power on firewire port ?

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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
http://www.alciom.com




Re: power on firewire port ?
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Section 4.2.2.7 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                        mailto: snipped-for-privacy@oxsemi.com
Oxford Semiconductor Ltd          http://www.oxsemi.com
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Re: power on firewire port ?
MANY THANKS !

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

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(shared
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Re: power on firewire port ?
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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:

1394 TRADE ASSOCIATION
Power Specification
Part 1: Cable Power Distribution
Doc1999001_Part1.pdf

1394 TRADE ASSOCIATION
Power Specification
Part 2: Suspend/Resume Implementation Guidelines
Doc1999001_Part2.pdf

TA Document 1999001-3
Power Specification
Part 3: Power Distribution Management
Doc1999001_Part3.pdf




Re: power on firewire port ?
snipped-for-privacy@nospamphaseone.nospamdk says...
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Correct.


Apart from the aforementioned laptops.

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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                
2reply remove FOOBAR
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Re: power on firewire port ?

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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 ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: power on firewire port ?
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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).

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Re: power on firewire port ?
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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".

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