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Parallel port question?

Discussion in 'Electronic Design' started by Fred, May 2, 2005.

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  1. Fred

    Fred Guest

    I just wonder why a measure 3.36V (instead of the 5V - TTL) on the
    data pins of my parallel port (I put my voltmeter directly between the
    data pin #0, set to logical 1, and the ground)?

    I'm sure I forgot something but I appreciate if someone can help me.
  2. John  Larkin

    John Larkin Guest

    3.36 volts is a legal, and fairly ordinary, TTL high level. True TTL
    drivers never did pull all the way up to +5.

  3. Joerg

    Joerg Guest

    Hello John,
    This must be a pretty old system if it has TTL chips in there instead of
    CMOS. Probably right after the abacus and the slide rule calculator
    (which I am still using...).

    Regards, Joerg
  4. John  Larkin

    John Larkin Guest

    Perhaps so, but 3.36 is still a legal TTL high. Classic TTL parts were
    usually specified for a min Voh in the 2.5-2.7 sort of range, and typs
    around 3.4.

    Slide rule? How dated! I use an HP-35.

  5. My laptop gives almost exactly 3.3 V. I would bet that it's 5 volt tolerant
    3.3 volt CMOS.

  6. Joerg

    Joerg Guest

    Hello John,
    Ok, I also use an HP-11C. But when I have to calculate RC, resonant
    circuits, filters or stuff like that I sometimes crack out the old slide
    rule calculator. This speeds up the calcs when I want to stay within a
    range of already released part values or within a standard series. It
    does raise eye brows at times. At one client they reminded me that they
    do have Edison electric light.

    Regards, Joerg
  7. Ken Taylor

    Ken Taylor Guest

    As John has implied, the spec actually stated that it was to be TTL voltage
    levels on those pins.

  8. Yes, but 3.3 V CMOS will produce legal TTL levels.

  9. Si Ballenger

    Si Ballenger Guest

    It is probably the design of your motherboard. Probably a 3.3v
  10. Ken Taylor

    Ken Taylor Guest

    Yes indeed. I think we've all satisfactorily surrounded the answer from all
    directions and can go home happy. :)


  11. Pooh Bear

    Pooh Bear Guest

    Maybe you have a 'retro' chipset that emulates TTL levels ? There isn't a
    'toob' in there as well is there ? ;-)

  12. John Larkin

    John Larkin Guest

  13. Pooh Bear

    Pooh Bear Guest

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