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Re: [midatlanticretro] Re: vintage SRAMs self healing

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  • Dan Roganti
    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
    Message 1 of 18 , Nov 14, 2012
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      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. So that you will have a good baseline to work with. I don't think it's a complete kludge :) but you really like to have a solid working platform. Yours can can be done with some minimal steps - it's the same wiring but now you have to solder them :) You can dedicate a type of daughter card which would hold the Ram test socket -- or dedicate the whole Superproto card as a tester. The daughter card would plug into the top(or rear) of your SuperProto card. You can wire a generic I/O interface on the SuperProto card from the 6522. Use some right-angle headers/connectors to mate the two on top of the SuperProto card. Have one daughter card dedicated for the 2102 and another for the 1101.

      The important issue is to keep the wiring short, point to point, use plenty of ground pins on the headers/connectors - the typical layout is to alternate the signals with grounds along the headers pins to reduce Crosstalk - and having plenty of ground pins helps to avoid Ground Bounce when many signals are switching simultaneously on the bus. Since there's a minimal amount of passive components on there, you can improve the quality even further prior to adding the Ram tester circuit on there. Create a ground plane on there using the grid of plated through-holes - say a grid with a gap of 300mils and connect each side of the grid straight to the ground bus.  The more pcb area thats covered with a ground plane improves the signal integrity.

      BTW, the capacitance on a ribbon cable is not any significant amount higher than a FR4 PCB - approx 2pf/inch vs 1pf/inch. Ribbon cables have been used everywhere for the past 40years on boards fatter than my butt. It's all in how you organize the signals. This is where you reduce the crosstalk/signal intergrity issues.
      Dan

    • s100doctor
      ... Create a ... 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,
      Message 2 of 18 , Nov 15, 2012
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        --- 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
      • 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 3 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 4 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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