35 foot long usb cable?

[mike]

im a little confused. i read on the usb.com faq (among many other
places) that the maximum length allowed by the usb spec is about 15
feet. but ive seen usb cables longer than that for sale all over the
web. i even found one that was 35 feet long. so whats the deal? why
would any company produce cables that wont work according to the usb spec?

 

[Tomi Holger Engdahl]

mike <no@spam.please> writes:

im a little confused. i read on the usb.com faq (among many other
places) that the maximum length allowed by the usb spec is about 15
feet. but ive seen usb cables longer than that for sale all over the
web. i even found one that was 35 feet long. so whats the deal? why
would any company produce cables that wont work according to the usb
spec?

There are some special long USB cables which are not actually
cables, but more like a combination of active electronics
(USB repeater) and cable. This kind of special cable
can exceed the 15 feet USB cable length limit.


--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

 

[Bob Myers]

"Tomi Holger Engdahl" <then@solarflare.cs.hut.fi> wrote in message
news:lajlluhu5mz.fsf@solarflare.cs.hut.fi...

mike <no@spam.please> writes:

im a little confused. i read on the usb.com faq (among many other
places) that the maximum length allowed by the usb spec is about 15
feet. but ive seen usb cables longer than that for sale all over the
web. i even found one that was 35 feet long. so whats the deal? why
would any company produce cables that wont work according to the usb
spec?

There are some special long USB cables which are not actually
cables, but more like a combination of active electronics
(USB repeater) and cable. This kind of special cable
can exceed the 15 feet USB cable length limit.

It's also possible to go beyond the stated limit of the USB
spec IF the high-speed mode ("high-speed" in this case
being the full 12 Mbit/sec rate of the original USB 1.0 spec,
not the USB 2.0 rates) is never used and the link is restricted
to just the 1.5 Mbit/sec slow rate. But while it would work,
it's not technically compliant with the 1.0 spec, which I believe
required all USB cabling to handle the original max. speed.

Bob M.

 

[Watson A.Name - 'Watt Sun]

In article <3f26d5e4$1@usenet01.boi.hp.com>,
nospamplease@addressinvalid.com mentioned...

"Tomi Holger Engdahl" <then@solarflare.cs.hut.fi> wrote in message
news:lajlluhu5mz.fsf@solarflare.cs.hut.fi...
mike <no@spam.please> writes:

im a little confused. i read on the usb.com faq (among many other
places) that the maximum length allowed by the usb spec is about 15
feet. but ive seen usb cables longer than that for sale all over the
web. i even found one that was 35 feet long. so whats the deal? why
would any company produce cables that wont work according to the usb
spec?

There are some special long USB cables which are not actually
cables, but more like a combination of active electronics
(USB repeater) and cable. This kind of special cable
can exceed the 15 feet USB cable length limit.

It's also possible to go beyond the stated limit of the USB
spec IF the high-speed mode ("high-speed" in this case
being the full 12 Mbit/sec rate of the original USB 1.0 spec,
not the USB 2.0 rates) is never used and the link is restricted
to just the 1.5 Mbit/sec slow rate. But while it would work,
it's not technically compliant with the 1.0 spec, which I believe
required all USB cabling to handle the original max. speed.

And to compound the situation, the USB 2.0 spec was designed to work
with USB 1.0 cables, which means that any cable that doesn't meet 1.0
spec will not work at the 480 MB 2.0 speed, which is 40 times faster
than 1.0.

What irks me is that the stores are pitching these "USB 2.0 cables",
which is as much marketing hype as the "Digital speakers". If the
cables simply meet USB 1.0 specs, they will work at 2.0 speed.

Bob M.

--
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