3 ms·
what are usb power ports used for? i mean, what devices use them, or is it that devices should use them for some reason?
by diN0bot 17y ago
what are usb power ports used for? i mean, what devices use them, or is it that devices should use them for some reason?
- tb 17y agoMobile phones and digital cameras etc often come with USB cables for charging. The intent is that they be charged from the ports on a computer but there's no reason they can't be charged directly from a socket. The exception is the iPhone, some versions of which will not draw any current from the USB socket until a handshake protocol with the PC is complete, and so they will not charge from this kind of arrangement.
- bedris 17y agoMy BlackBerry is the same way; it will only draw current from the USB socket if it detects the requisite software installed on the computer.
- allenbrunson 17y agomy iPhone came with a little transformer that plugs into the wall for charging. obviously there isn't going to be any handshaking there. i was under the impression that all iPhones were like that. are you saying that some aren't?
- ssharp 17y agoMy iPhone charges from the home adapter that came with the phone, of course. I also have a 3rd party USB charger that I bought two or three years ago for my iPod. It came with both a home adapter and car adapter. The car adapter will charge my iPhone but the home adapter won't.
- rufo 17y agoYour home adapter probably uses the old FireWire power pins, which the iPhone 3G can no longer charge from. There is also a handshake, but that's separate and (as of the 3GS) only displays a "product not designed for iPhone" warning - even if it displays the warning, it still lets you use the device.
- mikepurvis 17y agoI don't believe it's malicious—the "handshake" is just the device requesting that the USB port switch to high-power mode. The line is always 5V, but the device needs to request to draw anything more than 0.1A. In the case of wall-transformers for iPods, phones, etc, they're either using an unstandardized handshake (such as the phone shorting its two data lines, which can be recognized by the transformer with just a relay), or they provide power all the time, which could damage a low-power device that was inadvertently plugged in.