
Installation
Termination Resistor Diagram
Termination is designed to
mitigate noise from the
RS-422/485 transmission
signals. If the network cable is
too long, undesirable
transmission-line effects will
arise. The best method for
mitigating energy on an unused
conductor is to dissipate the
RxD+
RxD-
Termination Resistor:
S3 On to Enable
S3 Off to Disable
R
energy as heat by terminating both ends of the unused conductor to ground with
resistors (so-called bi-directional termination). The resistance of the resistors
should be equal to the characteristic impedance of the line. The most common
RS-485 twisted pair has a characteristic impendence of 100-120 Ohm. Moxa’s
termination technique is bi-directional termination, which offers excellent signal
integrity. With this technique, the line drivers can be located anywhere on the
network.
Function Diagram
TxD
RxD
RTS
CTS
GND
TxD+
TxD
-
RxD+ (Data +)
RxD
-
(Data
-
)
RS-232
Line Driver
Isolation
RS-422/485
Line Driver
Communication
Controller
ADDC
Logic
RS-485
RS-422
2-7
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