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zig-zag PCB tracks, what are they for?

Discussion in 'Electronic Basics' started by ErikBaluba, Nov 1, 2005.

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  1. ErikBaluba

    ErikBaluba Guest

    Hi,

    I sometimes see zig-zag copper patterns on some PCBs. What is the purpose of
    these?

    Example, I have a PCI I/O card where there is a copper-track that make nice
    symmetric and repetitive half turns from the I/O chip to the CLK signal on
    the PCI slot.

    erik
     
  2. Don Bruder

    Don Bruder Guest

    Even though signal propagation is faster than you and I will ever see
    with our own eyes (since they're too slow) it isn't instantaneous. Add
    length to a trace, and you add to the time it takes for a signal to get
    from one end of that trace to the other. The amount of time added per
    unit of length can be calculated accurately, even though it can't be
    directly observed easily.

    What would this suggest to you in relation to a CLK signal?
     
  3. Ben Jackson

    Ben Jackson Guest

    It's called "tromboning" and it's to extend IO lines (usually to length
    match).
    The "PCI Local Bus Specification" (not freely available, unless, of course,
    you google for that exact phrase) says (v2.1, section 4.4.3.1, "Trace
    Length Limits"):

    The trace length for the PCI CLK signal is 2.5 inches +/-0.1
    inches for 32-bit and 64-bit cards and must be routed to only
    one load.

    If you're making an experimental PCI card you can get away without
    meeting those specs while you play around in your home pc...
     
  4. Guest


    Having recently done some PCI designs, I would highly recommend that if
    anyone is building a PCI card, they adhere strictly to the layout
    specifications, or you may find that your project doesn't work.


    YMMV

    Mark
     
  5. John Fields

    John Fields Guest

     
  6. Deefoo

    Deefoo Guest

    The original post is from November 2005. Did it take you six months to come
    up with this lame joke?

    --DF
     
  7. John Fields

    John Fields Guest

     
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