path: root/instructions.txt

                                      DS81
                ---------==============================---------

                           Copyright 2006 Ian Cowburn
                              ianc@noddybox.co.uk


1. LICENSE
----------

    The code to DS81 is released under the GNU General Public License.  See
    the text file COPYING for details.

    Other included software is provided in good faith, is not released under
    the GNU General Public License, and is copyright their respective authors.
    If any of these authors disagree with the distribution of their work then
    contact me and it will be gladly removed.

        ZX81 BASIC ROM (c) 1981 Nine Tiles Networks LTD
        3D Monster Maze (c) 1983 Malcolm E. Evans
        Mazogs, City Patrol and Sabotage (c) 1981, 1982 Don Priestley


2. ZX81
-------

    The ZX81 was an 8-bit computer released by Sinclair Research in 1981, using
    the Z80 CPU.
    
    It was a monochrome machine with no sound (be quiet those at the back of
    the room who used to be able to do sound by doing odd things with the video
    signal) and a text mode that could be used to plot graphics at a resolution
    of 64 by 44 (hmmm, smaller than most icons nowadays).

    It came with 1K of RAM, though most people opted for a massive 16K RAM pack.


2. DS81
-------

    DS81 is an emulation of the 16K ZX81 and is is supplied in two main forms,
    as a native Nintendo DS executable and a version with a Gameboy Advance
    wrapper (in case your Ninentdo DS homebrew device only supports running
    GBA executables).
    
    In addition to this two different versions are supplied, one which
    initialises the FAT library and one which doesn't.  They are identical save
    for this, and separate ones are supplied in case the FAT library
    initialisation causes problem on your homebrew device:

        ds81.nds          - Nintendo DS version
        ds81.ds.gba       - As above with a GBA wrapper.

        ds81-nofat.nds    - Nintendo DS version; no FAT library initialisation.
        ds81-nofat.ds.gba - As above with a GBA wrapper.

    I'm probably being overly paranoid there, but better safe than sorry.

    In any of the following sections where files are mentioned it obviously
    doesn't apply to the 'nofat' versions.


3. Using DS81
-------------

    When run DS81 displays a splash screen with copyright information and
    whether the FAT library has been able to find a supported device for the
    loading of external tapes.

    Once the A button has been pressed the ZX81 resets and displays itself
    on the top screen, and a soft keyboard is displayed on the bottom, touch
    sensitive, DS screen.

    Also at this point, if so configured, a default memory snap will be loaded.
    See the "Memory Snapshots" section for more details.
    
    If you've never used a ZX81 before then you may wish to find out how the
    keyboard works -- it uses a keyword entry system, rather than the straight
    typing if commands.  So, for instance, the key P is pressed to enter PRINT
    when the cursor is in keyword mode (the cursor in an inverted K).

    Trust me; you were glad of it when using the original ZX81's hard plastic
    membrane keyboard.

    When using the soft keyboard by default the shift key is 'sticky' and once
    used will stay held down until pressed again.

    The World of Spectrum has the original ZX81 manuals, either as a PDF
    or in HTML form:

        http://www.worldofspectrum.org/

    At the bottom of the keyboard is an area where you can click to bring up a
    menu.  Either use the stylus, or the joypad and button A to select an
    option from the following choices:

        RESET ZX81     
            This resets the emulated ZX81.

        SELECT TAPE     
            Selects the built-in tape to use (DS81 has a number of ZX81 tapes
            built into it).  The next section has extra information on the
            loading of games.

        CONFIGURE
            Lets you configure settings (see last section for settings).
            
            If you press SELECT to exit the configuration screen then the
            configuration is saved into the file /DS81.CFG which is read on
            start-up.

        MAP JOYPAD TO KEYS
            Allows you to redefine the DS's joypad and buttons to ZX81 keys.
            Follow the on-screen instructions.

        MACHINE CODE MONITOR
            Provides access to a basic machine code/memory monitor.  This lets 
            you watch the ZX81 execute op-codes, or single-step over them.

            Unless you're actually interested in such things you'll never need
            to go near this option -- it's there to track down emulation bugs
            as much as anything.

            See the second to last section for more details.

        SAVE MEMORY SNAPSHOT
            Saves a memory snapshot.  This option only works if a FAT-enabled
            version of DS81 is being used.  See the "Memory Snapshot" section
            for more details.

        LOAD MEMORY SNAPSHOT
            Loads a memory snapshot.  This option only works if a FAT-enabled
            version of DS81 is being used.  See the "Memory Snapshot" section
            for more details.

        SAVE JOYPAD/KEY STATE
            Saves a snapshot that just contains the current state of the
            keyboard and the joypad mappings.  This just allows you to save
            a complex controller mapping to share between different games.

        LOAD JOYPAD/KEY STATE
            This loads the state of the keyboard and the joypad mappings
            from a selected file.

        CANCEL
            Cancels the menu.



4. Using the internal tapes on DS81
-----------------------------------

    Games on the ZX81 were supplied on cassette.  DS81 includes a few tape
    files that are selectable from the menu.  Follow the on-screen instructions
    to select the game.  A quick description and the controls to use are
    displayed on the top screen.

