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Sega Programming FAQ Sixth Edition
Sega Programming FAQ
Sega Programming FAQ September 14, 1994, Sixth Edition
Modified May 23, 1996 (to reflect changes) by cdoty@host.yab.com
(If you have the Seventh Edition please send it to me
cdoty@host.yab.com)
This FAQ (Frequently Asked Questions) is about how to program
the Sega Genesis and Mega Drive Video Games Systems.
This file IS Public Domain, and can be used by all.
You may copy and post this file elsewhere. Share and enjoy.
If you want to add anything, especially game code or
information on the hardware please E-mail me. My E-mail
and real address are below and at the end of this FAQ.
Disclaimer : In no way I am endorsing any products, systems,
etc. What I am doing is providing the information that I
have found throughout internet and other network systems and
reporting them here, with out reverse engineering. All
information is reported as is- I will not accept any
responsibility if you fry your system trying something out.
All copyrights are owned by their respective owners, no
infringements intended.
Henry Rieke
US Mail:
Henry Rieke
Attn: Sega FAQ
161 Poplar Dr
Morgantown, Wv 26505-2340
Modified by:
Charles Doty
0.1 Changes, Updates and Coming Soon
1) Graphic, Video, and processor maps have been added. Major stuff here.
In fact, enough to being programming your own games.
2) Coding for the four player tap from Electonic Arts has been added.
Does anyone have the code for the multi-tap from Sega, and how it works?
3) I am now beginning to work on a topic header on languages that
you can program in for the Sega and Sega CD ROM. If you have any
direct information (compiler, how to compile, etc) let me know so
I can include it.
4) I've (Charles Doty) written a Sega Assembler, Disassembler. Included with
this is some source code. Currently the source only puts a text message
to the screen. I've got a working sprite but haven't released the code yet.
It's available at http://www.yab.com/~cdoty/Console.html
1.0 Questions
Q) What are the differences between Mega Drive and Genesis?
What are the differences between Mega CD and Sega CD?
A) Physically, on the outside, the only difference is the
plastic case, the cartridge shape is slightly different on
the American version, smaller in size. On the inside there
are four jumpers labeled J1 though J4. J1 and J2 is the
language switch, between English and Japanese, J3 and J4
select the output between PAL and NTSC. You can build a
switch that can allow you to select between these options.
The diagram is included in this document (Chapter 5.0,
called "Language Switch"). The reason for the language
switch is to keep people from getting the game before it
is officially released elsewhere in the world. The newer
Sega Machines do not have the jumpers, and hence you can
not build a switch (as of yet).
The difference between Mega CD and Sega CD are internal.
In side the machine there is a ROM BIOS chip which is changed
for different markets. Sega has a version of the BIOS which
will play any system's games, but this is for Game developing
and testing. There is a device called Pro-CDX which will allow
you to by-pass the lockout and play any country's games.
Q) Where to find files on the Sega Genesis/Mega Drive
hardware?
A) You can find the files on the Sega hardware from one of
the following FTP sites. A brief section describing memory
and cartridge ROMs are included in this FAQ. The author
Rick McTeague, is from Louisville and the most current copy
can be found there first.
FTP ftp.spd.louisville.edu
/pub/sega/hardware.txt
FTP sunsite.unc.edu
/pub/micro/games/sega/faqs/incoming\hardware.txt
It's in there. I'm not sure of the exact location.
Q) What does it take to program the Genesis?
A) Development kits can be bought from many companies, a list
is included in the section called "Companies". These kits
require an IBM or Amiga computer to compile the code,
which is usually assembly, but can be in C as long as it
can be compiled into 68000 binary. SEGA's own kit is extremely
expensive and they are rumored to have slow response time
to answer questions. The price of the kits cost from $1000
to $4000.
Q) Is IBM or Amiga the only two platforms for game
development?
A) No. The Apple Macintosh does have a system, which does allow
you to compile games, but it is a do-it yourself job (See below
for the whole scope). There also is a system for the Apple IIgs,
called Sluggo from Parsons Engineering. As for the Mac, if you
know, please pass it on. It is rumored that Electronic Arts uses
a priority system on the Macintosh for porting the games.
