Build an 8-bit CPU from scratch | Hacker News Reader

Build an 8-bit CPU from scratch

eater.net

54 pointspunnerud19 comments

https://news.ycombinator.com/item?id=21902281

Also, from 2017:

https://news.ycombinator.com/item?id=14883776

https://news.ycombinator.com/item?id=14450945

Ben Eater's pedagogy is top-notch for sure. But there are others out there. One worth noting is James Sharman[1] who has constructed a completely new, self-designed 8-bit CPU that features a two-stage instruction decode pipeline, and is currently adding scratch-built peripherals to it.

[1] https://www.youtube.com/c/weirdboyjim

I really appreciate Ben Eater's production values. He doesn't gloss over mistakes, but it's not just a direct recording of experiments. His videos have a definitely planned direction and it makes it much easier to watch.

Another cool project is the Magic-1 [1], which is also well documented. It even runs Minix!

[1] http://homebrewcpu.com/

Anyone's got an idea why the 6502 is more harder to find than the Z80 ?

Can't find them at any of my local electronics stores where i live for some reason unlike the Z80s which i find plenty of.

I think the 6502 was less 'general purpose' than the Z80 (which I've seen huge banks of in Honeywell FEP's, years ago, f.e.).

I imagine they're similarly sought-after now, though. I've never played with the Z80, so I don't know if it offers easier integration with arduino / RPi and other basic systems now.

FWIW I see they're available on local ebay for few dollars:

https://www.ebay.com.au/itm/273461107051

(I think the 6502A means it runs at 1.5MHz, but don't quote me on that.)

Yikes. That's a remarked part -- the style of printing on the top is wrong, and the date code is nonsense. (0448 would indicate it was manufactured in late 2004, but Rockwell Semiconductor was spun off as Conexant in 1999, and they stopped manufacturing this part many years before that.)

Oh, that's interesting (and way outside my knowledge bubble). You reckon it would actually work as a 6502, or it's remarked from an entirely not-65xx CPU?

There's a decent chance it's actually a 6502, but the actual part that's under those markings could be any one of a number of 6502s from many different manufacturers.

Both are possible. I guess there's a 70% chance that the chip is not a 6502 at all, nevertheless still a 30% chance that the chip is salvaged from trash and remarked but its silicon die is authentic.

> I think the 6502 was less 'general purpose' than the Z80 (which I've seen huge banks of in Honeywell FEP's, years ago, f.e.).

Z80 has more registers than a 6502, plus that built in dram refresh was nice to have. They're still useful for quite a bit, which may explain why you can still find Z80 parts on digi-key.

You can still get brand-new 65c02s and related peripherals as well.

The 6502 was as general-purpose as anything else. WDC still makes them, although you'd probably want the 65C02, which can also do a Vcc of 5.0 or 3.3 volts.

I think z80's are more popular in home-brews because there's a ton of free(-ish) CP/M software out there that can easily be used.

What's the legal situation of the 6502? Would there be risks in making them at scale?

The 6502 has a patent on decimal addition (#3,991,307), but that's long-expired. MOS Technology got sued by Motorola for making the 6501/6502 because they violated Motorola's patents on the 6800 and took trade secret documents.

IC masks are protected as of 1984 (mask work is essentially copyright for the die), but the 6502 predates that.

Some companies (such as Intel) copyright the assembly-language mnemonics, but that wouldn't be an issue.

I can't think of other issues with the 6502 but I'm not a lawyer. Note the MOnSter 6502, a copy of the 6502 built from discrete transistors. I should also point out Ben Eater's 8-bit CPU is a simple design, not a 6502.

IC masks are protected as of 1984 (mask work is essentially copyright for the die), but the 6502 predates that.

...and the copyrights for masks are much shorter than traditional copyright - only 10 years in the US: https://en.wikipedia.org/wiki/Integrated_circuit_layout_desi...

Well, Ben Eater isn’t the one making them, but Western Design Center (WDC, no relation to WD) who supposedly owns the rights to produce them. Eater is just reselling them which is allowed under the “first sale doctrine”

> Western Design Center (WDC, no relation to WD) who supposedly owns the rights to produce them.

The founder of WDC, Bill Mensch [0], was one of engineers from the original 6502 team at MOS Technology.

[0] https://en.wikipedia.org/wiki/Bill_Mensch

Well that certainly explains it. I never knew that

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