Solvline PCI - Manual (Page 157)

157
Multi-32/LPCI VA3
c. PORTx RT : RS422, RS485 terminal resister selecting jumper
 422: Install RS422 terminal resister.
 485: Install RS485 terminal resister.
 NONE: Not install terminal resister.
※ What is terminal resister?
Transmission interface has several design impedance standards. So when
that comes up to this specific resister, we need terminal resister in order to
avoid reflection phenomenon.