Figure A.3:Com Port Terminator Resistor Locations; Figure A.4:Terminator Resistor Installation - Advantech GX2-400 User Manual

Terminator Resistors Setup for RS-485
The terminal resistors for impedance matching on the UNO-2059E are
not installed in the factory.
Users can install the resistors with the appropriate resistances according
to the UNO-2059E application. Each terminal resistor corresponds to a
different channels for DATA+, DATA- lines. Usually, these resistors are
needed for both ends of the communication wires and the value of the
resistors should match the characteristic impedance of the wires used
(approximately 120 W or 300 W). The TR1 and TR2 shown on Figure A-
3 are prepared for COM1 and COM2 termination resistors respectively.
Figure A.3: COM Port Terminator Resistor Locations
An example of the installation of COM1 is as follows:
TR1
Ω
120
Figure A.4: Terminator Resistor Installation
21 Appendix A