Subversion Repositories z80control

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

-- Z80 Control Microprocessor

--

-- Version history:

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

-- Version 0.2 Alpha for for Altera DE1

-- Developer: Tyler Pohl

-- Release Date: 2010 / 10 / 01

--

-- 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):

--

--      40 KB Internal ROM              Read            (0x0000h - 0x9FFFh) -- Location 1FFFH will be used to unlock locked RAM in future

--

--  08 KB Shared Memory     Read/Write  (0xA000h - 0xBFFFh)

--

--        Locked Supr1                  (0xC000h - 0xC7FFh)

--                Supr2                                     (0xC800h - 0xCFFFh) 

--        Supr3                         (0xD000h - 0xD7FFh) 

--        Supr4                         (0xD800h - 0xDFFFh) -- Stack starts at DFEA and goes down initialize this in z80 code

--        Supr5                         (0xE000h - 0xE7FFh) 

--        Supr6                                                 (0xE800h - 0xEFFFh) 

--        Lacoked Pram                                  (0xF000h - 0xF7FFh) -- Switched between 5 banks

--        Sram                          (0xF800h - 0xF8FFh) -- Switched between 5 banks

--                Ram                           (0xF900h - 0xFFFFh) -- Switched between 5 banks

--      08 Green Leds                   Out                     (Port 0x01h)

--      08 Red Leds                             Out                     (Port 0x02h)

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

--  01 Uart0                            In/Out          (Port 0x24h)

--  01 Rom Switching        Out         (Port 0xDDh)

--  02 Rom Switching        Out         (Port 0xDDh)

--  03 Rom Switching        Out         (Port 0xDDh)

--  00 to 04 Ram Bank Switching  Out         (Port 0xDCh)

-- Future Ports (Registers)

--PRF F0h

--STATS,RTCIN F0h       --Brown Out and Pwr Fail Stat 60Hz

--PFKILL F1h

--RTCRST F2h

--SFTPRT F3h

--MEXPON F4h

--MEXPOFF F5h

--IOXPON F6h

--IOXPOFF F7h

--EPPAGE1 FCh

--EPPAGE2 FDh

--

--  Revision history:

--

-- 2010/10/01 - Modified RAM layout to support new and future improvements

--            - Changed ROM to support 16 bit addresses

--                        - Serial port Recived works under Interrupt -- Load z80test and data ends up on hex display   

--

--

-- Getting Started

        -- Use CII_Starter_USB_API_v1 project to load flash chip - don't forget to erase chip first

        -- Load rom.bin to flash chip starting at address 0

        -- Connect the serial port up to hyperterminal or minicom

        -- Sends data out serial port and displays on hex display data sent

        -- Type chars to send from PC serial port - z80 recieves and displays on hex display under interrupt

--

--

-- TO-DO:

-- - MOST IMPORTANT !!!! - This is halting my progress

-- - Search for this ????? and figure out why it stops the CPU from running 

-- -

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

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

-- - Get Flash Write to Work -- Why does the CPU not run when connecting DO_CPU to the FL_DQ pins ?

-- - Figure out why cpu does not run when having LED, and uart enabled in the Port output section

-- - Get all the memory above working and document.

-- - Get the serial Tx Interrupt to work.

-- - Add registers to uart so baudrate, parity, interrupts can be modified.

-- - Document this project in the form of Microprocessor Datasheets.

-- - Design Template of Software to communicate to the Board

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

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 : out std_logic;                                         -- Write Enable

    FL_RST_N : out std_logic;                                        -- Reset

    FL_OE_N : out std_logic;                                         -- 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

        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 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;

                clock_10sec             : OUT   STD_LOGIC;

                clock_1min              : OUT   STD_LOGIC;

                clock_1hr               : 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 miniUART

        PORT (

                SysClk   : in  Std_Logic;  -- System Clock

                Reset    : in  Std_Logic;  -- Reset input

                CS_N     : in  Std_Logic;

                RD_N     : in  Std_Logic;

                WR_N     : in  Std_Logic;

