Table A-6: Jp7 Rs-422/485 Terminal Resistor Setting - Advantech UNO-2050 User Manual

Terminator Resistors Setup for RS-422/485
The 120Ω terminal resistors for impedance matching on the UNO-2050
are installed on board by selecting jumper JP7. Each terminal resistor
corresponds to different channels for RS-422/485 signal lines. Usually,
these resistors are needed for both ends of the communication wires
and the value of the resistors should match the characteristic imped-
ance of the wires used.

Table A-6: JP7 RS-422/485 terminal resistor setting

JP7
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.
Handshaking 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 transmission accordingly. In RS-485 mode, the UNO-2050 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.
Enable Pins
Default setting - No terminal resistors
COM3 Pin1 and Pin2 connect with 120Ω
terminal resistors
COM3 Pin3 and Pin4 connect with 120Ω
terminal resistors
COM4 Pin1 and Pin2 connect with 120Ω
terminal resistors
COM4 Pin3 and Pin4 connect with 120Ω
terminal resistors
Appendix A Pin Assignments 3 7