Lots of companies do this. APC puts a RS-232 serial port on a UPS but wait! They move the pins around so you need a special cable. Cisco used to have a product called the Gigastack that used a standard 6-pin Firewire cable, but no! Pins 1&2 were shorted in the "special" cables Cisco provided.
We all love to call out Apple when they design deliberate incompatibility into their devices, but there is a perfectly valid technical reason for what Apple is doing here, and, in fact, they are following a USB specification (which LadyAda unfortunaterly didn't even test).
Without data communications or when suspended, devices may legally draw no more than 2.5mA from a host, which is useless for charging. In fact, even if you're generous and pretend they're connected, devices are not allowed to draw more than 100mA without negotiating for a higher current, which requires actually talking to the host, and 100mA is still too little to charge properly. 500mA is the maximum allowed by the USB spec, but devices must negotiate it (there may be too many devices on the bus for negotiation to succeed).
Before there was a spec for "dumb" USB chargers, Apple used the resistors as a sentinel to avoid drawing too much current from undersized chargers in order to avoid damaging the host. This is a hack, but it works, and honestly, we're smart enough to figure out a couple resistors on the data lines. It's not like they're using crypto auth on the charger. They have a perfectly valid reason to do this. Devices which charge from "dumb" chargers aren't following the spec, though this is a common industry practice.
As it turns out, the USB-IF came up with a USB Battery Charging spec [usb.org]. The spec is long and boring, but it boils down to: short together the data lines (no resistors required) and you indicate that you're a dumb charger that can supply anywhere from 0.5A to 1.5A.
(Yes, I'm not following the USB spec there by in turn using a USB cable to supply the 5V and not negotiating over its data lines. I didn't feel like grabbing a dedicated 5V PSU for the shot, so sue me.)
... so why did they need to impose NDA's on everyone who makes these things? Yes, I understand there's a technical reason to build them this way, but why all the secrecy about it? It's hard to imagine any answer other than "we want to make more profit on cables by limiting competition".
Yep. Owner of iPhone 3 (the older one). Bought a $5 cable to hook it up to composite inputs (TV). Cable works for about 3 seconds, then gives some stupid error message (not exactly "Pay us $45 to make this work" but I interpreted it that way). Fuck Apple. When my contract ends, I'm moving to Android quickly.
As far as I know, the NDA is for devices that talk to their 30-pin accessory connector, including component cables, which do have crypto auth and you need to purchase auth chips from Apple (and yes, Apple deserves all kinds of bashing for that one).
I'm not aware of any NDAs required to make a USB compliant charger; all you need to do is visit the USB-IF website and download the USB charging standard spec, which Apple devices are compatible with. Before the charging spec, they didn't publish the resistor stu
Actually, I just wanted to point out that if you RTFA (instead of just WTFV), you'll see that Lady Ada does in fact acknowledge that the USB spec says some things. Here, I'll quote it for you:
We thought "is there a enumeration chip inside every charger?" but since thats expensive and kind of overkilly we decided instead to read up on the USB protocol (go Jan!) In particular, in her fantastic book there's a part about the low level signaling states. Since you want to get the iPod charging, but NOT make it tr
I did RTFA and WTFV. SE1 (not SEI) isn't the charging signal, it's a USB data line state (an invalid one that goes against the USB spec). A short across the data lines (without connecting them to any explicit voltage) is what indicates a charger according to the USB Battery Charging spec. Now, SE1 could have well been the magic "charger" indication, but it isn't what was chosen for the USB spec.
Apple chargers use the data lines in non-standard ways (pulled to a voltage using resistors), but shorting them to
Older devices probably don't support it (the spec is quite recent after all). At least the iPhone 3G does, and quite likely newer devices too. I don't know about the 2G. Older iPods probably won't work.
As for the current, I measured mine at 500mA in this mode, which is consistent with the minimum requirement for a dedicated charger. I guess the iPhone makes no attempt to draw more unless it detects the specific resistors.
