W Williams Arcade Games Info

Welcome to Riddle's Roost

This portion of my web site is devoted to the classic Williams games of the early '80s- Defender, Stargate, Robotron, Joust, Bubbles and Sinistar. I have a Joust machine that has been modified to play all of these games, and much of the information that I have gathered over the last couple of years has been compiled here.

Please leave me feedback if you find any errors or know of any omissions: seanriddle {at} airosurf {dot} com

Please read my FAQ before emailing me a question- it's probably in here!

This page up since 6/15/95.

Note: graphics and sounds from the games are copyrighted by Williams Electronics. The programs and schematics are public domain, although I would like to be notified if you will use them for commercial purposes.


o News

o Game Screen Dumps

o Game RAM Dumps

o Williams-related software (disassembler, checksum, etc.)

o Williams Conversion Articles

o Pictures of my Williams Multi-Game machine

o Sounds from Williams games

o Hardware/Software Info

o Other Links

oMy Midway Page

My Cinematronics Page


Splat! Patch 2

I was asked about the Splat! patch, so I did some more research

Robotron Disassembly

Scott Tunstall has been disassembling the Robotron ROMs. Keep checking for updates.

using an SC1 in place of an SC2

Special Chip 2s are hard to find, so here's an adapter to use an SC1 instead

a peek inside the 55516 CVSD IC

Die shot of the 55516 CVSD voice encoder/decoder used for Sinistar speech.

in-depth Special Chip info

More info than you want to know about the blitter chips, including a decap

MAME as a hacking tool

MAME is an excellent tool for hacking video games.

Logic Timing

I connected a Logic16 analyzer to various timing signals on my Joust board to illustrate the relationships between different clocks.

Williams Emulation Test Suite

I began writing a test suite to help out everyone writing Williams emulators or recreating Williams games in FPGAs.

graphics ripper

I rewrote my graphics ripper in Visual C++. Here are some pics and technical info, along with the program and source.

removing the lines from the top of the screen

Here's an explanation of those lines you see at the top of your game, and how to remove them.

notes on patching ROMs

Here are some tips on patching ROM images

6800 disassembler

I wanted to look at the Sinistar sound code, so I modified 6809dasm to disassemble 6800 code. I've also posted a preliminary .dat file for Sinistar. 6800dasm

new multigame hardware

Again, it's been a long time, but I've built new multigame hardware. Take a look here for details.

Up what? What date? What what?

Wow, it's been a long time, but there are a few new things. RoboMax - a patch for Robotron to remove the 5-high scores limit.

New executable programs recompiled to work under Windows.

I got the Playstation games Williams Arcade's Greatest Hits, Atari Anniversary Edition Redux and Namco Museum, so I built a control panel.

shockwave arcade games

shockwave.com recently added ten classic Midway arcade games that include Defender, Joust, Spy Hunter, Rampage, Robotron 2084, Defender II, Sinistar, Bubbles, Tapper and Satan's Hollow. Digital Eclipse converted these from their CDs.


I've written a FAQ to help answer some of the questions that I'm asked over and over again. Please read it before asking me a question. Thanks!

Blitter Test Files

I've uploaded a set of files that demonstrate the use of the Williams special chips. These files are named BLITTEST.*. I've got a program, its 6809DASM .dat file, the RAM dump and a .gif. Here they are.

Lotto Fun

Thanks to Lawnmower Man and Mike Balfour, I got Lotto Fun- a "ping pong balls in a blower" type lottery game. It is copyright 1987 H.A.R. Management Inc. If anyone knows anything about them, please let me know. It is an interesting game- nice fonts, good colors, color cycling, screen fades. It uses the CMOS RAM for adjustments and bookkeeping totals. It works on a Bubbles setup, but only uses the 1 player start button. It will work on Robotron, using just one of the joysticks and the 2 player start button. It won't work on Sinistar, Defender or Stargate, but would work on Joust, although you can't move left or right. You choose 3, 4, or 6 numbers to match, then you win from 5-5000 tickets or tokens if you match. Of course, I don't have a ticket dispenser, so I get the message 'CALL OPERATOR' when I win, and I have to clear it with the advance button. I was also able to get it to run in MAME as Bubbles and Robotron, although the colors are wrong, it doesn't color cycle, and it hangs after the reset screen. You can get it to go past by holding down the '5' key, but you can just see the demo, not play. I've got screen shots and a 6809DASM .dat file.

