Supra said:
Hi all, am I right in thinking 30ft for a USB printer is too long and
it won't work in any case? I bought a 30ft 2.0 cable for a USB printer
and XP fails to recognise it when it's plugged in, I switched to a
short cable and it instantly did. So am I to assume the length of the
cable is the problem, or is the 30ft cable I bought not working
correctly? I seem to recall seeing somewhere that USB cables are
limited to 15ft max for stable performance, that seems stupid
considering parallel cables can go way more than that... and that's
old technology...
Please enlighten...
Thanks,
Julius
Feet is outdated and I can;t quote in it...
but 5M is the specifications limit of USB and USB2 (low speed USB was
3M), at a guess 30ft is about 10M or a bit less, *shrugs* eitherway,
thats definately way too long.
Parallel (IEEE1284) was 10 Meters at 2Mhz, the older ones (SPP) was only
5M, not that much difference.
You can buy Active Extenders (hubs, repeaters) which are powered from the
USB port that can (claimed) link up together to create about a 25M (5
hubs/repeaters max, 5M between them).
This is a manufactures claim, and is not always possible. Just be aware
of this.
Parallel was low speed, and used many lines for the transfer, a VERY
inefficient design, hence why it got dumped, but for the time in
technology, it was way faster then serial, technology has increased in
speed so much the benefit of having several lines is deminished from the
flaws int he systema nd the more eficcient serial system has overtaken it
in terms of data transfer.
The reason 5M is max is due to several reasons.
All serial data is a square wave. now.. electricity flows, and at the
speed of light, but the electrons barely move at all, but (remember this
is crude analogy) ignoring other aspects, just tackle this one for now,
when the wave starts, the power flows, then it goes to 0, and power
stops, this is sudden change takes time.. think of it like at the
traffic lights, go green, front starts moving, slowly stretched out and
then stops atthe next one, compressing, this is very crude, but an
example of how a square wave gets distorted into a sin wave, before after
going too far, becomes constant. this is the capacitance in the wire
smoothning it out, the other technical aspect is the resistance, limiting
it. If its a slow waveform, it will be "high" for longer, and "low" for
longer, giving the receiving end more time to see the data reliably even
tho its being smoothed out. so the faster the data, the more quickly it
loses definition, also being low voltage (5v) the resistance comes into
play very quick. Now, along with all of this, we have the timing issues
involved aswell. Put them all together, and we have a 5M limit.
And as always, theoretical distances are disproven on a daily basis die
to many other factors, cable condition, cable build, temperature,
humidity, the host, the client, so on.
Hope this rough crude analogy explained all your questions.
Cheers.
