Fun project! "Back in the day" there was a speedup for the PC/AT called the Chang Modification: when the CPU was executing an internal instruction, the clock was switched to a faster one since internal memory didn't require wait states.
I noticed that there was a pin on the MC6809E that indicated whether the current instruction was accessing external RAM or running from registers and realized that I could do the same thing. A Chang-modified CoCo2. However, I was young and had far more projects than I could get to. Most of which I never finished... 30 years later I still have the same problem!
Anyway, the challenge is open if you want to take it up :-)
> Absolutely remarked AliExpress parts, but I do wonder what these used to be.
And this, ladies and gentlemen, is why we validate our Supply Chain :-)
Nice project indeed. Just 1 nitpick - all vintage parts, and then a PIC uC just to generate a clock & reset? Grr.. ;-)
> And this, ladies and gentlemen, is why we validate our Supply Chain :-)
I've got a nice collection of vintage chips, and they're going nowhere. One reason being that with few exceptions, I know what type of equipment they were pulled (or hand-unsoldered) from. Mostly done by myself. Or that I have seen them in action, as in: tested, known good. Or have gear to test 'm in.
~15y ago it was relatively safe to order vintage parts online. These days, it's a crapshoot. You might get relabeled parts (different speed grades, NMOS vs. CMOS etc), parts where function of vintage IC is programmed into a gate array & packaged in original-looking housing (that may work but differ subtly from original part), random IC with markings changed that has no relation to what markings say (so it won't work & may even cause damage elsewhere when powered up), just housing + pins but no IC inside, etc etc. Anything is possible these days.
There are some nice YouTube video's diving down the "fake IC" rabbit hole.
Thing is, in many cases I wouldn't even mind buying a 'recreated' part as long as it's a functional replacement, and seller is honest about what's being sold. Or say, a slower speed grade if that fits requirements.
But it appears almost uniquely Chinese approach to just LIE about what's being sold. For example: the bulk of Z80's on eBay the 20 MHz version for like €1..2/pop, even though original part costs 10x that (yeah Z80's are still sold new !) and (cheap) pulled / "New Old Stock" parts will be 4..6 MHz parts with few exceptions? Yeah, right.
Vintage or relabeled, "who cares, it works?" seems the attitude. It's that lying I hate, not the less-desirable-IC in some subjective way. Sell whatever you want just be honest about what's in the box & how it was obtained.