| Mobile phone interface pin | Siemens x55 and other old | Siemens x65, x75, SX1 | Description |
|---|---|---|---|
| 1 | Vin | Power Charging | Vbus in in SX1, SL65, SF65 and others x65, x75 |
| 2 | Gnd | GND | usb GND in x65, x75, SX1 USB cable |
| 3 | Tx | TX / USB D+ | usb D+ in x65, x75, SX1 |
| 4 | Rx | RX / USB D- | usb D- in x65, x75, SX1 |
| 5 | CTS | CTS | Data Line For Accessory. Used as a cable detect in Siemens x65-x75 models. Short to pin 2 GND to force cable detection. |
| 6 | RTS | RTS | Data Line For Accessory or serial cable |
| 7 | DCD | DCD | Clockline For Accessory |
| 8 | Audio P | AUDIO L | |
| 9 | - | AUDIO GND | |
| 10 | Audio N | AUDIO R | |
| 11 | GND Mic | GND (EXT MIC.) | |
| 12 | EPP | EPP 1 (EXT MIC.) |
Pins 5,6,7 should be shorted by 10KOhm resistors to pin 2 in x65, SX1 USB cable.

