[filmscanners] Re: high speed USB vs low speed

["Mats Petersson" <mats.petersson@btconnect.com>]

At 03:43 PM 1/15/2003, you wrote:
>Mats, thanks for the info.
>
> >  I beleive the HP product is using the "high speed" of the 1.x standard.
>This would be 12 Mb/s.
>
>My mother board was recently(six months ago) installed.  It is a P4 Titan
>533:  6 USB 1.1 Ports
>(2 x Rear, 4 x Front by cable)
>
>How do I determine whether it is the 12 Mb/s USB or the slower 1.5 Mb/s USB?
>Thanks for the help.    Dale

Sorry for not being clear. Short answer: It will do 12Mb/s if the scanner
wants that speed (most likely!).

Longer answer:
All USB 1.x ports should be capable of 12Mb/s, but are ALSO able to do
1.5Mb/s if the device it's connected to doesn't request the higher speed.
Again, USB 2.0 covers ALL the speeds down to 1.5Mb/s, and would of course
start talking slowly, and then up the rate according to what the device
requests.

So basicly it works like this: when you plug in the device (or power up the
system and the system starts scanning USB ports), there is some standard
protocol that is run at 1.5Mb/s, and in this is information for the OS to
determine what type of device it is (scanner, mouse, keyboard, hard disk,
Flash media, Digital Camera, etc), who produced it etc, but also what speed
the device wants to run at. If it's a high speed device (12Mb/s or 480
Mb/s), the future communication will shift to this speed. However, if it
was a mouse that was plugged in, the mouse will say "I only want 1.5Mb/s"
and stay at "slow" speed...

[This is how I understand the workings of USB, I could have some details of
it wrong, but I'm pretty sure it's correct from a functional perspective,
even if some details may be different in the exact method it works.]

Does this make sense to you?

--
Mats



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