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Multiple contacts on Apple connectors





weableandbob
There's something that's been puzzling me for a while now. If you look at an Apple iPod/iPhone cable, there are 6 visible and distinct contacts. Yet, it is a USB connection, which (for at least 2.0; Don't know much about 3.0) only has 4 wires. What's the point of having two extra contacts?
william
Hang on, what cable are you looking at? As far as I recall, the Apple Dock connector has 30 pins. which consist of not just USB pins, but also firewire pins, video pins, line-in and line-out pins, Tx/Rx pins, respective ground pins, etc. I'm not entirely sure what Apple cable only has six pins.
weableandbob
I'm looking at the cable that came with my iPod classic a few years ago. It has 30 little slots on the end that connects to the iPod, but only 6 of them appear to have any sort of contacts in them. What's confusing me is why there would be 6 instead of 4 since USB only uses 4 wires, and therefore would only need 4 contacts.
Mr_Howl
I think some of them are to identify the device and authenticate it. So, for example, the iPod knows that it's a USB cable and not one of those Volume/Track/Pause control pad things (Although on the iPod Classic I think there's another slot for that thing...). Or an FM transmitter, a keyboard, etc.

And have you ever plugged your iPod into, say, an FM Transmitter, and got that message "Charging is not supported with this accessory"? I have a feeling Apple charges accessory companies to have their Vendor ID recognized by the device, so that their charger will be supported by the iPod. The cheaper ones probably just fake it, or clone a bigger company's ID.

But maybe not. It could just be identifying the nature and capabilities of the accessory.

That's my theory anyway.
william
^ I think you may be on to something. I do know that the pinouts of the dock connector have constantly changed, and the internal circuitry makes the whole setup less than straightforward (making it harder for clones).

However, is it possible that the two extra pins on the USB connector are simply for audio? At least, that's what I can infer from this. I'm not sure if that dock connector is the same thing as the USB cable, but who knows what Apple has in mind. Apparently the older iPod Touch, the Shuffles, and the Classics all have slightly different pin layouts. Confused

But then again, with only four pins on the USB side, I don't see where the audio would be going. Unless it's like the old Shuffles, which transferred audio on the USB data pins. Maybe the circuitry is designed to do the same thing here, but with separate pins initially.
weableandbob
I suppose it's also possible that it's just meant to work with multiple Apple devices. I haven't checked myself, but it's possible that other iPods/iPhones released at the same time as mine had pins in different locations on the device itself, and adding more pins on the cable just made sure that it was usable with devices other than the iPod classic. Or perhaps Apple just did it to mess with people who are curious about this kind of thing Razz
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