At 8:42 AM +0200 8/3/03, Laurence TeknoLiber wrote: >When I have amy keyboard connected through my >powered 4-port USB hub (iMac kbd short cable), it doesn't >work the way it does if it's plugged directly into the Mac, >e.g. the power key etc. > >Is there an explaination ?
Yes. When the computer is off, small amount of current from the power supply's standby power output is bled into one of the USB lines through a resistor. When the power on key is pressed, this current source is shorted out. A voltage comparator on the mother board senses the corresponding voltage change and signals the power supply to turn on. It is a very elegant hack that allows an otherwise un-powered USB bus to do something it was never designed to do - send a signal when it is off. The hub inserts a USB transceiver between incoming and outgoing USB signals, and this transceiver blocks the signal current. Paul -- G-Books is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Check our web site for refurbished PowerBooks | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> G-Books list info: <http://lowendmac.com/lists/g-books.html> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/g-books%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
