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Some questions about a Nubus card in an Apple II

Discussion in 'Electronic Design' started by Eeyore, Jun 2, 2007.

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  1. Eeyore

    Eeyore Guest

    I've got another request for help with some 'antique' kit.

    The equipment in question uses a Nubus interface card to communicate with the
    software on an Apple II.

    Thse 'interface cards' have a fair bit of local intelligence, in fact there's a
    whole 68020 @ 16MHz on it with a shedload of I/O.

    The problem that's typically experienced is that the host platform / software
    fails to recognise / talk to this 'interface'. There seems to be no special
    rhyme nor reason to it, aside from the fact that they gradually fail, with
    resets becoming more and more often required to get things working until
    eventually there is no response at all.

    One thing that caught my attention was the use of 74ACT651 interface
    transceivers on this card. I was puzzled about (a) the use of 'A' series - it
    seems that Nubus rarely ran faster than 10 MHz and (b) the use of 'T' parts
    since almost all the other generic logic on the card is 74HC.

    I have schematics btw but no other accomanying documentation, test procedures or
    test software.

    Initially I plan on checking for obvious stuff like the presence of suitable
    power-on reset signals and any obvious bus conflicts.

    The company whose product it is supplies a $5000 'refurb' board on receipt of
    the old one but this would only make sense if the equipment had commensurate
    value today which it hasn't at those prices.

    Any comments ?

  2. Donald

    Donald Guest

    I don't think the Nubus was used on the Apple II.
  3. Eeyore

    Eeyore Guest

    Silly me. I meant the Mac II of course. I can just remember the Apple II as well. II-e
    in fact..

  4. Lionel

    Lionel Guest

    It wasn't. The old Apple II had an extremely simple 8 bit bus.
    The Wikipedia page has a link to the official Nubus spec's, which
    presumably include data on the correct logic levels on the bus, &
    maybe the recommended logic family for the bus drivers:

    I suspect that Graham's on the right track WRT to his comments about
    74ACT vs 74HC logic, as I've seen many similar problems in mixed logic
    family circuits over the years. Random failures that increase with the
    age of the system are the classic symptom of that particular design
    (or manufacture) error.
    I'd first scope out the logic levels between the ACT drivers & the HC
    main logic inputs, as that's the point of biggest mismatch between C &
    TTL spec's.

    \___ Proud Cog #1 in the AUK Hate Machine
    _(AUK)====:: Do *you* think that you have the Right Stuff?
    /='='='='-, Apply TODAY by addressing a gratuitously cruel
    (O+O+O+O+O) flame to: "Uncle Fester", C/O & AUK.
  5. joseph2k

    joseph2k Guest

    It has to do with drive levels to match nubus. Try swapping them out for
    AHCT parts. They have better endurance properties.
  6. Eeyore

    Eeyore Guest

    That's what I was wondering. The Nubus drive level is only guranteed to be TTL
    level I suppose ?

    AHCT ? Hmm, I've never some across those before - or have I ? Hmmm... Looks
    pensive and wonders where that memory card reader/writer I designed 15 years ago
    got to. BCT rings a bell too.

    Endurance ? In what way ?

    Many thanks, Graham
  7. whit3rd

    whit3rd Guest

    Nubus was made to be self-configuring, and each addressable
    slot has unique ID. You can use utilities to find out what cards are
    in what sockets (and this would be a first step if 'talking' isn't

    Also, each card has its own ROM for ID and autoload of drivers; if
    card's EPROM is losing data (not unlikely at this date, Nubus was
    used 1986-1995), that could be messing things up the way
    you describe. If you can, try to locate/remove/read the EPROM
    and program a new one.

    Heck, if it's in a socket, just yank it and reinsert (to clean the
  8. Eeyore

    Eeyore Guest

    Utilities ?

    The Mac world seem devoid of anyone technically competent in such matters.

    I have 2 of these boards and the code EPROMs match. I can't see any ID ROM or
    EEPROM on the schematics.

    Done that. No help sadly.

  9. joseph2k

    joseph2k Guest

    Better ability to survive voltage or current excursions on the I/O pins
    outside normal operting conditions.
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