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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.
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.
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 :-)
-------------------------------------------------------------------------------
$Id$
vim:expandtab:spell
|
