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1-wire specification

Discussion in 'Electronic Design' started by Raveninghorde, Jan 11, 2010.

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  1. I am using a DS2438 as a battery monitor. The app notes recommend a
    series 330 ohm in the DQ line for static protection. The data sheet
    shows 4k7 as the master pull up resistor.

    I have a Link45 serial to 1-wire interface and the cooms does not
    work. A quick check shows a 1k bus pull up. So the 330 ohm is not
    allowing the output from the battery to get lower than about 1.2V.

    Is there actually a specified min and max for the bus pull up
    resistor. I.m looking but haven't found a specification yet.
     
  2. Your math isn't too bad ;-)

    I am seeing Maxim app notes for 1-wire on long cables saying 1k may be
    needed. This of course doesn't work with the Maxim app notes saying
    fit a 330 ohm resistor for static protection. So it looks like I have
    to design for 1k pull up. Just wish I could find a spec giving min
    and max figures.

    Who writes app notes? Certainly no one who knows what they are doing.
     
  3. Mark Zenier

    Mark Zenier Guest

    Should be buried in the spec sheet somewhere. Dig, dig, dig ...
    ADI-1031, October, 1984.

    Compare the 6805P2 and 68705P3 "Port DC Characteristics" pages in the
    back. There's only one section for the 705P3 Port A characteristics.
    But for the P2, there are two. So find the one that's the best match.
    "Iih" for Port A in the 705P3 matched the characteristics of "Iih"
    for port A on the the P2 "with CMOS Drive Enabled". So, always enabled.

    Took me about 5 minutes to answer a question that's 25 years obselete. ;-)

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
     
  4. Mark Zenier

    Mark Zenier Guest

    I thought that's what I said. " But for the P2, there are two. "
    Meaning, they have two sections in the MC6805P2 (and 'P4 and 'P6)
    "Port DC Electrical Characteristics" table of the spec sheet, one
    for "Port A with CMOS Drive enabled", and one for "Port C and
    Port A with CMOS Drive Disabled". Giving VOL, VOH, VIL, and VIH
    under various conditions. The "drive enabled" section matches
    the '705P3' table in having both the additional "VOH with a 10 uA load"
    spec, and having the higher IIH spec.

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
     
  5. Jon Kirwan

    Jon Kirwan Guest

    Mark, I think your answer was tight and targeted at the OP's
    first post well. I think Asgard24's response tried to change
    the subject, writing "The point was that there should be a
    bit more clarity to begin with, not that the question
    couldn't be answered with some digging." That hadn't been
    the OP's point, but it was a point Asgard24 tried to turn it
    into for reasons I don't fathom well.

    You were right to write as you did. It was on point and
    nicely said.

    Jon
     
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