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General discussion

When is USB 2 not USB 2?

by jason_mackinlay Feb 15, 2009 11:03AM PST

I am trying to setup some USB hubs on a wireless network and having some trouble with USB versions.

I have discovered that a USB hub which was analysed by a diagnostic as USB 2.0 was connected to a USB 1.1 root hub on my laptop at a speed of 12Mbps. All devices connected through it also connected at 12Mbps with the expected 'this device can perform faster' info message from Windows. The same devices (a few memory sticks, external HDD and a printer/scanner) all connected at high speed USB 2.0 when directly plugged into the same USB port.

So how can a USB 2.0 device, in this case the hub, be connected as USB 1.1?

Thanks,

Jason

Discussion is locked

6 Posts
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powered?
by mementh Feb 15, 2009 4:23PM PST

is it a powered hub? it might be limited due to the power not being plugged in if thats the case?

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Just BUS powered
by jason_mackinlay Feb 16, 2009 11:30PM PST

The hub only transfers power from the laptop and doesn't have its own power supply. It works successfully with memory sticks and an optical mouse, but then won't recharge my phone.

The external hard disk has it's own power supply but won't connect through it at all.

I've started looking at powered hubs now but that's going to be annoying for travel.

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USB has a current draw limit per powered port
by fbbbb Feb 23, 2009 8:18PM PST

A powered port - i.e. a USB port that is working directly off a powered device, so a port on a powered USB hub, off a computer, etc - has a limit on the amount of power it can provide. The limit is 500ma at 5V.

Unpowered hubs therefore draw 500ma at 5V minus the current they need to power the hub itself, and often can't power anything which has a high single (HDD's, iPods, Phone recharging, etc), or high combined current draw (multiple lower-demand devices).

Most HDD's for example demand the full power that a single powered USB port can supply. So if you suppose that the hub itself needs 50ma to work, that from 500ma is 450ma - leaving the hard disk short.

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But why connect as USB 1.1?
by jason_mackinlay Feb 23, 2009 10:57PM PST

Well that could explain why the HDD / others couldn't connect through it, but why is the hub connecting as USB 1.1 (12Mbps transfer) even before any devices are attached?

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That could be a hub issue.
by fbbbb Feb 24, 2009 2:07AM PST

You didn't have it hanging off another hub, did you (like one on your keyboard)?

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Not a daisy chain of hubs
by jason_mackinlay Feb 24, 2009 5:42AM PST

No, it's the only hub attached to the laptop, and the HDD and memory stick both connect at 480Mbps when directly connected to the same USB port.

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