> You need a driver on the PC so that the Blackberry can be put in a  
> valid USB configuration to get 500mA.
and
> you need to do certain things to allow charging from the USB port.

You guys are missing the point.  There is no actual USB host port  
involved here, and the cheap dumb USB charger surely does not contain  
a "driver" that allows the blackberry to "request" to be charged.

What does seem to happen is that the Data lines of the USB port get  
pulled up or down by some chargers, and the matching devices use the  
direction and/or detected value of the resistors to sense that they  
are connected to a "legitimate" charger.  In order to get your  
"alternative device" to function as a charger, you have to match (more  
or less) the pullup configuration.  (It might ALSO work to instantiate  
the device as a full USB peripheral on a real USB host port.  Or not.   
I think I've plugged in some devices to real USB ports only to get  
messages about "this device can not be charged on this port."  Grr.)

There is some discussion here http://www.ladyada.net/make/mintyboost/faq.html
(and related pages.)

BillW

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