5 May
2012
5 May
'12
10:52 a.m.
On 05/05/2012 17:39, Alexander Schreiber wrote:
Actually there is sometimes a good reason. For example, an iPhone can
pull far more current than USB guarantees (well over an amp), so it
tests first. The proper charger has a couple of voltage dividers across
the power such that the data +/- lines are held at specific voltages
even at light load. If the voltage on each is within a specific (fairly
narrow) range the iPhone knows it can pull at least an amp. A different
range tells it 500mA. Else nothing.
See, for example,
http://www.engadget.com/2010/08/04/hacker-reveals-how-apple-artifically-res…
Otherwise, I agree, if a lower-power device only needs what it can get
On Sat, May 05, 2012 at 11:56:35AM -0400, Mouse wrote:
The connector
is not all there is to it. I recently ran into a device
(not a phone, but it wouldn't surprise me if phones did the same thing)
that, if you plug in the wrong charger, even though the connector is
correct, displays a snarky message about how you have to use the
charger and cable that came with the device, and refuses to charge.
That is someone playing silly games. If you remember, name & shame
please from a normal USB port, there is absolutely no reason
for it to be
picky, and shame on any designer or manufacturer who plays stupid
games
around device detection. Why Apple stuff sometimes won't work with an
otherwise perfectly good USB cable is beyond me (and deplorable).
--
Pete Peter Turnbull
Network Manager
University of York