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Re: vintage SRAMs self healing

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  • Mike
    HI, Boy, you guys are tough reviewers. :-) Other than testing speed, this test is about as complete as it can get. Signals look remarkably good, edges are
    Message 1 of 18 , Nov 15, 2012
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      HI,

      Boy, you guys are tough reviewers. :-)

      Other than testing speed, this test is about as complete as it can get. Signals look remarkably good, edges are fine with no ringing, overshoot or undershoot.

      The nice thing about this tester is how quickly I was able to put it together. 3 evenings for the 1101 tester and a couple of more hours to create the 2102 version. Directly interfacing to a processor would have taken considerably longer.

      The other interesting thing is that I tested 200 1101 parts, with only 1 part that I damaged during development of the test, failing.

      I'm currently investigating whether tarnish is a contributing factor.

      Regards,
      MIke W.

      --- In midatlanticretro@yahoogroups.com, "s100doctor" <hjohnson@...> wrote:
      >
      >
      >
      > --- In midatlanticretro@yahoogroups.com, Dan Roganti <ragooman@> wrote:
      > >
      > > Mike,
      > >
      > > I didn't see your link before and just took a look at your homebrew tester.
      > > It really needs some more work to tighten up the circuit before proceeding
      > > with further experiments.
      > > The important issue is to keep the wiring short, point to point...
      > Create a
      > > ground plane on there using the grid of plated through-holes...
      >
      > Dan, I don't know if you read my most-recent post, before writing yours. Even though I also mentioned crosstalk and noise and such - frankly, I don't think that matters, with this tester. He's using a bunch of latches under software control, to operate the RAM. It's going to run slowly enough, that any switching-around noise won't last long enough to matter - much. (I suppose there could be some situation where it does, if one worked at it.)
      >
      > Seems to me...if he's to go to the trouble of building a proper, ground-planed, short-wire fixture....he may as well design something that connects the RAM right to the processor, and run it at CPU clock speeds. That is, under design conditions.
      >
      > THEN all that stuff you describe, matters. And THEN, with such a real-use kind of tester, with "good" signals all around, then one can do some more serious testing, and draw more serious conclusions.
      >
      > Again - it's a reasonable bench-top, put-together-for-use, kind of tester. But to use it to make claims about "self-healing RAM" phenomena, I think is pushing its limitations.
      >
      > Herb Johnson
      >
    • s100doctor
      ... I largely agree with you - this is a nice bit of work. One could test most any bit of logic with variations of this Apple II code and hardware. And it s
      Message 2 of 18 , Nov 16, 2012
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        --- In midatlanticretro@yahoogroups.com, "Mike" <mike@...> wrote:
        >
        >
        > HI,
        >
        > Boy, you guys are tough reviewers. :-)
        >
        > Other than testing speed, this test is about as complete as it can get. Signals look remarkably good, edges are fine with no ringing, overshoot or undershoot.
        >
        > The nice thing about this tester is how quickly I was able to put it together. 3 evenings for the 1101 tester and a couple of more hours to create the 2102 version. Directly interfacing to a processor would have taken considerably longer.
        >
        > The other interesting thing is that I tested 200 1101 parts, with only 1 part that I damaged during development of the test, failing.
        >
        > I'm currently investigating whether tarnish is a contributing factor.
        >
        > Regards,
        > MIke W.

        I largely agree with you - this is a nice bit of work. One could test most any bit of logic with variations of this Apple II code and hardware. And it's not hard to do the same logic, with a Z80, a 6800, etc. It might be fun to use a microKIM, could even use most of your code! Plus, the microKIM could probably implement an at-speed tester too, plenty of address space "open". Even I, "the S-100 guy", have one of those.

        I'm curious...I think, reading your read/write subroutine, you are probably running the RAM at say 20-25 microseconds? Given an Apple II at 1MHz? If you looked at the signals, you probably know how fast your scope was sweeping to see one access time.

        I'm inspired to make something like this, if I get a Z80 prototype running next year. Thanks for keeping the 1970's on the bleeding edge again. Well....maybe the leaking edge.....;)

        Herb Johnson
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