                RxD      : in  Std_Logic;

                TxD      : out Std_Logic;

                IntRx_N  : out Std_Logic;  -- Receive interrupt

                IntTx_N  : out Std_Logic;  -- Transmit interrupt

                Addr     : in  Std_Logic_Vector(1 downto 0); -- 

                DataIn   : in  Std_Logic_Vector(7 downto 0); -- 

                DataOut  : out Std_Logic_Vector(7 downto 0)); --     

        END COMPONENT;

        signal INT_n    : std_logic;

        signal M1_n             : std_logic;

        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 Clk_357Mhz       : 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 AA               : std_logic_vector(21 downto 0);

        signal D_ROM    : std_logic_vector(7 downto 0);

        signal clk25mhz         : std_logic;

        signal clk1hz           : std_logic;

        signal clk10hz          : std_logic;

        signal clk100hz         : std_logic;

        signal clk10sec         : std_logic;

        --signal clk1min                : std_logic;

        --signal clk1hr         : 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 uart0_CS                 : std_Logic;

        signal uart0_RD                 : std_Logic;

        signal uart0_WR                 : std_Logic;

        signal uart0_RxInt              : std_Logic;

        signal uart0_TxInt              : std_Logic;

        signal uart0_Addr       : std_Logic_Vector(1 downto 0);

        signal uart0_DataIn     : std_Logic_Vector(7 downto 0);

        signal uart0_DataOut    : std_logic_Vector(7 downto 0);

        signal UartIntVector    : std_logic_Vector(7 downto 0);

        signal IntVector                : std_logic_Vector(7 downto 0);

        signal LEDRED           : std_logic_Vector(7 downto 0);

begin

        Rst_n_s <= not SW(9);                   -- Switch 9 toggles Reset on z80

        HEX0 <= HEX_DISP0;                              -- Move Signal to Output Pins

        HEX1 <= HEX_DISP1;                              -- Move Signal to Output Pins

        HEX2 <= HEX_DISP2;                              -- Move Signal to Output Pins   

        HEX3 <= HEX_DISP3;                              -- Move Signal to Output Pins

        -- SRAM control signals

        SRAM_ADDR(15 downto 0) <= A - x"C000" when (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"C000") else (others => 'Z');

        SRAM_WE_N <= Wr_n or MREQ_n when A >= x"C000";

        SRAM_OE_N <= Rd_n or MREQ_n when A >= x"C000";  --Rd_n;

        -- ???? Why can't this pin be connected to MREQ_n CPU will not run unless its is connected to zero

        SRAM_CE_N <= '0';

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

        --1FFFH is used for unlocking ram in future.  Auto lock after one read or write.

        -- FLASH control signals        

        --FL_ADDR(15 downto 0) <= A(15 downto 0) when (Clk_Z80 = '1' and A < x"A000");

        FL_ADDR(15 downto 0) <= A(15 downto 0) when (A < x"A000" and MREQ_n = '0');

    --D_ROM(7 downto 0) <=  FL_DQ when (Clk_Z80 = '1' and A < x"A000");

        D_ROM(7 downto 0) <=  FL_DQ when (A < x"A000" and MREQ_n = '0');

    -- ????? Unblock this and CPU will not run

    --FL_DQ <= DO_CPU when (Wr_n = '0' and MREQ_n = '0' and A < x"A000") else (others => 'Z');

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

    FL_DQ       <= (others => 'Z');

    FL_WE_N <= '1';              --'1';                 -- Write Enable

    FL_OE_N <= Rd_n;    -- Output Enable

    FL_CE_N <= MREQ_n when A < x"A000"; -- Chip Enable

    --Buffer Flash Data Lines

        --D_ROM(0) <= '1' when FL_DQ(0) = '1' else '0';

        --D_ROM(1) <= '1' when FL_DQ(1) = '1' else '0';

        --D_ROM(2) <= '1' when FL_DQ(2) = '1' else '0';

        --D_ROM(3) <= '1' when FL_DQ(3) = '1' else '0';

