But TTL isn't an option, Ed. A 65xx CPU will be either MOS or CMOS, and in both cases the inputs are mostly capacitive, as you say.

@socram, I think it would be best to double check your conclusion, just in case something else is causing your program to fail. How about trying the following? This should loop even on an NMOS CPU.

cheers
Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

D'oh! If only I could pretend I was bluffing for comedy effect!

The electrical difference, then, would be the characteristics of the output drivers... but would be fairly subtle. I'd expect CMOS, with a PMOS pullup, to have the better/faster/stronger pullup.

When I am revealed to have slipped up I blame it on lack of coffee -- a missed dose of caffeine. But in your case maybe the (missed) beverage of choice would be tea.

Alright, an excellent point -- you're redeemed. And the specs show the difference isn't all that subtle. MOS output drivers pull low ably enough, but are rather anemic in the high state. They don't reach anywhere near Vcc, and the available current is tiny.

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

(note only A15 and A2 to A0 are connected, thus 8004 above is RESET vector fetch)

They come from this seller: https://www.ebay.es/itm/-/171727464113

Alright, that is the behavior we expect. It certainly looks as if it's an NMOS 6502 you've got.

Is there any reason you can't use one of your CMD 65C02's instead? Really the NMOS CPU's have almost no advantage, unless you need to run programs that rely on NMOS behavior for the undefined opcodes.

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

From adeleparts2010? That's supposed to be an OK ebay seller. I'll be more cautious about what I buy from them in the future.
Please please give them a 100% negative feedback response. That's the only way that can get to them.

I bought 10 R65C02P4's from polida2008 a while back for $13. They've not arrived yet, but I'll let folks know if the are genuine when they arrive. The last time I bought off polida2008, they were good parts.

Here is the link.
https://www.ebay.ca/itm/10PCS-Microprocessor-IC-ROCKWELL-DIP-40-R65C02P4-11450-14-R65C02P4E/401500430834?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

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Bill

Dang, Bill, I hope you don't get ripped off, because the pictures provided by polida2008 at your link look a bit suspicious. How could the ones with identical build dates in 1993 look so different? And the one allegedly manufactured in 2006 ... did that come from the same Rockwell Automation factory as the Retro-Encabulator and the Write-Only Memory chips?

Mike B.

13 bucks seems awfully high for one of those MPUs, genuine or otherwise.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

It was $13 for all 10.

_________________
Bill

The two with '93 date codes were just photographed under different light (warmer vs. cooler). That '06 one does stand out. Well, it might just be a surprise bag... we'll see.

Just further note on this. When Rockwell international broke up in 2001, the automation and what was left of the semi-conductor fabrication along with the legal identity that was Rockwell International went over to Rockwell Automation (RA) and the rest of the semiconductor stuff went earlier to Conexant (circa '97). RA still do produce semi-conductors and ICs (but not for re-sale) and they do own the logo and name 'Rockwell International'. Conexant was eventually taken by Syanptics but had several spin-offs along the way. It's quite possible that a Rockwell branded 65C02 was manufactured in 2006. I know that is mere speculation, but has anybody got anything more than speculation to the contrary to say that some production did not continued?

_________________
Bill

Okay, that's a bit more reasonable.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Let me share my experiences with buying old CPUs at Ali & ebay.

65C816 from ali - doesn't work
UMC W65C02S from ebay - works ok, doesn't output VP signal - maybe laser-remarked 65C02.
MC68008 from ali at $1.1 - one with broken pin, otherwise all 3 are ok.
4 pcs. of. Z84C00 from ali at $.4 - proved to be remarked Z8400 (NMOS version). 4 different chips with the same laser marking incl. date code.
5 pcs. of NEC V20, HCZ-16 version - laser marking too nice to be true, albeit with 4 different date codes. To my surprise all chips are V20, probably C version, but all work at 3.3 V.
2 pcs. of MC68010 - too nicely laser-marked, two different chips with the same date code. Had no time to check. I suispect they might be MC68000.

1 pc. of ST Z84C00 from ali at $1.4 - looks like laser-remarked, but it really IS Z84C00!
2pcs. of WDC W65C816 from ali at $1.4 - the only ones not looking like they were remarked. AND THEY WORK OK!

Did you buy from sellers with 100% positive feedback? That's one way to try to limit the damage. AliExpress and eBay aren't outlets in the usual sense, with reputation, so you have to look at each seller's reputation. I think a seller will often give a refund in preference to getting negative feedback, in which case you can make a tradeoff: you lose some time, but no money, but you don't assist future purchases with the benefit of your bad experience.

Edit: in fact, I think you're more likely to get a replacement than a refund, assuming the supplier can set things right that way - that they actually have the part you want.

There are no sellers with negative feedback at ali.
As the only obvious case was with the Z8400 remarked as Z84C00, I immediately requested refund. Something strange happened then: on the next day, before I got any response from the seller, there was ali ruling about refund. I guess this was because I used the right keywords in my dispute: "false" and "counterfeit".