Advantech ADAM-5510/P31 Manual page 180

Thus as already stated above the line termination resistor R
normally equal the characteristic impedance Z
The star connection causes a multitude of these discontinuities since
there are several transmission lines and is therefore not recommend.
Note: The recommend method wiring method, that causes
a minimum amount of reflection, is daisy chaining
where all receivers tapped from one transmission line
needs only to be terminated twice.
The RS-485 standard uses a single pair of wires to send and receive
data. This line sharing requires some method to control the direction of
the data flow. RTS (Request To Send) and CTS (Clear To Send) are the
most commonly used methods.
ADAM-4510 and ADAM-4520 are both equipped with an I/O circuit
which can automatically sense the direction of the data flow. No
handshaking with the host (like RTS, Request to Send) is necessary to
receive data and forward it in the correct direction. You can use any
software written for half-duplex RS-232 with an ADAM network
without modification. The RS-485 control is completely transparent to
the user.
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