        --D_ROM(4) <= '1' when FL_DQ(4) = '1' else '0';

        --D_ROM(5) <= '1' when FL_DQ(5) = '1' else '0';

        --D_ROM(6) <= '1' when FL_DQ(6) = '1' else '0';

        --D_ROM(7) <= '1' when FL_DQ(7) = '1' else '0'; 

        -- UART control signals

        uart0_CS <= IORQ_n when (A(7 downto 0) = x"24" and IORQ_n = '0');

        uart0_RD <= Rd_n when (A(7 downto 0) = x"24" and IORQ_n = '0');

        uart0_WR <= Wr_n when (A(7 downto 0) = x"24" and IORQ_n = '0');

        uart0_Addr <= b"00";

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

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

        --Z80 Interrupt Vectors

        --               IBMVECT

        --0040 AA1C               DW        COMMBOUT    ;CHAN-B TRANSMIT BUFFER EMPTY

        --0042 101B               DW        COMBCLI     ;BSTATUS

        --0044 F21C               DW        COMMBIN     ;BRECEIVE

        --0046 FF1A               DW        COMBCLII    ;BEXTINT

        --0048 281C               DW        COMMAOUT    ;ATRBMTY

        --004A 691C               DW        COMACLI     ;WAS CRTEXINT   ;ASTATUS

        --004C 2F1B               DW        COMMAIN     ;WAS CRTINP     ;ARECEIVE

        --004E 971C               DW        COMACLII    ;WAS CRTEXIN?   ;AEXTINT        

        IntVector(7 downto 0) <= x"4C"  when (IORQ_n = '0' and MREQ_n = '1' and M1_n = '0' and uart0_RxInt = '1');

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

        -- Depending on bus signals DI_CPU gets loaded with one of these values.  

        -- Note: bus signals change while z80 is executing different instructions.

        -- Input to Z80

        DI_CPU <=

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

                        --Input ROM Code

                        D_ROM when (Rd_n = '0' and MREQ_n = '0' and IORQ_n = '1' and A < x"A000") else

                        uart0_DataIn(7 downto 0) when (IORQ_n = '0' and MREQ_n = '1' and Rd_n = '0' and A(7 downto 0) = x"24") else

                        IntVector(7 downto 0) when (IORQ_n = '0' and MREQ_n = '1' and M1_n = '0' and uart0_RxInt = '1') 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 uart0_buf_DataOut: std_logic_vector(7 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

                        -- 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

                                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);

                        elsif A(7 downto 0) = x"24" then

                                uart0_buf_DataOut := DO_CPU;            --load data to uart output buffer

                        end if;

                  end if;

                end if;

                -- Latches the signals

                NUMBER0 <= NUMBER0_sig;

                NUMBER1 <= NUMBER1_sig;

                NUMBER2 <= NUMBER2_sig;

                NUMBER3 <= NUMBER3_sig;

                -- ???? Unblock this and CPU will not run

                -- NOTE it will work if you block uart0_DataOut below

                --LEDRED(7 downto 0) <= LEDR_sig(7 downto 0);

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

                uart0_DataOut <= uart0_buf_DataOut;

        end process;

        One <= '1';

        z80_inst: T80se

                port map (

                        M1_n => M1_n,

                        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 => INT_n,

                        NMI_n => clk1hz,

                        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

                );

        clkdiv_inst: clk_div

        port map (

                clock_25Mhz                             => CLOCK_27,

                clock_1MHz                              => open,

                clock_100KHz                    => open,

                clock_10KHz                             => open,

                clock_1KHz                              => open,

                clock_100Hz                             => clk100hz,

                clock_10Hz                              => clk10hz,

                clock_1Hz                               => clk1hz,

                clock_10sec                             => clk10sec,

                clock_1min                              => open,

                clock_1hr                               => open

        );

        clock_z80_inst : Clock_357Mhz

                port map (

                        clock_50Mhz             => CLOCK_50,

                        clock_357Mhz    => Clk_Z80

        );

