Titan USB-COMi Installation Manual page 4

3-Pin DIP Switch for Operating Mode Selection
Termination and BIAS Option Configuration
Inside the unit, there is one block of 3 x 7 (21 pin) jumpers which are configured to
enable Tx, Rx, CTS 120 Ohm termination resistors and Tx, Rx 750 Ohm BIAS
resistor.
You will need to open up the case and set the jumper setting to activate termination
and BIAS as per the requirements of your application.
Settings are listed as follows:
Jumper Function
1-2 enable Tx Termination of 120 Ohm.
2-3 disable This jumper should always be populated for RS-485 mode.
4-5 enable Pull-up Tx+ to VCC by 750 Ohm BIAS resistor.
5-6 disable This jumper should be populated for pull-up Tx+.
7-8 enable Pull-down Tx- to GND by 750 Ohm BIAS resistor.
8-9 disable This jumper should be populated for pull-down Tx- .
10-11 enable Rx Termination of 120 Ohm.
11-12 disable This jumper should always be populated for RS-422 mode.
13-14 enable Pull-up Rx+ to VCC by 750 Ohm BIAS resistor.
14-15 disable This jumper should be populated for pull-up Rx+
16-17 enable Pull-down Rx- to GND by 750 Ohm BIAS resistor.
17-18 disable This jumper should be populated for pull-down Rx- .
19-20 enable CTS Termination of 120 Ohm.
20-21 disable 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.
USB-COMi & USB-COMi-SI USB to RS-422/485 Adapters User's Manual
4