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The NB3710 has an M12 extension connector with 8 pins. The 8 pins are split into two logical ports: Pin 1 to 4 form extension port 1 (EP1) and pin 5-8 form extension port 2 (EP2). If possible, EP1 always host the serial line of the router, which is a 3-wire RS-232.
There exist some NB3700 special variants that use the Digital I/O connector as extension ports. The same pin assignment applies for these variants.
| Pin | Port | NB3710 Base | with CAN Option | with IBIS Option | with RS485 Option | with 2nd RS-232 Option |
|---|---|---|---|---|---|---|
| 1 | EP1 | 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 |
| 3 | EP1 | RS-232 RxD | RS-232 RxD | RS-232 RxD | RS-232 RxD | RS-232 RxD |
| 4 | EP1 | - | - | - | - | - |
| 5 | EP2 | - | GND | Call GND (Aufrufbus) | RS485 GND | 2nd RS-232 GND |
| 6 | EP2 | - | L | Call Signal | RS485 TxD-/RxD- (A) | 2nd RS-232 TxD |
| 7 | EP2 | - | H | Reply GND (Antwortbus) | RS485 TxD+/RxD+ (B) | 2nd RS-232 RxD |
| 8 | EP2 | - | - | Reply Signal | - | - |