On 5/13/10 1:34 PM, Bruce Johnson wrote:
On May 13, 2010, at 12:32 PM, Kris Tilford wrote:
What could have changed?
The battery is lower on charge, and is drawing more amperage than
before. The limit is 500mA total per USB port unless you have an
external USB hub with its own power supply. I've seen this message
before using a USB memory stick to a keyboard port. Since the USB
memory stick doesn't draw significant power, this might be an error
specific to keyboard ports that you can safely ignore, at least
that's what I did.
Also the Mac keyboard ports are lower power than normal, because
they're an unpowered hub. I've seen some older USB flash drives
produce that warning.
There is a maximum of 500mA available from a powered port (on the
computer or a powered hub). Each device is allocated a minimum of
100mA. The hub inside the keyboard, the keyboard itself, the mouse and
the camera are likely each requesting the minimum of 100mA so that's a
total of 400 mA allocated. That leaves 100mA still available so this
problem SHOULDN'T be happening. If the keyboard is plugged into an
unpowered hub you could get this problem.
USB is in many ways a well thought out specifications but the
implementation frequently falls short.
I have seen some USB devices that request 500mA regardless of what they
need. I suspect the programmers were just being lazy.
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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