In 1983, the home video game console market crashed bringing many companies to fold. After the dust settled, Nintendo emerged as a phoenix from the flames with their iconic Famicom, known outside of Japan as the Nintendo Entertainment System (NES). The NES went on to sell in excess of 60 million units and brought about the third generation of console gaming. The success in 2016 of the NES Classic goes to show how popular the console and its games still are. While it may not have been obvious at the time, understanding the scope of IP rights may have helped to make this possible.

For the aspiring home console manufacturer in the early 1980s, there were really only two options when considering what microprocessor to use. The first option was the Zilog Z80, most notably used by the ColecoVision and the Sega Master System. The second option was the MOS Technology 6502, which was being used by the Atari 2600 (in the stripped-down form of the 6507), the Commodore 64, and numerous arcade games. When Masayuki Uemura, then head of Nintendo's R+D2 team, was presented with these options whilst developing the Famicom, he opted for the 6502. Although an official justification for this choice has never been given, a cursory glance at the patents for the two chips reveals that the decision may have been driven, at least in part, by patent protection.

Reverse engineering in action

When the NES finally hit US shores in October of 1985, very little was known about the technical specification of the console. All that was known was that the NES was powered by a hitherto unknown processor called the Ricoh 2A03. The most notable thing about the 2A03 was that its instruction set was almost identical to the 6502. Put another way, if you could program for the 6502, you could program for the 2A03. But the 2A03 wasn't a 6502, if it was then Nintendo would have had to get some kind of agreement from MOS Technology in order to use it. No such agreement was in place.

This perplexed the engineers at Commodore, MOS Technology's parent company and maker of one of the NES' rivals - the Commodore 64. In all respects the NES' 2A03 chip appeared to be a 6502, but Nintendo hadn't obtained a license for using a 6502 and it would have been unheard of for Nintendo to use the chip without MOS' permission. So the Commodore engineers applied the "Duck test" - if it looked like a 6502, acted like a 6502, responded like a 6502, then it probably was a 6502.

They started by examining the guts of the processor. To do that, they needed to carefully strip away the outer layers of the chip to reveal its inner circuitry. When they finally stripped the layers back, they saw the familiar circuitry of the 6502 but with one key difference - part of the processor had been physically disconnected. The circuitry was still there on the chip, but the control lines to that circuitry had been cut. This meant that the chip would operate as expected, with the exception of any instructions that used the disconnected circuitry. Upon closer inspection, it became apparent that the disconnected circuitry corresponded to the logic required for the chip's binary-coded decimal (BCD) processing.

In essence, BCD allows for decimal numbers to be added or subtracted by the 6502. This seems like a completely trivial piece of functionality, but without it, programmers were limited to representing numbers purely in hexadecimal or binary. Allowing programmers to use decimal mode (via the BCD processing), can greatly simplify some programming tasks.

While it’s difficult to say for certain, the main reason that Ricoh and Nintendo chose to make this small but significant modification to the chip’s design was probably to avoid patent infringement, as BCD functionality was an integral part of the original 6502 patent.

The scope of protection offered by the 6502's patent related solely to the BCD functionality. Remove that functionality, as Nintendo and Ricoh did, and you avoid patent infringement.

So, the reason for Nintendo choosing the 6502 may have been driven, at least in part, by IP considerations. As a result, Nintendo was able to produce a microprocessor for its console whose instruction set was well known to game programmers, without needing to pay any licence fees for the product.

Should they have seen it coming?

To understand the reasoning behind the focus of the 6502's patent on BCD functionality, you need to know what MOS Technology's target market was - calculators and home computers.

MOS Technology, prior to being purchased by Commodore, was not focussed on developing chips for games consoles. The 6502 had found its way into the Atari 2600 (as the 6507) but games consoles were hardly the 6502's main users. Their primary markets were calculators and computers. So, holding a patent for a processor capable of performing BCD functions with ease was a good patent to hold as it would cover their main commercial interests.

When you consider what the Nintendo engineers did, it seems that the 6502 patent is too narrow in scope. However, would it have been conceivable to cover such an eventuality? The thought that a company would go to the lengths that Nintendo did to remove the BCD functionality would have seemed absurd. Atari had licensed a stripped-down version of the 6502 for their 2600 console, and a range of home computers were using it. So, for the Commodore and MOS Technology engineers at the time, why would a company do any different?

Current Protection for Microprocessors

So what stops this kind of patent avoidance happening today?

Today, IP protection for integrated circuits (ICs) is far more mature than it was in the late 1970s and early 1980s. Back then, circuitry such as that of the 6502 was only covered by patent protection. That is, it was only the functionality of the circuitry that was protected commercially. However, functionality is only half of the story; the design of the IC is also important. If MOS Technology had obtained some kind of protection for the design of the 6502, it may well have been able to take legal action against Ricoh and Nintendo for the production of the 2A03.

The Washington Treaty 1989 sought to overcome these problems by providing protection for the layout design of integrated circuits. Although never ratified, the treaty has been partially integrated into the TRIPS agreement (see Article 35 of TRIPS). Whilst Article 35 of TRIPS is rarely used in practice, it is still a useful form of protection available to IC designers. In addition, EU directives confer further protection for the "topography" of semiconductor products, and so protection for an IC is now given to its layout-design and final form, as well as the protection inferred by a patent.

Today, the increased complexity of microprocessors, and the more rigorous IP protection available, makes it almost impossible to repeat Nintendo's reverse engineering feat. However, this story highlights the companies to have a holistic view of intellectual property protection in all its forms. Patents are just one part of the picture and a multi-layered approach will provide more robust commercial protection.

Bibliography

Footnotes

* Image is made available under a Attribution-Noncommercial-Share Alike 2.0 license. Image available at https://www.flickr.com/photos/28896521@N03/23179974993.