New look

Hey, I tidied this place up a bit and fixed some of the out-of-date links. Sorry it took so long.... I also fixed my page counter again. Please let me know if something doesn't look or work right.

Cinematronics MultiGame started

Look for a new page soon.... I got a Star Castle, and I've begun work on a multigame. I'm attempting to use a single 27C040 which would give me room for up to 16 32K games. Of course, I've got to work on the control panel, and the sound boards are going to be a big problem. I also have a bad high voltage unit which is slowing me down a lot. If you have a Keltron HV unit for sale, please leave me email. I'd also like to borrow some sound boards to digitize the sounds, and I'd love to get a copy of Tail Gunner's schematics. Thanks!

SRAM mod

Tired of changing batteries every 6 months, I replaced my SRAM with a Dallas chip that has a self-contained battery. It is a straight swap for the 6264 that I was using. All I did was yank the batteries from the CPU board.

Defender Hack II

I added 3 more chips to my Joust machine to make it more similar to Defender's hardware so that I can run Defender without any ROM hacks. Well, I actually have to clear 3 bits(!) so that the sound board will work. And there is a slight graphics glitch during the rug RAM test until the demo starts, but then everything is perfect.

Williams Arcade Classics Win95

I just got my copy of WAC Win95. In addition to the new versions of the games, it includes the DOS versions. The new versions use seperate uncompressed ROM images, making hacking easier. The sound files are .wavs, so you can play around with those as well. Look for some hidden goodies! I found something that I'd been wondering about for a while. Also look for me under 'beta testers'!

Counter Overflow?

My hit counter on this page had somehow reset. I'm not sure exactly how, but I counted the entries in my hit database, and updated my counter.

Z80 disassembler

I've posted the source code for my Z80 disassembler on my Midway page. This program is very similar to my 6809 disassembler, with support for distributable data files. Please send me any you create!

PC Executable Programs

I've finally compiled my software for the PC. I've posted the .exe files along with the source code.

Splat info!

Splat is an (almost) unreleased Williams game from 1982. It runs on nearly the same platform as the other Williams games of that era, except that it expects Special Chip 2s instead of SC1s on the ROM board. I've posted a bunch of pics from the game, as well as a software patch to use SC1s. There is a circuit in the hardware section that lets you use SC1s without the software patch. Splat is sort of a cross between Robotron and Food Fight. You chunk pies, apples, fish, bananas and other food items at your foes (and the other player, in a 2 player game). If you are hit, your head flies off and you must recapture it before you can throw any more food. If you are hit without your head, you lose a life. Splat is wave-based, like the other Williams games, but is unique in that the waves are timed. You can grab food as it falls from the top of the screen, and if you time it right, you can grab food thrown at you. There are also keys that you can throw, or use to go through one of the four doors (2 on each side of the screen) that take you to the other side.

Pterodactyl-bug Joust Patch

I've posted a patchfile to modify the JOUST.EXE game of Williams Arcade Classics from the green ROM image to the yellow image. This ROM revision has the well-known 'pterodactyl bug'. You can find the patchfile in the software section.

New Utility Programs Added

I've made available several utility programs:

uncomp.c - source code to uncompress the Williams Arcade Classics ROM images

splitter.c - source code to a file splitter - convenient for splitting ROM images

joiner.c - source code to a file joiner

You can find them in the software section.

Bug-fixed Robotron Patch

It is fairly easy to patch the blue-labelled Robotron ROM image to remove the 'shot-in-the-corner' crash. I've posted a patchfile and a program that can make patches using a patchfile. You can find them in the software section.

Digital Arcade's Williams Arcade Classics

Well, the games are out now for DOS. You get Defender, Defender II, Roboton, Joust, Bubbles and Sinistar for about $35. The games use a 'Williams Emulator' to run the actual arcade game code, so they are very authentic.

You can check out info here.

