Originally Posted by goboatingnow
Care to elaborate , I've not seen it called that , what you may be saying is that a device requiring more then 100mA is supposed to negotiate a USB handshake. However the trend in all apple devices is to take as much as the charger provides
Or are you talking about the 2.75V needed on the D+/D- pins ? , this is how apple detects the charger attached. ( easily spoofed up with a few resistors by the way )
Yes spot on ( although it is in 100MA steps up to 500mA. So you will generally get 500mA out of a simple socket wired with 5v on the power pins).
The voltages on the data pins are different depending on the power that the the USB socket can provide.
Thus the voltage tells the iPad
it can draw. 0.5,1.0, or 2.1A.
Without these voltages the iPad
will only draw 500mA which won't charge the battery
Apple have not officially released the voltages, but they are easy found on the web. Using a couple of resistors to the data pins suitable voltages can be generated and the device will charge at the full 2.1A.
A USB socket wired like this will work fine with non apple products.
I believe Samsung do the same thing (and fortunately use the same voltages) with some of their tablets.