-- This information comes from Landon Dyer ,
-- You can generate 68K code for the Sega "trivially" with the
C compiler and assembler in the Macintosh programmer's workshop
(MPW). You'll need to hack up some transfer utilities, but this
is not really hard. You can wire-wrap a ROMulator, or buy one;
there are a bunch on the market that should work just fine.
I had a ROMulator and a debugger up and running in about a
week, working evenings. (Ed note: ROMular information can be found
at the FTP sites)
Q) How do I program the SEGA CD Rom?
A) I am beginning to understand how to program this device,
but more information is needed, so if you have any, please
pass it along to me so I can include it in the next update.
Look under Hardware 2.1, Sega CD for more information about
the unit.
Q) What is Saturn, and how do I program that?
A) Saturn is Sega's next generation game machine, which
is based on Sega's S-1 /S-2 arcade Machine's motherboard.
Rumor has it that it will allow programming in C as
well as Assembly, and porting of arcade games that are
based on the S-1 and S-2 boards will take only a week.
There is good news and bad news as well.
Good news, Microsoft will be writing the OS.
Bad new, Microsoft will be writing the OS.
Q) What else is there on Internet?
A) Http://www.yab.com/~cdoty/Console.html contains a Sega assembler,
disassembler and some simple source code.
There is also Rec.Games.Video.Sega where you can ask your questions.
There are also files on how to use the old SEGA 3D glasses
with your IBM compatible computer which can be found all
over the place (including the above FTP sites).
2.0 Hardware : This is the inner workings of the Sega system
ROM and Memory. For a better understanding Sega Hardware I
suggest reading Hardware.txt. An up-to-date version of this
file can be gotten by anonymous ftp from Ftp.spd.louisville.edu,
in the file "Pub/sega/Hardware.txt".
Genesis - this information comes from Rick McTeague.
Sega Genesis Hardware Internals - Revised: 04/07/1993
Please send corrections or comments to:
Rick McTeague
Sysrick@starbase.spd.louisville.edu
Disclaimers:
The following information was extracted without the use of
official information from Sega Enterprises, Ltd. I therefore
offer no warranty on the correctness of this information.
Use it at your own risk.
This information was gathered as a personal project, and is
not the responsibility of my employer.
Different versions of the Genesis exist, so I won't suggest
that any of this information is right for anybody's Genesis
but my own.
Sega, Genesis, Sonic the Hedgehog, and Ecco the Dolphin are
trademarks of Sega Enterprises, Ltd. Other trademarks are the
property of their respective companies.
The Cartridge ROM
-----------------
As others on the net have observed, a standard Genesis
cartridge is nothing more than a small printed circuit board
with a ROM on it. There are some cartridges which have
battery-backed RAM for saving high scores, configurations,
etc., but I haven't seen these, so I don't know about them.
If you know of a particular cartridge that has RAM, let me
know so I can go rent one and take it apart (shhhh!) to see
what's in it.
A cartridge contains a word-wide (16 bit) ROM with up to 2
Meg words (4 Mbytes). This is based on the signal !C_CE, which
is used as the cartridge ROM's chip enable on the cartridges
I've looked at, and which is active at addresses $000000-$3fffff.
It may be possible to have more than 4 Mbyte cartridges; if
so, either they ignore the !C_CE line and do their own
address decoding, or there's a register somewhere in the
Genesis which changes the default address decoding scheme for
!_CE.
Note that cartridges are advertised as being "8 Meg"; as far
as I know, is 8 Meg _bits_, not bytes. 1 Mbyte is still
pretty impressive for a game machine.
SONIC uses a 40-pin 256Kx16 (512Kx8) ROM in word mode.
Ecco the Dolphin uses a 42-pin 512Kx16 (1024Kx8) ROM in word
mode. This one confused me because I'd never seen a 42-pin
DIP before, so I thought it was 40 pins. No wonder the
signals didn't look right...
Putting together a little bit of information from a Sharp
data sheet for a 512 Kword ROM with a bit of conjecture based
on the Sonic and Ecco cartridges, this is what I can come up
with for pinouts:
Sonic Ecco
(256 Kword) (512 Kword)
----u----
----u---- A18 1=| |=42 VCC?
