Atari 2600 emulator for the VIC-20

Last Updated on March 5, 2024 by Dave Farquhar

Rumored to exist! I first heard the rumor in 1996, and more than a quarter century later, it’s never turned up. But let’s talk about the Cardapter 1 and the Game Loader, a pair of vaporware Atari 2600 emulators for the VIC-20. The Cardapter 1 was  demonstrated in January 1983 under much secrecy, advertised a bit over the spring of 1983, but never appeared. The Game Loader is a bit more mysterious.

Cardco’s 1983 announcement

In the Spring 1983 issue of Commodore Power/Play magazine, on page 99, Cardco’s Atari 2600 emulator appeared in the New Products section next to various other VIC-20 products. The VIC-20 was still the most popular computer on the market at the time. Marrying it with the most popular console of the time probably seemed like a good idea. And Cardco was one of the biggest makers of accessories for Commodore computers.

Cardco had a prototype at the January 1983 Consumer Electronics Show. The April 1983 issue of Creative Computing described it as being available for demo in a hotel room with a rent-a-guard at the door. By their account, on page 43 of the magazine, it was housed in a taped-together orange cardboard box and used the VIC’s function keys for select switches to control the games and replicated the VIC’s cartridge port so you could still plug in VIC cartridges as well. “The whole thing works like a charm,” the account concluded.

And the name Cardapter 1 implied there might be more forthcoming. Tantalizing!

So there was a bit of a splash in the spring, between the new product coverage and the ads. But within a few months the ads disappeared, and then we never heard of it again, at least until Atari collectors in the 90s found those old ads.

Times were changing fast in early 1983. I don’t think the product ever reached production. Ads for the product never showed any hardware, just the packaging, if anything at all.

How it would have worked

Although the VIC-20’s 6502 CPU is fully compatible with the Atari 2600’s 6507 CPU, the adapter would have had to have its own CPU. There were two reasons. First, the clock speed on the 2600 was 1.19 MHz while the VIC ran at 1.02 MHz.

The 2600 famously depended on the CPU for much of the graphics work. Since it lacked a frame buffer, the CPU has to draw the screen line by line, and consume exactly 76 CPU cycles. Since the VIC-20 runs its CPU at a slower speed, its CPU comes up 10 clock cycles short. This wouldn’t just cause games to run slowly. It would cause the graphics to glitch as each scan line wrapped around onto the next line.

So while it would seem that emulating the 2600 would be easier on a VIC-20 than on systems that used a different processor, it ends up being no easier. The timing issues mean there’s no getting around putting a CPU on the cartridge and running it at 1.19 MHz.

This also solves the other problem: the memory map was too different between the VIC and the Atari 2600. The VIC cartridge port has two I/O address lines that could host the necessary chips, but they live at the top of memory, at $9800-$9BFF and $9C00-$9FFF. Atari put the TIA at address $0000-$003D and its 6532 RIOT at $0280-0297.

There’s also something special about the memory locations. On the 6502, the first 256 bytes of memory are significant. It’s a special area of memory called the zero page. The processor can address the zero page in fewer cycles than the rest of its memory space. So you can’t just put the TIA where the VIC has room, then copy the cartridge into RAM and patch it. The patch would throw the timing off.

There was also no getting around the other two chips. The Atari TIA is completely incompatible with its VIC equivalent. The Atari’s RIOT chip has similarities to the 6522 VIA in the VIC. But the two parts aren’t completely compatible or interchangeable, and it lives at the wrong memory address.

So the adapter would have been basically a full Atari 2600 clone in a cartridge that just used the VIC for power and to replace the toggle switches. With no way to pass the audio and video through to the VIC, the cartridge itself would have had to handle video passthrough too, by plugging into the VIC’s A/V port and then providing its own A/V output that would go to your TV or monitor. Like Coleco’s module, it would have had to have its own joystick ports. It could have become as unwieldy as the ill-fated Spartan Apple II emulator for the C-64.

Why I don’t think the Atari 2600 emulator for the VIC reached production

Suitable chips existed, which is why they were able to display a prototype in January 1983. VLSI produced a clone of Atari’s TIA chip, which they sold to Coleco and Mattel for use in their own Atari 2600 compatibility products. The 6532 and 6507 were no problem to obtain. Various companies, including Commodore’s own MOS subsidiary, could supply them to Cardco.

Atari sued Coleco successfully, with the two companies settling about two months after this product was announced. Coleco could continue selling its Atari compatibility products, but it owed Atari royalties. Presumably Cardco would have to negotiate a similar arrangement, which may or may not have been feasible, and would have made the product more expensive.

But then the video game crash of 1983 happened later that year. The VIC gave way to the C-64 as the bestselling home computer later that year as well. The Cardapter 1 started to look like a solution in search of a problem, an $89 product with no market. Cardco never announced its cancellation, they just stopped advertising it.

It’s possible some examples of preproduction hardware exist in someone’s garage or basement in Topeka, where Cardco was headquartered. It’s also possible any hardware was long ago pillaged for parts for other projects.

The Protecto VIC 20 Game Loader

In 1983, Protecto Enterprizes (sic), a Commodore mail order dealer based near Chicago, advertised a similar product it called the “Game Loader,” priced at $79. Even though their ads sometimes said “factory direct,” Protecto was a distributor; they didn’t make their own products. But they had a habit of negotiating deals that let them sell private label versions of other products from other firms, which gave both companies leverage when someone asked them to price match.

There’s every reason to believe the Game Loader was also vaporware. For that matter, it probably would have been a relabeled Cardapter 1. It’s all circumstantial evidence but the dates line up. Both products appeared and disappeared at the same time, and Protecto had a long history of selling Cardco products. It’s likely they leveraged that relationship.

There’s been some speculation that Protecto may have been liquidating a closeout. I don’t think that’s the case here; their ads were running during the same timeframe as Cardco’s ads. What was in it for Cardco? Protecto had existing relationships with some video game magazines, having sold APF MP1000 game consoles in the 1980-81 timeframe, so this was a way for Cardco to extend its reach.