| Pin | Pin Name |
Description |
| 1 | POWER | I/O for charging the battery and for supplying external accessories by reducing standby-time |
| 2 | GROUND | Digital Ground |
| 3 | TX / D+ | Out for Serial-Interface, I/O for USB-Interface full-speed 12Mbis/s |
| 4 | RX / D- | In for Serial-Interface, USB-Interface full-speed 12Mbis/s |
| 5 | DATA / CTS | I/O Data-Line for accessory-bus, use as CTS in data-operation |
| 6 | RTS | I/O use as RTS in data-operation |
| 7 | CLK / DCD | I/O Clock-Line for accessory-bus, use as DTC in data-operation |
| 8 | STEREO1_OUT | Analog Out, driving ext. left speaker to Pin 9 with mono-headset. Pin 8 and Pin 10 differential mode |
| 9 | PHANTOM_BUF_OUT | Analog Out, mid voltage, in stereo-mode reference to Pin 8 and Pin 10, in Mono-mode not used |
| 10 | STEREO2_OUT | Analog Out, driving ext. right speaker to Pin 9 with mono-headset. Pin 8 and Pin 10 differential mod |
| 11 | GND_MIC | Analog In, for external microphone |
| 12 | MICEA_AC | Analog In, external Microphone |
Source: Original Siemens sm_CX75_M75_L2.5e_R1.0.pdf
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