Re: Is a USB cable for data, or only power; how to tell without testing it?

In article <[email protected]>, Mark Lloyd
<[email protected]> wrote:

> [snip]
> 
> > there is no such thing as a usb power-only cable because it's in
> > violation of the spec. the amount of current must be negotiated over
> > the data lines, so a 'power-only' cable' that has no data lines will be
> > unable to negotiate and end up at the default 100ma.
> 
> They exist.

what exists are not compliant with the usb spec which means they are
not usb cables.

such cables might work if the devices are also non-compliant, but there
could be all sorts of problems in using such a cable and/or the device.

compliant devices *require* data lines since that's how power is
negotiated. without data lines, 100ma is the maximum, which is not
enough to charge a modern device. if the charger is sourcing higher
currents without proper negotiation, then bad things can happen.

> I used to have a phone that wouldn't charge over a regular 
> cable, but required the power-only one. I no longer have this phone, and 
> don't remember the charge rate.

then at least one part was non-compliant.

it's possible you had three non-compliant components (phone, cable,
charger) and got lucky.