On Oct 24, 2008, at 10:54 AM, hackmiester / Hunter Fuller wrote:

>
> 2008/10/24 Steve R <[EMAIL PROTECTED]>:
>>
>> At 9:58 AM -0400 10/24/08, Len Gerstel posted:
>>>  So a USB device that is on, whether it is a printer with the power
>>>  switch turned on or a mouse waiting to be moved, will draw power. A
>>>  USB device that is not turned on like a printer or scanner with the
>>>  power switch turned off or power brick unplugged will not draw any
>>>  usb power.
>>
>> Immensely. Thanks.
>
> I have one other correction: Devices like printers don't draw any
> power when on, either - from USB at least. At least on my printer, the
> USB power lines aren't even connected

My thought was about the miniscule amount of power that is used when  
the printer is powered up and is polling the computer over the USB  
lines.

It sends a signal to the computer asking "anything for me to print  
yet? I am still here and powered on."

Maybe the print command is a pure push command from the computer with  
no polling on the part of the printer, so the printer's USB is woken  
up by the signal to print.

But, overall, even when printing, a printer with a power brick will  
use a miniscule, but not zero, amount of power compared to a mouse or  
keyboard.

Len


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