czx81 - A CURSES based ZX81 emulator
                         Copyright (C) 2020 Ian Cowburn
              ZX81 ROM Copyright (C) 1981 Nine Tiles Networks LTD

LICENSE
-------

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.


KEYBOARD
--------

    All normal characters should produce the equivalent character if it exists
    on the ZX81.  The emulator assumes you can generate the characters A-Z which
    will be mapped to the equivalent ZX81 key when a lower case character is
    entered.  An upper case character will generate the shifted version of the
    character as it appeared on the ZX81 keyboard.

    The cursor keys should act as cursor keys.

    The ESCAPE key will display the runtime menu.

    The following keys have the following effects:

    F1          - Emulate the EDIT key (shift 1)
    F2          - Emulate the AND key (shift 2)
    F3          - Emulate the THEN key (shift 3)
    F4          - Emulate the TO key (shift 4)
    F5          - Emulate the GRAPHICS key (shift 9)
    F6          - Emulate the FUNCTION key (shift new line)
    F7          - Emulate the BREAK key (shift space)
    BACKSPACE   - Emulate the RUBOUT key (shift 0)
    DELETE      - Emulate the RUBOUT key (shift 0)

    When emulating the keyboard the key is held down for a default of one frame.
    This can be altered in the runtime menu.


LOADING AND SAVING
------------------

    czx81 will try and load the filename you give it in a LOAD command.  It
    looks in a configured directory (the current directory if none is
    configured).  The file must be a ZX81 snapshot .P file.  The directory
    that it loads from can be configured.  See the CONFIGURATION FILE section.

    If you SAVE a file it will save it in the current directory, or the 
    configured one if one is configured.  Note that the ability to save must
    be enabled.  See the CONFIGURATION FILE section.


RUNTIME MENU
------------

    When you press ESCAPE the runtime menu is displayed and offers the following
    options:

    F1          - Toggle tracing on and off.  When on tracing will display the
                  disassembly at the PC and the state of the Z80 registers.

    F2          - Alter the number of frames the key is held down following a
                  keypress.  The default of 1 works OK for BASIC.

    F3          - Reset the ZX81.

    F4          - Quit the emulator.


CONFIGURATION FILE
------------------

    On startup czx81 will read configuration from the file $HOME/.czx81rc

    The following directive can be used:

    snappath <directory>        - Specifies the location of .P files for loading
                                  and saving, if enabled.

    allowsave                   - Allow the saving of files.


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