A17 1=| |=40 A 8 A17 2=| |=41 A 8
A 7 2=| |=39 A 9 A 7 3=| |=40 A 9
A 6 3=| |=38 A10 A 6 4=| |=39 A10
A 5 4=| |=37 A11 A 5 5=| |=38 A11
A 4 5=| |=36 A12 A 4 6=| |=37 A12
A 3 6=| |=35 A13 A 3 7=| |=36 A13
A 2 7=| |=34 A14 A 2 8=| |=35 A14
A 1 8=| |=33 A15 A 1 9=| |=34 A15
A 0 9=| |=32 A16 A 0 10=| |=33 A16
!CE 10=| |=31 !BYTE !CE 11=| |=32 !BYTE
GND 11=| |=30 GND GND 12=| |=31 GND
!OE 12=| |=29 D15 !OE 13=| |=30 D15
D 0 13=| |=28 D 7 D 0 14=| |=29 D 7
D 8 14=| |=27 D14 D 8 15=| |=28 D14
D 1 15=| |=26 D 6 D 1 16=| |=27 D 6
D 9 16=| |=25 D13 D 9 17=| |=26 D13
D 2 17=| |=24 D 5 D 2 18=| |=25 D 5
D10 18=| |=23 D12 D10 19=| |=24 D12
D 3 19=| |=22 D 4 D 3 20=| |=23 D 4
D11 20=| |=21 VCC D11 21=| |=22 VCC
--------- ---------
Note that the address line numbering is different than that
of the 68000; line A0 of the ROM is really connected to the
68000's A1. This is because of the way the 68000 handles
even/odd byte addressing using !UDS and !LDS.
The !BYTE line is held high. This puts the ROM chip into
"word" mode, where data is accessed 16 bits at a time.
The convenient correspondence between ROM and 68000 data and
address lines (ROM D0 = 68K D0, ROM D1 = 68K D1, etc..., and
ROM A0 = 68K A1, ROM A1 = 68K A2, etc...) may not exist in
all cartridge designs. This is sometimes difficult to
visualize, but keep in mind that the ROM doesn't care whether
its D0 is really D0, or if its A3 is really A3, etc. As long
as each data line is used as the same D## line for both
programming and reading, and each address line is used as the
same A## for both programming and reading, the ROM will
function properly and the 68000 will see the right
instructions. Think about it...
Why bring this up? If you remove the ROM from the cartridge
PCB and try to read it with a EPROM programmer, there may be
situations where you won't see valid 68000 instructions, or
things won't be in the right place... Assuming your
programmer isn't messed up, this would be because the address
and data lines on the ROM aren't assigned the way you'd
expect.
Why would someone make a cartridge like this? To make your
life difficult, if you're wanting to hack their ROMs, or to
make their life easy, by making the cartridge PCB easier to
design.
The easiest way to avoid this potential problem is to build
an adapter from your programmer's EPROM socket to an edge
card connector into which you plug the cartridge. This is a
bit safer, too, so you don't have to remove the ROM from the
cartridge (or even open it up).
The Memory Map
--------------
$000000 $3fffff Cartridge ROM, when enabled by cartridge
control register and !CART_IN.
$000000 $0007ff Internal OS ROM, when enabled by cartridge
control register and !CART_IN.
$ff0000 $ffffff 64Kbytes scratchpad RAM
Partially decoded; RAM actually appears repeated between
$e00000 through $ffffff.
$a14101 cartridge control register
bit 0 = 0: cartridge disabled, OS ROM enabled
bit 0 = 1: cartridge enabled, OS ROM disabled
$a00000 $a????? Unknown. Audio? Controller I/O?
$c00000 $c????? Video display controller registers
The OS puts the top of its stack at $ffff00, and defines a
"user stack pointer" at $000000 (building down through the
top of RAM memory).
The Z80 processor is used for sound and has 8Kbytes of RAM.
I don't know anything about how the Z80 does its work, as I
haven't looked.
Acknowledgements
----------------
Thanks to:
dt93tn@pt.hk-r.se (Tore Nestenius) for info on older Genesis
systems.
lewism@rpi.edu (Michael Lewis) for info on the Sony CXA1145
and Samsung KM6264 chips.
crs@crs-sys.uucp (Chris Gregors) for posting a version of the
Genesis cartridge port pinouts.
merlyn@digibd.com (Brian Westley) for Game Genie information
and decoder program.
