User manual

UNO-2059E User Manual 22
RS-485 Signal Wiring
The RS-485 standard supports half-duplex communication. This means
that just two wires are needed to both transmit and receive data. Hand-
shaking signals (such as RTS, Request To Send) in RS-232 are normally
used to control the direction of the data flow and to switch the transmis-
sion accordingly. In RS-485 mode, the UNO-2059E
automatically senses the direction of the data flow and switches the trans-
mission 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.
Figure A.5: RS-485 Wiring Topology
RS-232/485 Selection
COM1 and COM2 all support RS-232 and RS-485 interfaces, and you
can set corresponding jumpers to select serial ports as RS-232 or RS-485
interfaces shown in Table A-3.
Table A.3: Jumpers to Select RS-232/485
Serial Port Corresponding Jumper to Select RS-232/485
COM1 JP4
COM2 JP5