====== NB3710 Extension Port ======
The NB3710 has an M12 extension connector with 8 pins. The 8 pins are split into two logical ports: pins 1 to 4 represent Extension Port 1 (EP1) and pins 5 to 8 represent Extension Port 2 (EP2). In common, EP1 hosts the serial conslole of the router which corresponds to a 3-wire RS-232.

Some NB3700 variants use the Digital I/O connector as extension connector. The same pin assignment applies for these variants.
===== NB3710 Extension Connector PIN Assignment =====
^Pin^Port^Base^Audio (A)^CAN (C)^IBIS (I)^RS-485 (Sa)^RS-232 (S)^
| 1 | EP1 | RS-232 GND | RS-232 GND | RS-232 GND | RS-232 GND | RS-232 GND | RS-232 GND |
| 2 | EP1 | RS-232 TxD | RS-232 TxD | RS-232 TxD | RS-232 TxD | RS-232 TxD | RS-232 TxD |
| 3 | EP1 | RS-232 RxD | RS-232 RxD | RS-232 RxD | RS-232 RxD | RS-232 RxD | RS-232 RxD |
| 4 | EP1 | - | - | - | - | - | - |
| 5 | EP2 | - | Input Left Ch. +     | GND | WBSD (Signal Call/Aufrufbus) | RS485 GND | 2nd RS-232 GND | 
| 6 | EP2 | - | Input Left Ch. -      | L | WBMS (GND Call/Aufrufbus)  | RS485 TxD-/RxD- (A) | 2nd RS-232 TxD |
| 7 | EP2 | - | Output Left Ch. +  | H | WBED (Signal Reply/Antwortbus) | RS485 TxD+/RxD+ (B) | 2nd RS-232 RxD | 
| 8 | EP2 | - | Output Left Ch. -   | - | WBME (GND Reply/Antwortbus) | - | - | 
===== M12 Extension Connector =====
{{:pictures:m12-dio.png?nolink&200|M12 Extension Connector}}