Brief technical description of the Genesis:
---
The genesis graphics hardware consists of 2 scrollable planes.
Each plane is made up of tiles. Each tile is an 8x8 pixel square
with 4 bits per pixel. Each pixel can thus have 16 colors. Each
tile can use 1 of 4 color tables, so on screen you can get 64
colors at once, but only 16 in any specific tile. Tiles require
32 bytes. There is 64K of graphics memory. This would allow
for 2048 unique tiles if memory were used for nothing else.
Each plane can be scrolled independently in various ways.
Planes consist of tables of words, where each word describes a
tile. The word contains 11 bits for describing which tile, 2 bits
for flip x and flip y, 2 bits for the selection of the color table,
and 1 bit for a depth selector. Sprites are composed of tiles also.
A sprite can be up to 4 tiles wide by four tiles high. Since each
tile is 8x8, this means sprites can be anywhere from 8x8 pixels to
32x32 pixels. There can be 80 sprites on screen at one time. On a
scan line you can have 10 32 pixel wide sprites or 20 16 pixel wide
sprites. Each sprite can only have 16 colors but they are out of the
4 different color tables. Color 0=transparent.
Colors are 3 bits for each gun, so 512 colors are possible.
There is a memory copier that is in hardware. This does fast copies from
the 68000 ram into the graphics ram.
The 68000 runs at about 8 mhz. It has 64K of memory devoted to it. The
ROM cartridge appears at 0.
The Z80 has 8K of ram. The 68000 can download programs to the z80 and
let them go. The z80 can access the graphics chips or the sound synth
chips but usually those things are controlled by the 68000.
The sound chips consist of a Yamaha synthesis chip and a TI programmable
sound generator. The PSG has 3 square wave tones and 1 white noise tone.
Each tone/noise channel can have its own frequency and volume.
The Yamaha chips are based on FM synthesis. There are 6 voices with 4
operators each. The chips are similiar to those used in the Yamaha
DX27 and DX100 synthesizers. By setting up registers a rich variety of
sounds can be created.
2.1 Sega CD Rom. The following information came from
Leyland@island.COM (Robert Leyland), who was a programmer for the
most excellent Sega CD Rom game - Flying Aces. (Plug!Plug!
Plug!Plug!Plug!Plug!)
-- The Sega CD is ISO 9660 format, with proprietary start-up code
that must be licensed from SEGA in order to work. For programming
you use two PC's, one connected to a debugging system and the other
emulated an CD-ROM drive.
The trickiest part of programming the Sega CD/Genesis combo is
keeping the two CPU's synchronized. For some reason the single
hardest thing to do with any computer is get it to talk reliably
with another computer.
2.2 Joystick - 3 button version - Could some please post a 6
button version?
By: nhowland@matt.ksu.ksu.edu (Neal Howland) for information
on the Joystick port.
First some background info: The chip inside the controller
is a 74HC157. This is a high-speed cmos quad 2-line to
1-line multiplexer. Basically how this works is there are two
inputs ( A and B ) for every output ( Y ). There are four
groups like this. There is one select signal for the whole
chip. When the select signal is low, the output ( Y ) is the
same as input A. When the select signal is high, the output
Y is the same as input B. The pinout for the chip is as
follows:
Pin 1 - SelectPin 16 - Vcc (+5V)
Pin 2 - 1APin 15 - G (? must be low)
Pin 3 - 1BPin 14 - 4A
Pin 4 - 1YPin 13 - 4B
Pin 5 - 2APin 12 - 4Y
Pin 6 - 2BPin 11 - 3A
Pin 7 - 2YPin 10 - 3B
Pin 8 - GndPin 9 - 3Y
All the controls are done with switches. Up is a switch,
Down is a switch, etc. Now, I will be referring to the output
of these switches later on. What I mean is that the output is
usually high, that is when the switch isn't pressed.
