Game Changer Interface

Clever hardware construction, both mechanical and electronic, and a solid comprehension of both 6502 (the Atari 2600 CPU) and Z80 programming combine to produce the very powerful “Game Changer Interface”. This unit cross-connects your Atari 2600 VCS and TS1000, allowing either to take control of whole blocks of shared memory. That “shared” memory includes the ROM inside the Atari game cartridge, and shadow copies of that ROM in the TS1000 RAM.

Using this system, you can download ROM games to your ZX/TS, disassemble the 6502 machine code, vary the game (or create a new one), and upload back to the 2600 to play the game.

Physically, the system consists of two double-sided plated through PC boards, professionally constructed. The mother board plugs into the back of the ZX/TS and connects via ribbon cable to the Atari VCS adapter board, which plugs into the VCS cartridge slot. A cartridge can plug onto the back of the adapter board.

Huron Valley’s mother board contains 4 HM6116S (2K Static RAMs) and uses some ingenious coding to remap internal RAM above their own 8K, for a total of 10K RAM in an unexpanded TS1000. The 4K above RAMTOP contains the actual VCS ROM image. This information moves to a 0 REM statement for manipulation by the ZX/TS machine; game execution can be accomplished by transferring the game code to the bottom of RAM and controlling the ZX/TS bus.

Menu driven software, supplied on cassette, includes two programs in BASIC and MC which download the cartridges (one for 2K and 4K games, one for 8K games), and a 6502 assembler and disassembler (to change the games). This feature comes in handy when you wish Atari had given you “just one more ship.”

This system works very well and even comes with high quality TV cables and a 3 way switch box for your TV set. You need that switch box, unless you use two sets, to switch back and forth between the VCS and the ZX/TS. I installed an extra RAM chip on the interface for an AERCO disk buffer and found the system completely compatible with the disk drive. With this combination I can download, save or retrieve any program in seconds.

If you don’t have a disk drive, however, things can slow down a bit. 8K game cartridges download into 10K BASIC programs, and we all know how long they take to load from tape. After you make or modify a game, you may want to have an EPROM burned. Since the system uses BUSRQ, dynamic RAMs (like those in 16K RAMpaks) will not work with it. Hunter’s ROM board, populated with 6116s, should work if everything decodes address line completely.

I had very little trouble loading the programs. The menus are simple and the documentation is Spartan. It consists of 7 photocopied typewritten pages, including an installation sketch and a hand drawn schematic, important memory map locations, and operating instructions. Perhaps the only flaw in an otherwise superb system, is the documentation.

Overall, while less than perfect documentation usually causes me to think twice, I rate the Game Changer highly. It is exceptionally powerful and well designed, and can provide the ultimate in inexpensive game play and design, for a total of less than $175 (including the price of the ZX/TS).