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 iPhone OS on /dev/tty.iap, as a character device. Probably only to jailbroken 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:
This is what mine looks like, I cut the IC's pins a bit and managed to put it all inside the connectors:
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.