When the button is pushed, the output goes low. This is
accomplished by connecting the output to +5V through a 10k
resistor. The button is then attached between the output and
ground. It looks like this:
+5V ---- /\/\/ -----+--------- Output
10k |
|
/ |
Ground ---- / -------+
button
(normally open)
For all of those who could actually decipher the above
schematic, congratulations!
I will now run down what lines from the plug are connected to
what. The line numbers are determined as follows, looking
straight at the plug on the front of the Genesis the numbers
are:
1 2 3 4 5
6 7 8 9
(For those of you who buy a joystick cable from radio shack
the pin #'s to wire colors are as follows: 1-white 2-blue
3-green 4-brown 5-yellow 6-orange 7-red 8-black 9-gray )
anyway, line connections:
Line 1 - Up output These are the only two direct
Line 2 - Down output connections
Line 3 - Pin 4 of the chip output 1Y
Line 4 - Pin 7 of the chip output 2Y
Line 5 - This line carries in +5V. It is connected to the
+5V bus line.
Line 6 - Pin 9 of the chip output 3Y
line 7 - Pin 1 of the chip this carries in a select signal
from the Genesis. This is a signal which varies
rapidly and controls which input goes through the
output.
Line 8 - Ground This is connected to the Ground bus line.
Line 9 - Pin 12 of the chip output 4Y
Now for the chips pin connections:
Pin 1 - Line 7 (select)
Pin 2 - Ground (1A) Don't ask me why they do this. Maybe
Pin 3 - Left (1B) future expansion
Pin 4 - Line 3 (1Y)
Pin 5 - Ground (2A) Again, possibly future expansion
Pin 6 - Right (2B)
Pin 7 - Line 4 (2Y)
Pin 8 - Ground (GND)
Pin 9 - Line 6 (3Y)
Pin 10 - Button B (3B)
Pin 11 - Button A (3A)
Pin 12 - Line 9 (4Y)
Pin 13 - Button C (4B)
Pin 14 - Start (4A)
Pin 15 - Ground (G) This must be connected to ground
Pin 16 - +5V (Vcc) Power source for the chip
Anyway that's all the info needed to build your own joystick.
Now as an added bonus, additional information!
A simple source for a joystick cable is the Radio Shack
joystick extension cable. It is around $5 and is 10 ft. long.
Just snip off the connector that won't plug into the Genesis,
strip the wires back, and use the color pinout list I gave
above.
I went to my local arcade game repair company today and
purchased the supplies I needed. They were much cheaper than
I expected. Things you would need to buy from them would be:
an 8-way joystick this ran me $15
3 buttons $2.50 apiece
I only bought three buttons because I am going to use a Radio
Shack push button switch for my start button. You can purchase
4 arcade game buttons if you wish.
Interesting ideas for extras on the joystick:
1. Autofire can be achieved with a simple 555 timer circuit.
For anyone wanting a challenge it should be possible to
build a digital autofire using a divide-by-n counter with the
select signal as clock input.
2. Slow down mode is just autofire for the start button.
3.0 Companies - these companies produce the hardware that is
required to write games for the Genesis. The original
document came from: Scott Golby
Hi Everyone,
Here is the current list of info I have about the Sega.
I have had about 10 replies so far asking to pass my
info on. If people want I will pass their EMail address on
to everyone else so we can work as a group. Drop me a line
if you want to be added to the 'group' list.
***** < ---- Five astrict like this means info from
different people
Sega Genesis Developer Resources
Dan Chang April 18, 1993
Sega of America Inc
Consumer Products Division
125 Shoreway Road
San Carlos, California, 94070
Tel : (415) 802-4400
Fax : (415) 802-4458
Stuart Kosoy is the person to contact at Sega of America
at (415)802-4407.
Products : Detailed SEGA Genesis technical information. GEMS
SEGA music development package.
Solution : Music and Sound effects package for the Sega. SOA
can provide detailed information on programming the Genesis;
however they will want to know more about your company first.
Western Technologies, Inc.
12057 Jefferson Blvd
Culver City, California, 90230
Tel : (310) 821-7880
Fax : (310) 306-1739
Products : SegaDev Card. PC-Hosted Genesis development
hardware, which includes SEGADEV.EXE, a Windows-hosted
source-level debugger, and SEGALOAD.EXE, a PC_hosted 68000
object code downloader.
