Inside the unit, there is one 3-pin DIP switch which is set to select the mode ofoperation. You need to push down the upper case, and slide it open by following the direction of the arrow in the illustration below. You can 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 proceed to insert the driver CD and 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
SW (External DIP Switch) for Mode Setting
Operation Mode | S1 | S2 | S3 | |
RS-422 |
4 wire with Handshaking | ON | ON | ON |
RS-485 | Full Duplex (4 wire) | OFF |
ON | ON |
Half Duplex (2 wire) with Echo | OFF |
OFF |
ON | |
Half Duplex (2 wire) - without Echo | OFF |
OFF |
OFF |
Inside the unit, there is one 3 x 7 (21 pin) header blocks which are jumpered to enable Tx, Rx, CTS 120 Ohm termination resistors and Tx, Rx 750 Ohm BIASing resistor.
You will need to push down the upper case, and slide it open than set the jumper setting for RS-422 mode or RS-485 mode as per the requirements of your application.
Settings are listed as follows:
Jumper | Function |
1-2 enable 2-3 disable |
Tx Termination of 120 Ohm. This jumper should always be populated for RS-485 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 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-. |
19-20 enable
20-21 disable |
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-COMi+2 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.
7x3 header block for enable the termination and biasing resistors
Pin 1 | Tx- (A) |
Pin 2 | Tx+(B) |
Pin 3 | Rx+(B) |
Pin 4 | Rx- (A) |
Pin 5 | GND |
Pin 6 | RTS- (A) |
Pin 7 | RTS+(B) |
Pin 8 | CTS+(B) |
Pin 9 | CTS- (A) |
USB-COMi+2 RS-422 Device |
USB-COMi+2 RS-422 Device |
Pin 1 | Tx- (A) |
Pin 2 | Tx+(B) |
Pin 3 | Rx+(B) |
Pin 4 | Rx-(A) |
Pin 5 | GND |
Pin 1 | Data- (A) |
Pin 2 | Data+(B) |
Pin 5 | GND |
USB-COMi+2 RS-485 Device |
USB-COMi+2 RS-485 Device![]() |