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Why Don't PDAs and Cellphones Use USB?
evolutionaryLawyer asks: "I have a RazrV3 phone and the charging interface is USB. This means if my cell phone is dying I get to pull a USB cable out of my bag, plug it into my laptop and charge it wherever I am, and at the same time data transfer is possible. This got me to thinking, why do all these cellphones, PDAs, and other devices use funky data and power interfaces when USB 2.0 is capable of providing both data and power in a universal format? I cannot think it is to sell cables, because I am sure they lose a lot of that to 3rd parties, not to mention that it has to be more expensive to design and manufacture these proprietary formats. Look at the PSP, it has both a power port, and a USB 2.0 port. Why shouldn't they cut out one?" While such a question is better asked of the cell phone manufacturers, it is unlikely that the average consumer would be able to get a straight answer. Can you think of plausible reasons as to why companies might be bypassing usable standards for their own proprietary cables, especially given the fact that there are third-party cables out there for just about every make and model of PDA or cellphone?
Basic and simple answer, USB adds complexity. If the phone had only a USB plug, it would have to be a USB host to be able to allow things like corded headsets and such to attach. Then the headsets would have to be more complex, going from somethign that just passes analog data over the right pins on the connector to a full digital headset.
Power wise, USB really can't do more then 500mA of power at 5V. This is fine for cell phones like my T610 that get 450mA from the official charger at 4.7V. But for devices like the PSP, it would mean 4 times as long to charge, as the PSP power adaptor pushes out 2A or power at 5V.
It's 500mW max iirc, which is enough to keep most portable devices running, but would make charging really slow.
If they were to go to a standard connection Firewire might be nice at 12-60Wats.
But in the mean time, they'll generally use custom connectors for charging.
"The worst tyrannies were the ones where a governance required its own logic on every embedded node." - Vernor Vinge
From http://www.usb.org/developers/usbfaq/#pow1
1. How much power does a system in S3 need to supply to USB?
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A: 500mA per USB port. See section 7.2.3 for the details of device behavior during suspend and resume.
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Presumably this has something to do with it. HTH. HAND.
I also have a V3, and its USB power can only be used to "top off" an already existing charge. if you ever get the phone to a dead state, a USB port is useless. The usb charging doesnt begin until the software in the phone requests power from the port.
another problem, is that to charge a dead phone you need a motorola(TM) razr(TM) usb charger, which arent very redily available yet.
another problem is that a USB port cant provide enough juice to both charge the phone, and make a call. if you talk on USB power, your phone will eventually go into a totally dead state (see above for how fun that is).
yet another problem, is that file transfer over USB isnt possible (it might be with additional software). I can exchange ringtones and pictures only via bluetooth, and can sync a phone book only with USB. totally wierd.
usb provides the power specification, the cell phone would conform to the USB spec instead of the other way around.
That being said, the RazrV3 has the OPTION of charging off of USB. If the phone is dead it WILL NOT. This is because USB needs a signal negotiation before it will deliver the higher power available on USB 2.0. If the phone is dead, such negotiation is impossible. This is part of the reason that it's not done on more models.
Strangely, my Razr didn't come with a USB cable. It came with a regular wall plug. I don't need the USB (all my computers have bluetooth), but I was kind of surprised by this.
The restrictions on phones over in the US is ridiculous. I got an NEC e616 flipphone in February with all the goodies (dual video cameras, mp3, video calls, 3G network @ 384Kbps) for just under $200 Aust with 3 Mobile. It includes a USB cable and there are no file restrictions on this phone other than content bought through the 3 services (music videos, etc) cannot be copied or moved. And the calendar automatically synchronises over the 3G internet connection with my PC. American mobile carriers are an absolute joke, simple as that.