Solutions : SEGA Genesis Hardware, WT recommends Sierra
Systems 68000 Assembler.
Sierra Systems
6728 Evergreen Ave
Oakland California 94611
Tel : (510) 339-8200 or (800) 776 4888
Fax : (510) 339 3844
Products : PC-hosted Sierra C cross-compiler, which included
68000 C compiler, assembler, linker.
Contact person at Sierra Systems is Larry Rosenthal
E-Mail Sierra@netcom.com
Motorola, Literature Dist
This entry basically has a list of 68000 reference and
programming books.
Echidna
1101 W Stevens Ave, Suite 232
Santa Ana California 92707
Tel : (714) 545-2662
Fax : (714) 545-3705
Products : tUME - the Universal Map Editor. PC-Hosted tool to
edit tile-maps.
Solutions : Saves time in designing game maps and placing
level information. Downloads maps to Western Techs SegaDev
card.
Cross Products Limited
23 The Calls
Leeds LS2 7EH, England
Tel 0532 429814
Fax 0532 426163 (dial 011 44 532 426163 from USA)
Product : SNASM68K : PC-Hosted SEGA Genesis development
system, which includes a 68000 assembler, linker, debugger.
Parsons Engineering
Imhurst Ave
Covina California 91724
Tel (818) 966 5538
Products : PC/Apple IIgs hosted Sluggo Genesis development
hardware.
Advantech
1333 E.9400 South, Suite 160
Sandy Utah, 84092
Tel : (801) 572-5410
Fax : (810) 572-5674
Products : blank SEGA Genesis cartridge PC boards, blank
EPROMS.
*****
Genesis Development System Frequently Asked Questions
Q:What is the Genesis Development System?
A:The GDS is a cross development system that lets you develop games and other
software to run on the Sega Genesis. The system consists of a 4 inch by 8
inch printed circuit board that plugs in the cartridge slot of the Genesis,
and has a cable going to the parallel port of the host computer. A complete
software set is included consisting of an integrated editor/assembler, a
stand alone assembler, a symbolic debugger, a music and sound effect editor,
a utility to break standard 16 color IFF images into tiles to be downloaded
to the Sega, a utility to capture screen graphics on the Genesis, a
utility to send an LBM image to the Genesis for preview, a linker for
joining multiple object modules, and several example files.
Q:Does it come with any source files?
A:You get source to the music editor, source to a Z80 program to run on the
genesis to interpret the music files, source to a demo program that plays
music and has sprites bouncing around behind the Sega logo, source to the
download utilities. Complete source is provided on communicating between
the host machine and the Genesis.
Q:How much memory does it have on the board?
A:It comes with 2.25 or 4.25 megabytes of memory. Older versions had 1.25
megabytes. 256K is reserved for use by the debugger for variable
storage and symbols.
Q:Can you program CD games with it?
A:It is not specifically designed for a CD. You could program as if you're
creating a cartridge then modify the code later to make it work on the
CD. I provide no information on the Genesis CDROM drive. I don't own one
myself. The Genesis CDROM market is perhaps 10% of the cartridge market.
Q:Does it include technical specifications for the Genesis?
A:Yes, it comes with descriptions of the memory map, graphics registers, the
Z80's functions, reading the joysticks, sprites, scrolling, tiles, the
DMA copier, the audio chips-in short everything required to program the
genesis. Also provided are several working demos with source.
Q:Is this proprietary information stolen from Sega?
A:No, the information on the Genesis came from reverse engineering it,
completely independent of Sega. There are no copyright violations in the
purchase or sale of this development system, nor is there anything illegal
about any use of it.
Q:How does it work?
A:The board has ROMs on it which contain the monitor and debugger that runs
on the Genesis. When the Genesis is reset, the ROMs take over and wait for
commands to come from the host machine-commands like download bytes, send
bytes back, set up registers, define a symbol, or enter the interactive
debugger. When in the interactive debugger the host machine acts as a
terminal, and characters are sent over the cable. Full 68000 debugging
is possible, including disassembly, single step, register view and modify,
breakpoints, expression evaluation, memory view, modify, search and copy,
symbol definition, memory compare. There is also a z80 disassembler built
in.
