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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

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 37 38

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