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iPhone Serial Port

iPhones and iPods have a serial port on the dock connector, used to communicate with accessories at 3.3V levels and with no flow control. Using a MAX3232 and some capacitors, you can convert the signals to RS-232 levels used by most hardware.

Software

The serial port is accessible to software under iOS on /dev/tty.iap (not to sandboxed apps).

Dock Connector to RS232

To build an adapter, the following components are needed:

  • iPod Dock Connector (male)
  • DE-9 Connector (male)
  • MAX3232 IC
  • Five 0.1µF capacitors

We'll use these pins on the dock connector :

Pin Signal Description
1 GND Ground
12 TxD Transmit data
13 RxD Receive data
18 3.3V 3.3V power

And here is the schematic for the adapter:
View PDF

This is what mine looks like, I cut the IC's pins a bit and managed to put it all inside the connectors:
ipodrs232-a.jpgipodrs232-b.jpg

RS232 to Macintosh

To connect to a Macintosh or Newton with a MiniDIN 8 serial, you'll also need the following cable:

MiniDIN 8 Pin Mac Signal RS232 Signal DE-9 Pin
1 HSKo CTS 8
2 HSKi RTS 7
3 TxD- RxD 2
4 GND GND 5
5 RxD- TxD 3
7 GPi DTR 4
8 RxD+ GND 5

If you're just going to use it for an iPhone, you only need the connections on pins 2, 3 and 5 of the DE-9 connector, since the others are used for hardware flow control, and aren't connected on the iPhone side.

References