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It's a few years old now, but still quite interesting to play with. The CPU itself is only 3.5K transistors but already looks amazingly complex until you visualise how it's broken down into individual, mostly independent modules:

http://forum.6502.org/viewtopic.php?t=2208&f=8

http://breaknes.com/

(The Russians seem to have a fondness for detailed IC reverse-engineering. There's a lot of Russian-only information on the internals of the 6502, 8080, 8085, Z80, etc.)

there's some interesting tech-related wikipedia pages which are more detailed and useful in the russian version (easily translated of course)
Examples?
https://news.ycombinator.com/from?site=visual6502.org

This has to be some kind of record for re-submissions.

And then there is a dis-integrated version, with a lot of LEDs that show how the chip works internally: http://monster6502.com/
GitHub repository: https://github.com/trebonian/visual6502
An interesting type of logic is DEC DTL "flip chip" technology, use in the original PDP-8. It uses all PNP bipolar transistors.

It's always interesting how they make flip-flops. In this case, the slave side is the typical latch made out of cross-connected inverters. The master side uses a diode-capacitor-diode gate. A capacitor follows the input signal. A pulse on the clock line transfers the charge to the slave latch.

http://bitsavers.trailing-edge.com/pdf/dec/handbooks/Digital...

There's also an ARM1 version, which is even cooler IMO http://visual6502.org/sim/varm/armgl.html

http://www.righto.com/2015/12/reverse-engineering-arm1-ances...

It's a bit of an evergreen without much in the way of comments.

https://hn.algolia.com/?query=Visual6502.org&sort=byDate&dat...

Any lawyers here? Are the architectures of those old microprocessors like 6502 or 8051 copyright/patent-free by now?

Can one create a commercial game where the players should reverse engineer programs for some virtual hardware which have, for example, a virtual 6502 on board?

Totally free and clear.

Copyright on maskworks -- that is, microchip designs -- only lasts 10 years. (It's covered by a unique and unusual portion of copyright law, as microchip designs aren't considered creative enough to be covered by a traditional copyright.) In any event, this would only have covered the physical design of the 6502, not its architecture.

The 6502 was released in 1975, so any patents on its architecture would have expired in the mid-1990s. I'm not certain that any such patents existed in the first place -- the 6502 is largely inspired by the Motorola 6800, which was even older.

Anyways, the architecture of the 6502 is effectively in the public domain at this point. There are probably thousands of different hardware and software reimplementations at this point; including one in a game would not be a problem at all.

Even though it is customary to throw a wide net when applying for patents, I also would think that chances are decent that any patents don't cover the embodiment of emulating the CPU on another CPU that's a few orders of magnitude faster, in an interpreted language.

Certainly (IMHO, I'm not a lawyer), any patents related to how to make the transistors, connects or the chip package in a 6502 wouldn't apply here.

Thank you (and others who answered). So, no copyright, no patents, and I forgot to ask about trademarks, but I think I can do without naming things for what they are if I ever go for my idea of that game.
As a number, "6502" was never trademarkable, and what was left of the original manufacturer (MOS) was liquidated in 2001. So there's no trademark rights either.
Keep in mind that Western Design Centre also has/had rights to the 6502, and they're still selling variations, so the fact that MOS was liquidated doesn't necessarily mean much.

But presumably you're right in terms of ability to trademark it anyway.

You can't trademark a number as Intel found with the 80486, which is why they went with the 'Pentium' name instead of with 80586 for the next release.
Liquidation might have moved those trademarks to a new owner.
IANAL but you may want to read https://en.wikipedia.org/wiki/Integrated_circuit_layout_desi...

and AFAIK the 6502 and 8051 have been around for long enough that any patents they may have had are already expired; the last time I looked up this info, the 486 subset was already patent-free, and the Pentium patents were soon to expire.

SuperH a microprocessor developed by hitachi in 90's, has many of their patents expired in 2015 and we are talking of technology used in Sega 32x and Saturn.

There is a clean room implementation, made open source https://en.wikipedia.org/wiki/SuperH#J_Core

For that purpose, an instruction level emulator would be far better than a transistor level emulator like this one.
this chip could cause pacman fever (pre RoHS)