30 pin connector used on the dock station for iPod and iPhone.
Available in all Apple iPod MP3 player (iPod 1G, 2G, 3G, 4G, 5G and Nano).

iphone接口定義英文版的：

This connector is used on iPod (starting from 3rd generation) and iPhone. It is used to connect the iPod or iPhone to various devices: PC (via USB or FireWire IEEE1394), audio amplifier, serial device (controlled via the Apple Accessory Protocol).

Pin? Signal? Description??
1? GND? Ground (-), internaly connected with Pin 2 on iPod motherboard??
2? GND? Audio and Video ground (-), internaly connected with Pin 2 on iPod motherboard??
3? Right? Line Out - R (+) (Audio output, right channel)??
4? Left? Line Out - L(+) (Audio output, left channel)??
5? Right In? Line In - R (+)??
6? Left In? Line In - L (+)??
8? Video Out? Composite video output (only when the slideshow mode is active on iPod Photo)??
9? S-Video Chrominance output? for iPod Color, Photo only??
10? S-Video Luminance output? for iPod Color, Photo only??
11? GND? Serial GND??
12? Tx? ipod sending line, Serial TxD??
13? Rx? ipod receiving line, Serial RxD??
14? NC??
15? GND? Ground (-), internaly connected with pin 16 on iPod motherboard??
16? GND? USB GND (-), internaly connected with pin 15 on iPod motherboard??
17? NC??
18? 3.3V? 3.3V Power (+)
Stepped up to provide +5 VDC to USB on iPod Camera Connector.
If iPod is put to sleep while Camera Connector is present, +5 VDC at this pin slowly drains back to 0 VDC.??
19,20? +12V? Firewire Power 12 VDC (+)??
21? Accessory Indicator/Serial enable? Different resistances indicate accessory type:

1KOhm - iPod docking station, beeps when connected

10KOhm - Takes some iPods into photo import mode

500KOhm - related to serial communication / used to enable serial communications Used in Dension Ice Link Plus car interface

1MOhm - Belkin auto adaptor, iPod shuts down automatically when power disconnected Connecting pin 21 to ground with a 1MOhm resistor does stop the ipod when power (i.e. Firewire-12V) is cut. Looks to be that when this pin is grounded it closes a switch so that on loss of power the Ipod shuts off. Dock has the same Resistor.

22? TPA (-)? FireWire Data TPA (-)??
23? 5 VDC (+)? USB Power 5 VDC (+)??
24? TPA (+)? FireWire Data TPA (+)??
25? Data (-)? USB Data (-)??
26? TPB (-)? FireWire Data TPB (-)??
27? Data (+)? USB Data (+)
Pins 25 and 27 may be used in different manner. To force the iPod 5G to charge in any case, when 'USB Power 5 VDC' (pin 23) is fed, 25 must be connected to 5V through a 10KOhm resistor, and 27 must be connected to the Ground (for example: pin 1) with a 10KOhm resistor.??
28? TPB (+)? FireWire Data TPB (+)??
29,30? GND? FireWire Ground (-)??

Notes
Signals with grey background may not exist on some docking stations.
Apple serial devices (i.e. iTalk and remote control) communicate with iPod (3rd generation or more) using the Apple Accessory Protocol.
The serial connection uses a standard 19200 baud 8N1 protocol (the speed can be increased up to 57600 but tends to become unstable).

來個中文的iphone接口定義：

接口排列方式為:
1.2.3.4.5.6.7.8.9...........29.30

內部焊接點排列為:

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

接口定義為:
1 Ground (-) 地 *
2 Line Out - Common Ground (-) 線路輸出 地*
3 Line Out - R (+) R聲道線路輸出
4 Line Out - L (+)L聲道線路輸出
5 Line In - R (+) R聲道線路輸入
6 Line In - L (+) L聲道線路輸入
7
8 Video Out - Composite Video (for ipod colour when slideshow activated) 復合視頻輸出 (只有彩屏的ipod有效)******
9
10
11 Serial GNDRS-232串口 地
12 Serial TxD RS-232串口 TxD
13 Serial RxD RS-232串口 RxD
14
15 Ground (-) 地 **
16 USB GND (-) USB電源負極 **
17
18 3.3V Power (+) 3.3V電源正極
19 Firewire Power 12 VDC (+) 1394火線12V電源 正極 ***
20 Firewire Power 12 VDC (+)1394火線12V電源 正極***
21 Accessory Indicator 附件識別接口 ****
22 FireWire Data TPA (-) 1394火線數據 TPA(-)
23 USB Power 5 VDC (+)USB 5V 電源 正極
24 FireWire Data TPA (+) 1394火線數據 TPA(+)
25 USB Data (-)USB 數據(-)
26 FireWire Data TPB (-)1394火線數據 TPA(-)
27 USB Data (+) USB 數據(+)
28 FireWire Data TPB (+) 1394火線數據 TPB(+)
29 FireWire Ground (-) 1394火線12V電源 負極*****
30 FireWire Ground (-) 1394火線12V電源 負極*****