Re: Stop swimming upstream
From: Michael Unger (unger_at_decus.de)
Date: 08/30/03
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Date: Sat, 30 Aug 2003 17:40:37 +0200
On 30-Aug-2003 16:27, Larry Kilgallen wrote:
> In article <biq5qb$c4p5b$1@ID-152801.news.uni-berlin.de>, Michael Unger <unger@decus.de> writes:
>
>> Does the LK463 keyboard come with an integrated USB hub? It would be
>> convenient to connect the mouse to the keyboard instead of directly to
>> the system if the keyboard is located away (within the USB limitations)
>> from the system.
>
> Isn't the whole reason for a USB hub that one needs more power ?
Not neccessarily.
>
> Having an extra power cord to the keyboard would defeat the goal
> of reducing complexity.
Indeed.
>
> A daisy-chain connector like the ADB keyboard on which I am typing
> this would be nice, but I am under the impression that is contrary
> to the electrical design of USB.
There are two types of hubs: *active* hubs (with an extra power supply)
and *passive* hubs. There are two types of devices: *low* power devices
(consuming less than 100mA) and *high* power devices (consuming more
than 100mA but less than 500 mA). Keyboards and mice are low power
devices of course.
A USB port of a computer is specified to *deliver* up to 500mA of
current to devices. This can be "splitted" into 100mA for a passive hub
and 4x 100mA for low power devices; devices have to start up in low
power mode and "query" the bus whether more power is available.
And there are devices consuming large amounts of power but still acting
as low power USB devices (printers, PBX systems, ...) because they have
an internal power supply.
Please see <URL: http://www.usb.org/developers/docs> for details. (No,
I'm no USB developer ... ;-)
Michael
-- Real names enhance the probability of getting real answers. Please do *not* send "Security Patch Notifications" or "Security Updates"; this system isn't running a Micro$oft operating system. And don't annoy me <mailto:postmaster@[127.0.0.1]> please ;-)
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