Titan Electronics PCIe-800i, User Manual

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12
WIRING INFORMATION FOR RS-422/485
This section will provide proper wiring information about RS-422 and RS-485 data
communication. It is necessary to have the basic knowledge to avoid or find errors in
data transmission. Failures in cabling are responsible for the vast majority of
transmission problems.
RS-422 and RS-485 Transmission Technique
RS-422 and RS-485 use the same balanced transmission method. Signals are not
transmitted as voltage on a single wire like in RS-232. Instead, two wires are used;
when one carries high voltage, the other one carries low voltage. The signal is defined
by the difference in voltage between those two wires. This hardens the transmission
against noise. Usually, twisted pair cables are used, which further reduces the
sensitivity to noise.
To make sure the signals meet the common voltage range, the GND of sender and
receiver must be connected. To ensure the signals are in the valid voltage range so
that the differential voltage can be correctly sensed by the receiver, the GND lines of
the transmitter and receiver must be connected.