Q:What about the assembler?
A:The assembler is a full macro 68000 assembler, and includes the full 8080
and parts of the Z80 instruction set. It generates symbol table information
that can be downloaded to the Genesis to allow for symbolic debugging.
On a 66 Mhz DX2 the assembler is about 550,000 lines/minute. There is also
a linker which combines multiple object files.
Q:Can I program in C?
A:There is no C compiler included in the package. In the future there
may be.
Q:How do I make artwork? Is there a sprite editor?
A:Originally I planned on including a simple graphic editor, but I found that
no one used it-instead they used Dpaint. The best way is to use dpaint to
create graphics in lo-res 16 color mode, then to use the utility I provide
to convert them to raw data to be sent to the Sega. Animation can be done
within Dpaint. Unfortunately there is no editor for manipulating giant
figures made out of sprites, but in principle it would be possible to do. So
probably you will use dpaint or some other painting program to create the
artwork.
A:Can you backup existing cartridges like the game backup systems?
Q:The system is intended for game development. However if you were able
to obtain ROM images, they can be downloaded just like original code.
When running a ROM under the system, you can tinker with memory, modify
gameplay, add lives, etc. You can do all the normal debugging functions,
like single step, breakpoints, etc, to see how the program is working.
In the future (Mid March, 1994) a reader will be available for $100 which
will let you read out the contents of your cartridges.
Q:How fast are downloads?
A:The current board has transfer rates of up to 105K bytes per second. Older
versions of the board had a 49K bytes per second transfer rate.
Q:What host machines is this available on?
A:Currently the complete system is available on the IBM PC. There is also
an Amiga version but it has fewer features than the PC version.
Q:Why should I buy your system and not go through Sega?
A:My system is better and cheaper than those provided by Sega. I sell to
anyone. Sega sells only to large companies. I require no non-disclosure
statements to be signed. Sega requires you to sign extensive non-disclosure
statements, and you essentially have to be subservient to them forever.
If you buy my system you immediately have the ability to create software
for the Genesis. If you create a game, you can then sell it outrifht or
attempt to publish it yourself. You wouldn't have to pay Sega any of their
rediculous royalties on each unit, regardless of how well your program
sells.
Q:How long has this system been available?
A:It first became available in April 1991. The 2 and 4 megabyte versions
first became available in February, 1994.
Q:How many have already been sold?
A:I've sold around 30 units so far.
Q:How much does it cost?
A:For the 4 megabyte version the cost is $1600. For the 2 megabyte version
the cost is $1500. For the duration of March, 1994 there is a special
introductory price of $1000 for the 2 megabyte version and $1100 for the
4 megabyte version. After March, 1994 the price will be raised by $500.
Q:Will it be ported to other platforms?
A:There are no plans to port the software to any other platforms.
Q:What about technical support? How about software upgrades?
A:You can send me email and I will answer questions and help solve your
problems. If I'm home you can call me. Concerning software support: I want
you to be happy with this. If you want some program written, and it seems
like a good idea, chances are I'll do it for free and include it with the
system. Currently if the software seems sparse it's because no one has
complained so I guess I include enough. There's no point in writing
software if it isn't going to be used. In any case software upgrades are
free unless it's some major upgrade like including a C compiler-I don't
believe in selling something for hundreds of dollars then nickel and diming
you on upgrades. EPROM upgrades are free if you send back your originals.
Q:Do we need to pay you any royalty on games developed with the system?
A:No. Once you bought the system you can do anything you want with it-except
copy it and sell it yourself...
Q:How can I contact you?
A:Send me mail, email or call.
818-584-0357
INTERNET: dash@netcom.com
David Ashley
395 Sierra Madre Villa
Pasadena, CA 91107
USA
4.0 Code samples. The following code was graciously given to
me by David Ashley, inventor of the GDS. We all owe him a big
Thanks!
Here's sample code for reading the joystick:
------------
jsinit must be called to set up the joystick, otherwise
reading back will have errors. This need only be called
once.
jsinit: moveq #$40,d0
move.b d0,$a10009
move.b d0,$a1000b
move.b d0,$a1000d
rts
The following two routines can be used for reading from the
joystick port