    Once you've selected a tape you can load it in the emulator by using the
    command LOAD "".  If you're really stuck with the ZX81 keyboard:

        1. Select your tape.
        2. Reset the ZX81 from the menu.
        3. When the inverse K cursor is displayed press the J key to generate
           the keyword LOAD.
        4. Press the SHIFT key.
        5. Press the P key twice to enter the double quotes (DON'T use the
           double quotes got by pressing SHIFT+Q.  These are not the same!)
        6. Release the SHIFT key and press the NEW LINE key.
        7. The tape will load and run.


5. Using external tapes on DS81
-------------------------------

    If you are using the version of DS81 that allows the use of FAT devices,
    and you device is supported, they you can load any old tape.

    FAT support is via the new DLDI interface, so you may need to dynamically
    link in the appropriate FAT driver.  Details are available here:

        http://chishm.drunkencoders.com/DLDI/index.html

    Note that the default driver linked in is the Datel Max Media Dock
    (Compact Flash) -- solely as that's what I have.

    Simply place the .P file (ZX81 games are usually distributed as .P files
    that are simply an image of the memory that would have been dumped to tape)
    and either put it in the root directory of the FAT device or in a directory
    called ZX81SNAP.

    Alternatively if you can't remember the names of files, loading "*" will
    give you with a file selector to select the tape file with.

    It can't be at all guaranteed that all original ZX81 games will work as
    expected.  After all, DS81 isn't really a ZX81.


6. High Resolution Support
--------------------------

    There is now some support for high-resolution ZX81 games.  Currently
    it doesn't run quite full speed, and it won't work if the routines are
    too clever - unfortunately, like Manic Miner where it switches between
    high and low-resolution in the same frame.

    I know the Software Farms games seem to work, though "Forty Niner"
    sometimes goes mad (just incrementing the score) though that's probably
    a general emulation bug.  Of course unless it did that anyway -- I've never
    played it before.
    
    Steven McDonald's games seem to cause no-problem so far.

    If a game doesn't look right it may also be worth enabling the 'RAM AT 8192'
    option.

    If you know of a game that seems to cause it real trouble, please let me
    know -- the high-resolution support is still a bit of a hack whereby the
    emulator searches memory for the display file on detecting that the 'I'
    register has changed.


7. Machine Code Monitor
-----------------------

    On starting the machine code monitor the keyboard will go dim and get
    overlaid with a text display showing you the Z80 instructions about to be
    executed along with the current states of the registers in the Z80.

    The keyboard is dim, but still on display as the montitor does let you
    use the keyboard.  Note that all keys are sticky (like the shift key in its
    default state) and that joypad mappings are ignored.

    With the monitor on display the following joypad keys can be used:

    START       - Toggles between running continuously and single-step mode.

    A           - If in single-step mode then executes the next instruction.

    X           - Display a help page.

    SELECT      - Toggles between the current disassembly/CPU state display,
                  a disassembly or a hex-dump of memory.

    L/R         - The shoulder buttons change the address being displayed on
                  the memory dump.  Hold the Y key at the same time to make
                  it jump in bigger steps.

    B           - Cycles the value used for the memory dump or assembly views;
                  either the address as set with the shoulder buttons, or one
                  of the registers: HL, IX, SP, IY, BC, DE or PC.

    Press the config bar at the bottom of the soft keyboard to exit the
    machine code monitor and return to normal running.


8. Configuration Options
------------------------

    STICKY SHIFT

        This option allows you to decide whether the shift key on the soft
        keyboard is sticky (toggles when you press it) or acts like the other
        keys.  You should never need to make it non-sticky unless a game needs
        it.

    AVERAGE TOUCHSCREEN

        This option can be enabled if your touch-screen seems to suffer from
        jumps (mine seems to once in a while) and causes the soft keyboard to
        only register touchscreen presses if they are within 5 pixels of each
        other over two frames.  Your mileage my vary, but for me it stops the
        menu randomly appearing.

        This means that response can be reduced by a frame, but it shouldn't
        cause problems.

    RAM AT 8192

        One hardware fix that could be made to the ZX81 was to replace the
        mirror of the ROM that started at 8192 with RAM.  This allowed
        true high resolution graphics.
        
        Not that I've found any that work yet :-)

    ALLOW TAPE SAVE

        If enabled this means that files saved with the SAVE command will
        try and create a .P file in the ZX81SNAP directory, or the root
        directory.  You can SAVE "*" to bring up the file selector.

        If not enabled attempts to SAVE files from BASIC will be silently
        ignored.

    LOAD DEFAULT MEMORY SNAP

        If enabled DS81 will look for a memory snapshot called AUTO.D81 in 
        either the root directory or the ZX81SNAP directory.
        
        See the "Memory Snapshot" section for more details on snapshots.


9. Memory Snapshots
-------------------

    Since version 1.3 DS81 now supports basic memory snapshots.  When you
    select the "SAVE MEMORY SNAPSHOT" from the main menu DS81 will prompt
    for a filename (only up to 8 alphabetical characters).  Once entered
    the snapshot will be saved in the directory ZX81SNAP with an automatically
    added .D81 extension.  If this save fails, an attempt is made to save the
    snapshot in the root directory of the device.

    On selecting to load a memory snapshot a file selector is displayed.  On
    selecting one of the snapshots it will be instantly loaded.

    Note that along with the machine's state the currently configured keypad
    mappings are saved in the snapshot and restored when loaded.


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$Id$

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