The SD4001 has one DB9 serial port which can selected to be an RS232, RS485 or RS422 port.
By default the SD4001 is configured in RS232 mode.
Electrical RS-232/422/485 selection can be made via software UI (no jumpers). Alternately can override software selection by earthing pin 9 on DB9.
RS-422 uses a full duplex transmit on TX+ (ransmit Data +) / TX- (Transmit Data -) pair, receive on RX+ (Receive Data +) /R X- (Receive Data –) pair.
RS-485 uses half duplex over single pair. For RS-485 which is a 2-wire bus that drives D+ and D- from a native 4-wire interface you need to loop 3-6 and 2-7 on the DB-9.
Note: The earlier Rev 0 model of the SD4001 had a jumper block as shown below. It shipped by default in RS232 mode,with a vertical jumper in place on the left hand SEL pins. To set the port in RS422 or RS485 mode you must remove the SEL jumper and then configure the Signaling Protocol using the Mgt UI. This model is Eol (http://opengear.com/images/EoL%20May18%202012.pdf)
The DB9 pin-out for the Rev 0 model was:
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