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Power-On Reset

Discussion in 'Electronic Design' started by Jim Thompson, Feb 9, 2005.

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  1. For the simple reason that it was replying to something that had been
    posted to sci.electronics.cad.
    Perhaps your comments should be directed to the OP (?)

    Regards,
    Allan
     
  2. These were never reliable. Even in the '80s. :)

    Regards,
    Allan
     
  3. That reminds me of an 80c552 circuit I designed once. The Philips
    datasheet quite explictly stated that the port lines would go high
    when reset was asserted (and the clock was running!). But, as it
    turned out, that only applied while Vcc was within tolerance. When
    Vcc fell to about 2V or so, the outputs would go low, causing all
    sorts of mayhem.

    I fixed it by gating the port outputs with a 74HC part.

    Regards,
    Allan
     
  4. Paul Burke

    Paul Burke Guest

    If you want an example of someoone trying to get it von-chip, and the
    problems that resulted, look up the MSP430's brownout feature. It
    remains one of the poorer aspects of the design, and you still need an
    external reset if you really want it to be reliable. Which is a bugger,
    as this can consume as much current as the rest of the circuit put together.

    Paul Burke
     
  5. Jim Thompson

    Jim Thompson Guest

    I figured to find more ASIC designers on sci.electronics.cad than on
    S.E.D, only "flashers" hang out there ;-)

    ...Jim Thompson
     
  6. Ken Smith

    Ken Smith Guest

    Unfortunately I just caught a part holding its output high until Vcc was
    high enough to be taken as logic high by a 74HC part. I've had to add and
    and gate to the system.
     
  7. Guy Macon

    Guy Macon Guest

    Posting to inappropriate newsgroups because that's where the
    post you replied to happened to be is like shitting in your
    pants because that's where your ass happened to be. :)
     
  8. Rich Grise

    Rich Grise Guest

    That's what "followups-to" is for.

    And there is no alt.dev.null, boob.

    Cheers!
    Rich
     
  9. keith

    keith Guest

    I'll show you mine if you show me yours! ;-)
     
  10. keith

    keith Guest

    They are/were quite reliable if you know the power supply properties
    (or get to specify them). I've had many desings in places that the power
    supply sequencing, timing and slew was very tightly controlled (usually
    for other reasons). In controlled environments a fancy POR circuit is
    overkill and perhaps not possible.
     
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