Hardware Setting & Mode Configuration

Outside the unit, there are four 4-pin DIP switches which are set to select the mode of operation. You will need to set the switch settings to RS-422 mode, or RS-485 mode, as per the requirements of your application.After setting of switches and connecting power supply to the adapter, you then plug the adapter to USB port to start driver installation. The RS-422 & RS-485 Mode Block Configuration Settings are listed as follows.

 

RS-422 & RS-485 Mode Block Configuration

 

SW1 (PORT1), SW2 (PORT2), SW3 (PORT3), SW4 (PORT4)
 

Operation Mode

S1

S2

S3 S4
RS-422 4 wire with handshaking

ON

ON


OFF

OFF
RS-485 Full Duplex (4 wire)

ON


OFF


OFF

OFF
Half Duplex (2 wire) - with Echo


OFF


OFF


OFF

ON

Note

Half Duplex (2 wire ) - without Echo


OFF


OFF

ON

ON

Note

 

Note : In the most common situation , a 120 Ohm termination resistor of TxD (S4 is ON ) is required in a RS485 Half Duplex configuration. Otherwise it is rarely used.

Inside the unit, there are four 6x2 (8pin) header blocks which are jumpered to enable Rx, CTS 120 Ohm termination resistors and Rx, Tx 750 Ohm biasing resistor. You will need to open up the case and set the jumper setting for RS-422 mode or RS-485 mode as per the requirements of your application. Settings are listed as follows.

 

JP5(PORT1), JP6(PORT2), JP7(PORT3), JP8(PORT4)

for Termination and Biasing Option Configuration

Jumper Function
1-2 Pull-up  Tx+ to VCC by 750 Ohm Bias resistor. This jumper should be populated for pull-up Tx+.
3-4 Pull-down Tx- to GND by 750 Ohm Bias resistor. This jumper should be populated for pull-down Tx-.
5-6 Rx+/- Termination of 120 Ohm. This jumper should always be populated forRS-422 and RS485 Full-Duplex mode.
7-8 Pull-up Rx+ to VCC by 750 Ohm Bias resistor. This jumper should be populated for pull-up Rx+.
9-10 Pull-down Rx-  to GND by 750 Ohm Bias resistor. This jumper should be populated for pull-down Rx-.
11-12 CTS Termination of 120 Ohm. This jumper should always be populated for RS-422 mode.

 

Note : Sometimes, when operating in RS-422 or RS-485, it is necessary to configure termination and biasing of the data transmission lines. Generally this must be done in the cabling, since this depends on the installation of connections. Before applying the option, check your cable specification for proper impedance matching.

Biasing of data lines must only occur at a single point anywhere in the cabling. USB-4COMi-M and USB-4COMi-SI-M provide biasing for ease of installation. Please be sure to disable this inside the unit, if your cabling already provides biasing.

Termination must not be installed in the middle of the cable. It is only permitted at both ends. Since a computer controlled serial port is almost always at one end of the cable, termination is enabled by default. Rx-Termination is inside the box, because you hardly ever need to change it. Tx-Termination is used in Half-Duplex modes. In this situation data is sent and received via Tx+/- lines. Therefore Tx-Termination is done via DIP-Switch (see S4 above).

 

RS-422/485 Pin-outs & Signal Wiring

RS-422 Signal Pin-outs of DB-9 Male

 

Pin 1 TxD- (A)
Pin 2 TxD+(B)
Pin 3 RxD+(B)
Pin 4 RxD-(A)
Pin 5 GND
Pin 6 RTS- (A)
Pin 7 RTS+(B)
Pin 8 CTS+(B)
Pin 9 CTS- (A)

 

RS-422 Signal Wiring

 

  Point-to-Point 4-Wire Full Duplex

 

RS-422 with Handshaking

 

RS-485 4-Wire (Full duplex) Signal Pin-outs of DB-9 Male Connector

 

Pin 1 TxD- (A)
Pin 2 TxD+(B)
Pin 3 RxD+(B)
Pin 4 RxD-(A)
Pin 5 GND

 

RS-485 2-Wire (Half duplex) Signal Pin-outs of DB-9 Male Connector

 

Pin 1 Data- (A)
Pin 2 Data+(B)
Pin 5 GND

 

RS-485 Signal Wiring

 

Point-to-Point 4 Wire Full Duplex

 

Multidrop RS-485 2-Wire Half-duplex