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power on firewire port ?

Discussion in 'Embedded' started by Robert Lacoste, Jan 13, 2004.

  1. There is power available on the 6-pin firewire connectors, but how much ?
    Does the standard gives a precise guaranteed minimum available power (shared
    by the slaves of course) ?

    Thanks for your help,

    Robert Lacoste - ALCIOM
    Robert Lacoste, Jan 13, 2004
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  2. Robert Lacoste

    Paul Black Guest

    Section of the 1394 spec details the power availability. In
    1394, a node could provide a maximum current of 1.5A with a maximum
    voltage of 40V. The self-id packets give detail about what a node
    provides and requires from a bus in terms of power. The 1394a spec has
    changed some of these values (e.g. max voltage is now 30V).

    There is no guarantee, however, that there is a node on the bus that
    provides power.
    Paul Black, Jan 13, 2004
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    That was the missing point for me : there isn't any guarantee that a node
    will provide power.
    So for example (in my case...) the developper of a Firewire peripheral, to
    be connected to a PC, can't rely on a power source from the PC at all, right

    Robert Lacoste, Jan 13, 2004
  4. Robert Lacoste

    Tim Clacy Guest

    Does it matter though? If you're unpowered, you will not get any bus events
    or messages; if you do get bus events or messages then you are powered.

    Some laptops only have a 4-pin 1394 port; these do not supply power. I'm not
    aware of any PC or Mac that does not supply power. For all intents and
    purpose, there will always be at least one power-provider capable node on a
    bus. Furthermore, you are allowed (assured of) up to 3W for the self-id
    phase where you should report how much power you actually require.

    There are three 1394 Trade Association specifications in connection with
    1394 power; you can order these on-line at http://www.1394ta.com/ and
    receive a PDF the next day:

    Power Specification
    Part 1: Cable Power Distribution

    Power Specification
    Part 2: Suspend/Resume Implementation Guidelines

    TA Document 1999001-3
    Power Specification
    Part 3: Power Distribution Management
    Tim Clacy, Jan 13, 2004
  5. Robert Lacoste

    Randy Howard Guest

    Apart from the aforementioned laptops.
    This is not true. There is nothing to prevent you from attaching a
    device to a notebook that expects power and not find it there. Ask
    me how I know. (It sickens me that nobody makes a notebook with a
    6-pin powered 1394 port anymore, it makes those ultra-small "drop in
    your shirt pocket" external drive carriers useful for notebooks in
    the field. Grrr. It's not exactly easy to plug in a wall-wart when
    you're in the middle of nowhere, with a notebook with plenty of
    battery power, but no 6-pin firewire. However, you can get PCMCIA
    1394 cards with 6-pin ports, but they really suck the power, and
    chew up an extra card slot.
    Randy Howard, Jan 14, 2004
  6. Well, that power-sucking aspect is quite possibly the reason why so
    many laptops refuse to power Firewire devices --- it just consumes too
    much of that most precious commodity in a laptop: battery power.

    In case of dire need, you could always use a USB external instead ---
    that's defined to always be powered by the host. If you use USB-2.0,
    you'll even get the same kind of speed as with 1394.

    Or, if you really want to stick 1394, there's bound to be some shop
    that makes a slave-power interface that connects to, say, both USB and
    1394 on the laptop side and uses those to provide powered 1394.
    Hans-Bernhard Broeker, Jan 14, 2004
  7. Robert Lacoste

    Tim Clacy Guest

    There's nothing power hungry about the FireWire bus itself; a powered,
    inactive bus consumes only mW. The problem is that some FireWire devices can
    require lots of power (tens of Watts); this would strain the laptop
    somewhat. Some manufacturers seem to have taken the easy option of not
    supplying any power. Personally, I think this is a bit of a crude,
    inconsiderate solution; most laptops could easy provide power for the type
    of device that one would connect to a laptop... and if a particular device
    requires to much power, then the laptop could always refuse to power it
    (either by not turing the device's link on or by current limiting).
    Tim Clacy, Jan 14, 2004
  8. battery power, but no 6-pin firewire. However, you can get PCMCIA
    And PCMCIA FireWire cards often don't provide bus power anyway, as I
    found out to my detriment when I first acquired my iPod. Plus, all the
    PCMCIA FW cards I've seen have a dirty great extension on the end
    holding the FireWire connectors, so they often block your other card
    slot anyway (no XJack devices can coexist with them, for instance).

    Laptop vendors seem to be targeting direct connect to DV camcorders as
    the "killer app" for 1394 on PCs, hence the miniature and unpowered
    connector. FireWire still has a "taste" of Macintosh to PC vendors, I
    think. USB (and USB 2.0, now) are the "PC way".
    Lewin A.R.W. Edwards, Jan 14, 2004
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