Quote:
Originally Posted by mwheinz
Hoss, I've been a computer engineer for 25 years now. There is no "charging protocol" in USB - at least there is no need for one. Any "protocol" layered on top of simply providing the power levels specified in the USB standards is, by definition, a proprietary hack to keep 3rd party devices from working correctly.
For example, check out this picture. One pin provides +5v, another provides Ground. Current is limited by the spec to 500ma (although it is common for computers to provide more than 500ma for devices that draw a lot of power, like HDs). There is no need for the data pins to get involved when transferring power. |
OK so protocol was the wrong word, Hoss.
However if the data pins are being used by the charger the reader will think it is connected to a computer and will not charge properly. That's why users report seeing the 'Connected to Computer' message on their screen when connected to charger that will not work. A charger that only addresses +5v and GND pins will charge the reader fine (I don't know if the data pins are simply left open or if the need to be shorted together). When that type of charger is connected to one of the new readers, the charge light comes on but the the 'Connected to Computer' message does not display and the reader is still usable while charging.
Many third-party USB chargers work fine with the readers. Some do not.