Apple’s 30-pin Dock Connector

When Apple introduced the third generation iPod in April 2002, it added a new 30-pin dock connector that could charge the iPod from FireWire, as with all prior iPods, and USB, which finally came to the iPod with the 3G model. While the plug and port were unchanged, over time some pin assignments changed.

Apple 30-pin dock connector

For USB, you only need four pins. For FireWire, six to support data and charging. So why does the dock connector have 30 pins?

It has so many pins because Apple didn’t know how many it might need. Between USB and FireWire, you need 10 (you can’t use the same ground for 12V FireWire and 3.3V or 5V USB). If you want stereo audio output, add 3 more (right, left, and ground). Audio input? Same thing. Video out? With composite and S-video, you need 4 including ground.

That’s got us up to 20 pins. Over time, Apple ended up using 27 of 30 pins, leaving two as reserved and one as unknown.

Pre-2008 devices with the dock connector can charge using the FireWire pin; devices introduced in 2008 and later cannot charge from the FireWire pin. This is the reason some older devices with iPod dock don’t charge more recent devices.

Dock Connector Pin Assignments

This listing follows Apple’s numbering convention, which is the opposite of that used by most sites. This information has been distilled from several websites linked below.

  1. FireWire ground
  2. FireWire ground
  3. FireWire data TPB +
  4. USB data + *
  5. FireWire data TPB –
  6. USB data – *
  7. FireWire data TPA +
  8. USB power +5V
  9. FireWire data TPA –
  10. Accessory indicator/serial enable **
  11. FireWire power 12V+
  12. FireWire power 12V +
  13. 3.3V power
  14. reserved
  15. Ground
  16. Ground
  17. reserved
  18. iPod receive, serial Rx
  19. iPod send, serial Tx
  20. Audio_SW, sends sound to device speaker unless grounded
  21. S-video luminance – iPod photo and iPod color only
  22. S-video chrominance – iPod photo and iPod color only
  23. Composite video out – only used when iPod photo is in slideshow mode
  24. unknown
  25. Left audio in
  26. Right audio in
  27. Left audio out
  28. Right audio out
  29. Audio ground
  30. Ground

* Pins 4 and 6 may be used in a different manner.

** Resistance indicates type of accessory:

  • 1kΩ = docking station
  • 10kΩ sets photo import mode on some iPods
  • 6.8kΩ = serial port mode
  • 68kΩ
    • send audio through line-out (iPod touch, iPhone 3G)
    • disable audio redirection (iPod nano 5G)
  • 500kΩ = enable serial communication with Dension Ice Link Plus
  • 1MΩ = Belkin auto adapter, shuts down iPod when power is disconnected

Resources

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