        DISPHEX0 : decoder_7seg PORT MAP (

                NUMBER                  =>      NUMBER0,

                HEX_DISP                =>      HEX_DISP0

        );

        DISPHEX1 : decoder_7seg PORT MAP (

                NUMBER                  =>      NUMBER1,

                HEX_DISP                =>      HEX_DISP1

        );

        DISPHEX2 : decoder_7seg PORT MAP (

                NUMBER                  =>      NUMBER2,

                HEX_DISP                =>      HEX_DISP2

        );

        DISPHEX3 : decoder_7seg PORT MAP (

                NUMBER                  =>      NUMBER3,

                HEX_DISP                =>      HEX_DISP3

        );

        U1 : miniUART PORT MAP (

                SysClk   => CLOCK_50,           --: in  Std_Logic;  -- System Clock

                Reset    => Key(0),              --: in  Std_Logic;  -- Reset input

                CS_N     => uart0_cs,           --: in  Std_Logic;

                RD_N     => uart0_Rd,           --: in  Std_Logic;

                WR_N     => uart0_Wr,           --: in  Std_Logic;

                RxD      => UART_RXD,           --: in  Std_Logic;

                TxD      => UART_TXD,           --: out Std_Logic;

                IntRx_N  => uart0_RxInt,                --: out Std_Logic;  -- Received Byte

                IntTx_N  => uart0_TxInt,                --: out Std_Logic;  -- Transmit Buffer Empty

                Addr     => uart0_Addr,         --: in  Std_Logic_Vector(1 downto 0); -- 

                DataIn   => uart0_DataOut,      --: in  Std_Logic_Vector(7 downto 0); -- 

                DataOut  => uart0_DataIn        --: out Std_Logic_Vector(7 downto 0)); --                               

        );

        LEDR(0) <= '1' when LEDRED(0) = '1' else '0';

        LEDR(1) <= '1' when LEDRED(1) = '1' else '0';

        LEDR(2) <= '1' when LEDRED(2) = '1' else '0';

        LEDR(3) <= '1' when LEDRED(3) = '1' else '0';

        LEDR(4) <= '1' when LEDRED(4) = '1' else '0';

        LEDR(5) <= '1' when LEDRED(5) = '1' else '0';

        LEDR(6) <= '1' when LEDRED(6) = '1' else '0';

        LEDR(7) <= '1' when LEDRED(7) = '1' else '0';

        INT_n <= '0' when uart0_RxInt ='1' else '1';

    -- Block any of these and CPU will not run -- ?????

        LEDG(0) <= uart0_RxInt;

        LEDG(1) <= uart0_TxInt;

        LEDG(5) <= INT_n;

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

        LEDG(6) <= clk10sec;

        LEDG(7) <= clk1hz;

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

        SRAM_ADDR(17 downto 16) <= "00";

        SRAM_UB_N <= '1';

        SRAM_LB_N <= '0';

        SRAM_CE_N <= '0';

        --

        UART_TXD <= 'Z';

        DRAM_ADDR <= (others => '0');

        DRAM_LDQM <= '0';

        DRAM_UDQM <= '0';

        DRAM_WE_N <= '1';

        DRAM_CAS_N <= '1';

        DRAM_RAS_N <= '1';

        DRAM_CS_N <= '1';

        DRAM_BA_0 <= '0';

        DRAM_BA_1 <= '0';

        DRAM_CLK <= '0';

        DRAM_CKE <= '0';

    FL_ADDR(21 downto 16) <= b"000000";

    FL_RST_N <= '1';            -- Reset

        TDO <= '0';

        I2C_SCLK <= '0';

        AUD_DACDAT <= '0';

        AUD_XCK <= '0';

        -- Set all bidirectional ports to tri-state

        DRAM_DQ     <= (others => 'Z');

        I2C_SDAT    <= 'Z';

        AUD_ADCLRCK <= 'Z';

        AUD_DACLRCK <= 'Z';

        AUD_BCLK    <= 'Z';

        GPIO_0 <= (others => 'Z');

        GPIO_1 <= (others => 'Z');

end;