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Serial Communication Board with 8 RS-232/422/485 Ports
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2.2.3 RS-422 Wiring
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.