ubuntu-phone team mailing list archive

[sturmflut <sturmflut@xxxxxxxxxxxxxx>]

Hi,

in theory data-only cables can be made by removing the 5V VCC
connection. The other three connections are necessary.

In reality the USB specification forbids this:


Section 9.1.1.2

"(..) Although self-powered devices may already be powered before they
are attached to the USB, they are not considered to be in the Powered
state until they are attached to the USB and V_BUS is applied to the
device. (..)"


V_BUS is the VCC connection. Most chip designers use a simple detection
circuit to only activate the slave device port when the host continually
supplies 5V for a given amount of time.

There are some chips on the market which ignore the specification and
work with a data-only cable, but those are rare and usually not found in
smartphones.


Simon



Am 09.04.2015 um 00:07 schrieb Selene Scriven:> * Rodney Dawes
<rodney.dawes@xxxxxxxxxxxxx> wrote:
>> You can probably buy a data-only USB cable for your device, or an
>> adapter which does not include the connections for the 5v power, to
>> install between the cable and your PC.
>
> I tried this; it doesn't work.  A power-only cable works fine,
> but a data-only cable does not.  It behaves as if it's not
> connected at all.
>
> If you'd like to try it, it's easy to do by simply covering the
> VCC pin with tape on the large end of the cable (or both middle
> pins, for a power-only cable).  Kapton tape works great if you
> have some.
>
>
> -- Selene
>