ICPDAS PDS-811 User Manual page 26

Programmable Device Server with I/O Expansion Slot(s)
Note:
1. Usually, you have to connect all signal grounds of RS-422/485 devices together to
reduce common-mode voltage between devices.
2. Twisted-pair cable must be used for the DATA+/- wires.
3. Both two ends of the cable may require a termination resistor connected across the
two wires (DATA+ and DATA-). Typically 120 Ω resisters are used.
4. The Data+ and B pins are positive-voltage pins, and Data- and A pins are negative-
voltage pins in the above figure. The B/A pins may be defined in another way
depending on devices, please check it first.
2-wire RS-485 Isolated Wiring
PDS-8x1 Series User Manual, Version 1.1.2, Apr. 2015 - 26 -