Now, of course, Apple hasn't publicly stated that their devices are compatible with USB
Knowing that other manufacturers may dream up their own way of detecting a wall-wart, I'm guessing non-iPhones are either going to have to figure out a sane data resistance or be SOL for the next MintyBoost.
"A car is just a big purse on wheels."
-- Johanna Reynolds
Not surprising (Score:5, Informative)
Lots of companies do this. APC puts a RS-232 serial port on a UPS but wait! They move the pins around so you need a special cable. Cisco used to have a product called the Gigastack that used a standard 6-pin Firewire cable, but no! Pins 1&2 were shorted in the "special" cables Cisco provided.
Apple is doing the right thing here (Score:5, Informative)
We all love to call out Apple when they design deliberate incompatibility into their devices, but there is a perfectly valid technical reason for what Apple is doing here, and, in fact, they are following a USB specification (which LadyAda unfortunaterly didn't even test).
Without data communications or when suspended, devices may legally draw no more than 2.5mA from a host, which is useless for charging. In fact, even if you're generous and pretend they're connected, devices are not allowed to draw more than 100mA without negotiating for a higher current, which requires actually talking to the host, and 100mA is still too little to charge properly. 500mA is the maximum allowed by the USB spec, but devices must negotiate it (there may be too many devices on the bus for negotiation to succeed).
Before there was a spec for "dumb" USB chargers, Apple used the resistors as a sentinel to avoid drawing too much current from undersized chargers in order to avoid damaging the host. This is a hack, but it works, and honestly, we're smart enough to figure out a couple resistors on the data lines. It's not like they're using crypto auth on the charger. They have a perfectly valid reason to do this. Devices which charge from "dumb" chargers aren't following the spec, though this is a common industry practice.
As it turns out, the USB-IF came up with a USB Battery Charging spec [usb.org]. The spec is long and boring, but it boils down to: short together the data lines (no resistors required) and you indicate that you're a dumb charger that can supply anywhere from 0.5A to 1.5A.
Guess what happens when you short the data lines of an iPhone 3G and supply 5V [marcansoft.com]. Did Apple just follow a standard? Incredible!
(Yes, I'm not following the USB spec there by in turn using a USB cable to supply the 5V and not negotiating over its data lines. I didn't feel like grabbing a dedicated 5V PSU for the shot, so sue me.)
Ok, so I ask the same question as above... (Score:2)
Re: (Score:2)
Re: (Score:2)
As far as I know, the NDA is for devices that talk to their 30-pin accessory connector, including component cables, which do have crypto auth and you need to purchase auth chips from Apple (and yes, Apple deserves all kinds of bashing for that one).
I'm not aware of any NDAs required to make a USB compliant charger; all you need to do is visit the USB-IF website and download the USB charging standard spec, which Apple devices are compatible with. Before the charging spec, they didn't publish the resistor stu
Re: (Score:3, Insightful)
Actually, I just wanted to point out that if you RTFA (instead of just WTFV), you'll see that Lady Ada does in fact acknowledge that the USB spec says some things. Here, I'll quote it for you:
Re: (Score:2)
I did RTFA and WTFV. SE1 (not SEI) isn't the charging signal, it's a USB data line state (an invalid one that goes against the USB spec). A short across the data lines (without connecting them to any explicit voltage) is what indicates a charger according to the USB Battery Charging spec. Now, SE1 could have well been the magic "charger" indication, but it isn't what was chosen for the USB spec.
Apple chargers use the data lines in non-standard ways (pulled to a voltage using resistors), but shorting them to
Re: (Score:2)
Older devices probably don't support it (the spec is quite recent after all). At least the iPhone 3G does, and quite likely newer devices too. I don't know about the 2G. Older iPods probably won't work.
As for the current, I measured mine at 500mA in this mode, which is consistent with the minimum requirement for a dedicated charger. I guess the iPhone makes no attempt to draw more unless it detects the specific resistors.
Now, of course, Apple hasn't publicly stated that their devices are compatible with USB
Re: (Score:1)
Knowing that other manufacturers may dream up their own way of detecting a wall-wart, I'm guessing non-iPhones are either going to have to figure out a sane data resistance or be SOL for the next MintyBoost.