Enhanced mini-USB

An EMU connector, or enhanced mini-USB, is a type of hybrid electrical connector, which carries both Universal Serial Bus data and power, as well as other additional connections, usually bidirectional audio. It was invented for and is mainly used on mobile phones. Motorola appears to be the primary manufacturer of mobile phones using EMU connectors, although the HTC TyTN and others use it as well. [http://www.tracyandmatt.co.uk/blogs/index.php/2006/09/10/htc_hermes_usb_connector_pin_config] There is more than one standard for EMU connectors, which are incompatible between manufacturers, but always still compatible with regular mini-USB.

Physically and electrically compatible with standard mini-USB connectors, the EMU connector has the five pins for USB on one side. But rather than being empty on the other side, it typically has more pins intended for headsets. In HTC's version, two pins are for the microphone, three are for stereo sound (for two-ear headphones), and one is for the push-to-talk switch. (It is presumed that one of the microphone conductors must be the other side of the switch circuit.)

In the CEA-936-A standard, there are no extra pins — the USB data pins are also used for RS-232 transmit and receive, stereo audio left and right, or for microphone and speaker/earpiece. Auto-detection usually makes this plug-and-play, or it may depend on user settings or the context or mode in which the device is being operated. Two different functions cannot be used at once.

Inconveniently for the consumer, using the connector may require a breakout cable or special headset, keeping proprietary what would otherwise be relatively open standards. Most often, the user must buy a special dongle or pigtail to make the correct connections to a 2.5mm TRS connector for a monophonic headset or 3.5mm for stereo headphones, a form of vendor lock-in. True breakout cables which provide all connections appear to be unavailable, thus a phone cannot be charged at the same time as a headset or headphones are inserted, even for EMUs with extra pins.

Additionally, the extra pins may provide for a more draconian form of vendor lockdown. Because mini-USB provides an extra pin "X", some mobile phone companies have abused this in order to enforce the use of their own battery chargers, sold at inflated prices with very high profit margins. Currently, Verizon Wireless is the only company to cripple phones in this manner, colluding with Motorola to put an arbitrary 1.4 volts on pin X, with no other purpose than as an anti-competitive practice. This voltage violates the USB-IF standards, as pin X should either be tied to ground or not connected at all. Without this connection, the phone will refuse to charge, displaying "unathorized charger" despite having the correct five volts (regulated) that USB inherently provides, thus defeating the purpose of having an otherwise universal USB-based connector in the first place. (The phone will charge from a personal computer, but only if it is running a special device driver, something which almost no other USB devices now need. This means Windows XP must be running, and the phone will again refuse to charge as soon as sleep mode begins even though full power is still being supplied by the computer or USB hub.)

The EMU connector may not last long, as U.S. manufacturers have agreed on micro-USB connectors as an industry-wide standard.

ee also

* Sync cable

External links

* [http://www.tracyandmatt.co.uk/blogs/index.php/2006/09/10/htc_hermes_usb_connector_pin_config HTC data]
* [http://wiki.openezx.org/EMU Motorola data]