Hardware Setting & Mode Configuration

Inside the unit, there is one 3-pin DIP switch which is set to select the mode of operation. You will need to open up the upper case (see below) and set the switch settings to RS-422 mode, or RS-485 mode, as per the requirements of your application. After setting of switches, 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.

Push down the upper case and slide it to open

 

RS-422 & RS-485 Mode Block Configuration

 

SW (External DIP Switch) for Mode Setting

 

Operation  Mode

S1

S2

S3

RS-422

4 wire with Handshaking


OFF

ON


OFF

RS-485

Full Duplex (4 wire)

ON

ON


OFF

Half Duplex (2 wire)- with Echo

ON


OFF


OFF

Half Duplex (2 wire)- without Echo

ON


OFF

ON

 

3-pin DIP switch for operating mode selection

Inside the unit, there are 6x3 (18-pin) header block which are jumpered to enable Tx, Rx, 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:

6x3 (18-pin) Header Block for Termination and Biasing Option Configuration
Jumper Function
1-2      enable
2-3      disable
Tx+/- Termination of 120 Ohm. This jumper should always be populated for RS485 half-Duplex mode.
4-5      enable
5-6      disable
Pull-up Tx+  to VCC by 750 Ohm Bias resistor. This jumper should be populated for pull-up Tx+.
7-8      enable
8-9      disable
Pull-down Tx- to GND by 750 Ohm Bias resistor. This jumper should be populated for pull-down Tx-.
10-11  enable
11-12  disable
Rx+/- Termination of 120 Ohm. This jumper should always be populated for RS-422/485 full-duplex mode.
13-14  enable
14-15  disable
Pull-up Rx+  to VCC by 750 Ohm Bias resistor. This jumper should be populated for pull-up Rx+.
16-17  enable
17-18  disable
Pull-down Rx- to GND by 750 Ohm Bias resistor. This jumper should be populated for pull-down Rx-

 

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-COMi-TB provides 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 disabled by default.

 

6x3 header block for enable the termination and biasing resistors

 

RS-422 Signal Pin-outs of Terminal Block

 

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

 

RS-422 Signal Wiring

 

Point-to-Point 4 Wire Full Duplex

 

RS-485 4 Wire (Full duplex)  Signal Pin-outs of Terminal Block

 

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 Terminal Block

 

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