 = '1' then

                        ps2_ascii_reg <= ps2_ascii_reg1;

                end if;

        end process;

        cursorxy: process (Clk_Z80)

        variable VID_X  : std_logic_vector(6 downto 0);

        variable VID_Y  : std_logic_vector(5 downto 0);

        begin

                if Clk_Z80'event and Clk_Z80 = '1' then

                        if (IORQ_n = '0' and MREQ_n = '1' and Wr_n = '0' and A(7 downto 0) = x"91") then

                                VID_X := DO_CPU(6 downto 0);

                        elsif (IORQ_n = '0' and MREQ_n = '1' and Wr_n = '0' and A(7 downto 0) = x"92") then

                                VID_Y := DO_CPU(5 downto 0);

                        elsif (IORQ_n = '0' and MREQ_n = '1' and Wr_n = '0' and A(7 downto 0) = x"90") then

                                if VID_X = vid_cols - 1 then

                                        VID_X := "0000000";

                                        if VID_Y = vid_lines - 1 then

                                                VID_Y := "000000";

                                        else

                                                VID_Y := VID_Y + 1;

                                        end if;

                                else

                                        VID_X := VID_X + 1;

                                end if;

                        end if;

                end if;

                VID_CURSOR <= vram_base_addr + ( VID_X + ( VID_Y * conv_std_logic_vector(vid_cols,7)));

                CURSOR_X <= VID_X;

                CURSOR_Y <= VID_Y;

        end process;

        One <= '1';

        z80_inst: T80se

                port map (

                        M1_n => open,

                        MREQ_n => MREQ_n,

                        IORQ_n => IORQ_n,

                        RD_n => Rd_n,

                        WR_n => Wr_n,

                        RFSH_n => open,

                        HALT_n => open,

                        WAIT_n => One,

                        INT_n => One,

                        NMI_n => One,

                        RESET_n => Rst_n_s,

                        BUSRQ_n => One,

                        BUSAK_n => open,

                        CLK_n => Clk_Z80,

                        CLKEN => One,

                        A => A,

                        DI => DI_CPU,

                        DO => DO_CPU

                );

        video_inst: video port map (

                        CLOCK_25                => clk25mhz,

                        VRAM_DATA               => vram_doutb,

                        VRAM_ADDR               => vram_addrb(12 downto 0),

                        VRAM_CLOCK              => vram_clkb,

                        VRAM_WREN               => vram_web,

                        CRAM_DATA               => cram_doutb,

                        CRAM_ADDR               => cram_addrb(10 downto 0),

                        CRAM_WEB                => cram_web,

                        VGA_R                   => VGA_R,

                        VGA_G                   => VGA_G,

                        VGA_B                   => VGA_B,

                        VGA_HS                  => VGA_HS,

                        VGA_VS                  => VGA_VS

        );

        vram : vram3200x8

                port map (

                rdclock         => vram_clkb,

                wrclock         => Clk_Z80,

                wren            => not vram_wea, -- inverted logic so code is similar to SRAM and S3E port

                wraddress       => vram_addra(11 downto 0),