Hello

I have been confused for some time regarding patents and all the legal stuff about 65xx family so decided to ask.

How exactly legal it is to create emulators & fpga implementations of the cpus?
Last time i checked, WDCs website says that they provide licenses for fpga cores and such, so i wonder if open source fpga implementations are legal or not (as, well, some open source licenses would allow people to sell an fpga based 6502 that does not come from WDC)

This is just a shower thought of mine, but i just cant get it out of my head

It's completely legal and OK to create emulators and fpga implementations. (And TTL implementations!)

Of course it would not be OK to use WDC's specific cores without licensing them, or to use their support code without appropriate licensing.

Every idea in the 6502, 'C02, and '816 is now old enough that it is not protected, with the possible exception of any trademarks that WDC might have.

Whereas copyright in software has a disturbingly long life, the protected life of a patent or a mask design is much shorter.

So one might continue to fret about ROMs, operating systems, interpreters, games, there's no need at all to fret about the CPU.

As noted in other discussions, the practicalities of copying software are more murky, because many people are prepared to take the risk which they estimate as vanishingly low. But it would be good to keep that discussion in its own thread.

In general, patents have an enforceable lifetime of about 20 years. The precise date from which that period begins varies by jurisdiction, of course, but will always be somewhere between the earliest filing and the final granting. The 6502 was known to be covered by at least one interesting patent, namely its unique handling of BCD arithmetic; avoidance of that patent is the main reason why some 6502 clones don't support Decimal mode (notably the NES' and Tamagotchi's CPUs).

Since the original 6502 was in production from the late 1970s, and the CMOS versions from the early 1980s, any patents embodied in that vintage of hardware can safely be assumed to have expired circa 2000, more than 15 years ago. Even the current production models (which use a newer manufacturing process purely because the original one is no longer available) are highly unlikely to contain any patentable enhancements over 1980s models. Hence building both software and hardware clones based on the specifications or even the original hardware designs is completely safe from a patent standpoint.

Copyrights and trademarks tend to have a substantially longer lifetime than patents, and are covered by separate bodies of law.

(Worth noting that mask copyright is a special case: I think it lasts for just 10 years. So you could deprocess and photograph a suitably old chip, and make a copy of the layout, with only patents to worry about. A sufficiently old chip, and you don't even need to worry about patents. It's true that patents can be granted surprisingly late - they must be filed before parts are sold, but filing date and grant date are different things.)

Aha! That totally explains why I've seen "PATENT PENDING" stamped on products so many thousands of times over my lifetime.

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Got a kilobyte lying fallow in your 65xx's memory map? Sprinkle some VTL02C on it and see how it grows on you!

Mike B. (about me) (learning how to github)