Request for Williams Defender Hardware Specs
David Clear
I spent some time a while back trying to find a Williams Defender
machine in the UK to no avail so I've got another idea...
I've pulled the Defender ROMs from ftp.spies.com. I don't have arcade
hardware, but I would like to play Williams Defender. My idea (and feel
free to shoot this down if you feel that way inclined) is to write a
simulator for a fast PC.
What I need, for starters, is answers to the following:
1. Which CPU does a Williams Defender machine use and how fast
is it clocked.
2. I have 12 game ROM images and one sound ROM image. How do
the game ROMs map to memory addresses?
3. I believe these machines use memory mapped I/O. Does anyone
know the I/O map and how the hardware works.
I hope questions 1 and 2 are easy to answer... but if the CPU is a custom
chip then I guess it's all over already unless someone has the specs.
Question 3 I'd expect to get little response to, but pointers to other
concrete sources would be appreciated if you can't give me what I need
directly.
Are Williams themselves likely to help or is all this stuff still
company confidential (after 10 years). Does anyone know someone who
works/worked for Williams who might be able to provide the information
I need?
This is all pie in the sky at the moment. It's just for fun. If I ever
got it going I would make it available freely but at the moment I'd just
like to see if it's feasible.
All comments (especially constructive ones) appreciated.
Dave.
Scott Lemon
: This probably sounds crazy, but here it goes...
: Dave.
I remember seeing a message thread regarding something in this area a
while ago. From what I read, some guy at Apple has already done exactly
what you want to do :-(
Apparently, most of the early Williams stuff was 6809 based (Defender?,
Stargate, Robotron, Sinistar...any more???). Anyway, he did a 6809
emulator that runs native on the PowerPC, and also emulates some custom
blitter that Williams had. With the ROM images, I guess you could play
any of those games.
I'd be interested iff anyone has any more information...(like where you can
get this program), or any further info on the Williams internals.
Scott Lemon
sle...@triode.apana.org.au
Alex Rosenberg
(Scott Lemon) wrote:
> Apparently, most of the early Williams stuff was 6809 based (Defender?,
> Stargate, Robotron, Sinistar...any more???). Anyway, he did a 6809
> emulator that runs native on the PowerPC, and also emulates some custom
> blitter that Williams had. With the ROM images, I guess you could play
> any of those games.
Joust and Bubbles were variations of that same board design. Later
Williams games also used a 6809, such as Mystic Marathon, Joust II, etc.
> I'd be interested iff anyone has any more information...(like where you can
> get this program), or any further info on the Williams internals.
The author will not be releasing the application to anybody. There are
obvious copyright issues. He just wanted to prove that the Power Macintosh
can run great games, even if it has to emulate them. If you'd like to know
about the Williams hardware, you should buy one of these early games. They
come with fairly easy to read schematics. If you can figure out the memory
map from the schematics or by watching what the code is trying to do, then
you're in business. I'd suggest that you pick a different game to start.
How about one of the following:
Atari Xevious
Centuri Gyruss
Exidy Venture
Midway Spy Hunter
Midway Tron
Midway Satan's Hollow
Midway Xenophobe
Midway Blasted
Midway Bosconian
Nichibutsu Crazy Climber
Stern Bagman
Taito Elevator Action
Williams Moon Patrol
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MitchPB
writes:
I can tell you what I know about Defender.
Eugene Jarvis was the head of the Defender design team at Williams. In
1982 he
was the guest speaker at an IEEE meeting at SMU. I couldn't attend by my
twin
brother did. My brother and I were big Defender fans, assembly language
programmers, and EE majors so we had allot of questions for Mr. Jarvis.
This is what I can remember:
CPU:
1 MHZ 6809 (Stargate used a 2 MHZ 6809)
Graphics:
- straight bit map 4 bits per pixel
- 16 entry 8-bit palette (2-bits blue, 3-bits green, 3-bits red)
- The graphics screen is at the same address as the ROM so the
screen cannot be read from
- Horizontal resolution 256
- Vertical resolution: 192 (I cannot remember for sure; close to 200)
- No special graphics coprocessor the 6809 did it all (wow)
Sound:
- separate microprocessor board (a 6801 or 6803 I can't remember which)
The system was programmed to produce an interrupt at the start of the
vertical
blanking period and mid-screen. During the mid-screen interrupt the
"sprites"
on the upper half of the screen were erased and re-drawn by the CPU.
During
the VBL interrupt the sprites on the lower half of the screen were drawn.
If you look close on a Defender arcade game you will see a "shadow" of one
pixel when two sprites are one on top of the other. This is caused because
a
byte write by the CPU writes 2 pixels at a time (4 bits per pixel). The
screen
can't be read from to do any type of easy masking. A read from the screen
address range would just read in the ROM data. The 6809 only has a 64K
address
space so address space was very precious. Complex bit masking would take
too
much time. Virtually every thing you see on the screen is re-drawn 60
times a
second.
The ground was simply redrawn too; No scrolling hardware.
The sound was done by sending a sound code to the separate sound board. It
would then play that sound. The microprocessor on that board would send
the
sound data to a D/A converter connected to the speaker. No special sound
chip;
No DMA. Great sounds!
Mr. Jarvis started a company, Vid Kids, with other Williams game
designers.
They designed some of the other Williams video games, like Robotron, under
contract with Williams. If you find a Robotron arcade game you will see
the
Vid Kids memo as part of the attract screen. There was some type of a blit
graphics chip added for Robotron and some of the other Williams games of
that
time period.
My brother has a Defender arcade game. I can look inside for any useful
info
if you would like.
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Mitch Bunnell