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This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

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Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Rule 5: Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

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New user moderation

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Has anyone found a strange acting NEC 8080 in an early IMSAI

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    Has anyone found a strange acting NEC 8080 in an early IMSAI

    In the spring of 1976 I sold some IMSAI 8080s that were included in my initial order from them when I became a dealer in early Feb. 1976. One of them went to a man named John Clarke in Shamburg, IL. (who a little later opened The Data Domain of Shamburg. one of the more successful computer stores started in 1876). John was an engineer from Motorola, and a very nice guy and a smart cookie.
    He called me one day to tell me that the 8080 chip in his computer was bad. I said that we wold call IMAI and see if there were an more bad ones around and get a replacement. A day or so later he called me again to tell me that the problem was in the design or prodction of the NEC 8080 chip, because he could prove that under certain instruction sequences one instruction failed and cause calculation errors. I don't remember what instruction it was, but he was right and NEC had to redo their maskand replace all of the 8080s made up to that time. So, if you have an early IMSAI and it has a NEC chip you might have a rare one indeed! One of these days I'll look him up again and ask him for details.
    Pioneer Purveyor of Personal Processing Power

    #2
    Re: Has anyone found a strange acting NEC 8080 in an early I

    Originally posted by olddataman
    In the spring of 1976 I sold some IMSAI 8080s that were included in my initial order from them when I became a dealer in early Feb. 1976. One of them went to a man named John Clarke in Shamburg, IL. (who a little later opened The Data Domain of Shamburg. one of the more successful computer stores started in 1876). John was an engineer from Motorola, and a very nice guy and a smart cookie.
    He called me one day to tell me that the 8080 chip in his computer was bad. I said that we wold call IMAI and see if there were an more bad ones around and get a replacement. A day or so later he called me again to tell me that the problem was in the design or prodction of the NEC 8080 chip, because he could prove that under certain instruction sequences one instruction failed and cause calculation errors. I don't remember what instruction it was, but he was right and NEC had to redo their maskand replace all of the 8080s made up to that time. So, if you have an early IMSAI and it has a NEC chip you might have a rare one indeed! One of these days I'll look him up again and ask him for details.
    It is indeed true. The first NEC D8080 was built from spec not a mask copy and like many other Intel products to follow the spec lied. NEC
    would quickly follow up with the uD8080AF to correct that. From then on
    ALL NEC micros that were not mask exchange were tested and certified
    exact functional (8085, D780(z80), 8088, 804x, 8051) even V20 that is an improved 8088 with 8080 compatability mode is still fully socket compatable and binary compatable (but a bit faster) then 8088.

    I have examples of both NEC 8080s and they are mostly interchangeable except for some oddities around status flags and handeling of the halt/hold
    states.

    A side note is that the Z80 would revisit the PV flag issue. So some old 8080 code on Z80 too.


    Allison
    Good, Fast and Cheap pick any two.

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