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After reading about the Apple //e diagnostics card, I noticed on the screenshot below that it reports a CPU test and that the microprocessor is OK:

APPLE //e DIAGNOSTICS SCREEN

So I'm curious did the PROCESSOR TEST actually do anything? One would think that if the computer got far enough to boot the diagnostics and display the screen, then the CPU MUST be OK, right? Or is there something that it attempted to do to validate that the CPU was indeed OK?

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  • Shouldn't the a priori assumption be it does something? – dashnick Nov 5 '19 at 23:10
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So I'm curious did the PROCESSOR TEST actually do anything?

AFAIR it's exactly the same as loaded from the diagnostics disk. It runs a bunch of subroutines, each testing several instructions. All NMOS instructions are tested, none of the CMOS additions (*1).

One would think that if the computer got far enough to boot the diagnostics and display the screen, then the CPU MUST be OK, right

For one, there isn't many code until the card gets booted by the Autostart ROM - and not all instructions are used until then. I wouldn't wonder if it's less than 30%. Keep in mind, there are ~160 different opcodes - plus decimal mode for all ADC/SBC to be testet.

Or is there something that it attempted to do to validate that the CPU was indeed OK?

As said, it calls up all instructions and verifies the results.

*1 - The original Apple II, II+ and early IIe had an NMOS 6502, while the later IIe and all IIc used a CMOS 65C02 which offered additional instructions. AFAIK the CPU tests have never been extended to cover the new instructions.

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  • I know NMOS and CMOS as types of semiconductor, but I'm guessing they mean something different in this context. – Wayne Conrad Nov 6 '19 at 20:26
  • @WayneConrad The original 6502 was implemented in NMOS. The later 65C02 was not only CMOS, but also had additional instructions (to be exact, there was also a Rockwell NMOS with this expanded instruction set, but it wasn't much recognized in public). There were also various CMOS instruction sets, but for most cases its simply about the 65C02. The Apple II, II+ and early IIe were delivered with an NMOS CPU, while later IIe and all IIc were delivered with a 65C02. Above software got AFAIK never adapted for the CMOS version - that's the long version of that sentence :) – Raffzahn Nov 6 '19 at 21:07
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    I suspected something like that. I guess I should ask my question in... er... a question so you can post that comment as an answer :) Thanks for the explanation! – Wayne Conrad Nov 6 '19 at 21:15
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    No, no, nothing like that. What I mean is, the little question I asked in a comment got, from you, a comment that is a really good answer in itself. So perhaps I should ask my question as a real SE question, so that your comment could become a real answer, get an up-vote, and all that. Sorry, it sounds confusing even when I try to explain it. – Wayne Conrad Nov 7 '19 at 13:32
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    @WayneConrad Ah, ok. Got it. Well, na. Better come up with another one giving me a real hard time to answer :) – Raffzahn Nov 7 '19 at 20:46

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