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The RS-485 standard supports half-duplex communication. This means
that just two wires are needed to both transmit and receive data.
Handshaking signals (such as RTS, Request To Send) are normally
used to control the direction of the data flow and to switch the
transmission accordingly. In RS-485 mode, the PCL-846/847 automati-
cally senses the direction of the data flow and switches the transmis-
sion direction — no handshaking is necessary. This means a user can
build an RS-485 network with just two wires. This RS-485 control is
completely transparent to the user. The Software written for half
duplex RS-232 works without the need for any modification.
D.T.E
RS-485
Transceiver
Wiring connections are as follows:
Pin
Signal
2
DATA+
1
DATA-
D.T.E
RS-485
Transceiver
RS-485 wiring topology
Signal
DATA +
DATA -
D.T.E
RS-485
Transceiver
Chapter 4 Wiring
31
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