Software ROM Switcher Built

I used the parallel port (see below) to control the 3 game select address bits on my Multi-Game EPROM. I wrote 6809 code that I burned into game position 0 of the EPROM that puts up a picture, displays graphics from one of the games, and plays a sound. Then it waits for the player to hit the 1 or 2 player start button; when the 1 player button is hit, the graphics are updated to the next game and a different sound is played. When the 2 player button is hit, the correct ROM image is selected, and the reset vector jumped to. This starts the game at the normal 'rug' RAM test. When the reset button is hit, the parallel port latches are cleared, and my ROM switch code is run again. I put up a picture in the Multi-Game pictures section, and the code and a .DAT file for my 6809 disassembler are both in the Software section. NOTE- to accomodate the Robotron bug fix, I had to change the hardware address of my port. The code and schematics have been updated. I added the ability to load a game's CMOS RAM, so you can restore high scores that have been cleared. I also added a function to trash CMOS RAM so you can get the machine to reset EVERYTHING to defaults.

8-bit parallel Port Built

I added two 4-bit latches and a simple address decoder to my Multi-Game machine to create an 8-bit parallel port. I wrote 6809 code to dump the contents of RAM to my Amiga using a simple handshaking protocol. I then modified my graphics scanner to display the screen dumps. I've added a new section of pictures, and the port is described in the conversion section.

Speech PCB artwork available

Frederic Vecoven has taken the Speech board schematics and has laid out a printed circuit board. Here's the link.

Special Chip hack finished

I have made a small circuit that allows Special Chip 2 ICs to be used in games that require the Special Chip 1, and vice versa. See the conversion section.

Sinistar Speech Board Built

Paul Astrachan located some 55564 ICs that are pin-compatible with the 55516s used on the Williams speech board. I built the speech board, using a 27128 to hold the ROM image from the 4 EPROMs. I used a 7408 to decode the 4 EPROM select signals into *CE, *OE, A12 and A13. The hard part was the analog side: too many caps and resistors! But it works, and I now hear 'I hunger!', 'Run Coward!' and all the rest. You can find a picture of my speech board in the pictures section and the schematic of the EPROM addressing circuit in the conversion section. There's also a link to Harris' online 55564 data sheet.

Defender added to my Multi-Game machine

With a combination of hardware and software hacks, I have finally gotten Defender up and running on my Multi-Game machine. The hardware implements the bank-switching circuit that Defender used to access 7 of its ROM chips. The software patches change the references to the ROM and WidgetPIAs, the Watchdog and the CMOS RAM to the addresses used on the newer games.

BTW- the .gif file of the hack had a small error- the gate shown going to the 74157 pin 2 is supposed to be an OR gate, not a NOR gate. The schematic has been fixed. Thanks to Paul Astrachan for noticing.

Sinistar added to my Multi-Game machine

I have gotten Sinistar up and running on my Multi-Game machine, joining Joust, Stargate, Robotron and Bubbles. Two circuits have to be added to the ROM board: a clipping circuit for the blitter chips and SRAM in place of the Dxxx EPROM. Also, the control interface board has to be modified slightly.

Thanks go to Lee Crawford for his excellent joystick hack.

Digital Eclipse presents Williams Digital Arcade

Digital Eclipse (510-450-1740) has released three classic Williams games on the Macintosh. Defender, Robotron and Joust are exact duplicates of the original games because they use the real ROM images, running on an emulator.

The games start out with the 'rug' RAM test, then 'All Systems Go'. You can even enter the Bookkeeping mode and Setup screen. High scores and game settings are saved to a disk file between sessions.

I purchased Robotron, and am quite pleased with it. It was $30 with shipping. I was surprised to find out that it comes with the older (yellow w/orange stripe) ROM image, since I heard that Joust comes with the newer, non- 'pterodactyl bug' ROM image. (It was easy to hack the Joust ROMs into Robotron, though!)

Game play is pretty good on my 40MHz 68040 machine, especially in 16 color mode. Since all the Williams games only had 16 colors, 256 mode is overkill. With a 480-line or taller display, you can double the pixel size to make the game normal sized. Otherwise, it's kind of hard to see what's happening.

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