Quote:
Originally Posted by induna
It is my understanding that there are two protocols for charging the reader (and other USB devices) -- one for when it is connected to a computer with the data lines active and the other when it is connected to charger with no data connection. If the charger is wired improperly to use the computer connected protocol, it will not work with the reader (or many other USB devices).
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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.