Appendix A Pin Assignments
3 7
Terminator Resistors Setup for RS-422/485
The 120
Ω
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
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.
JP7
Enable Pins
Default setting - No terminal resistors
COM3 Pin1 and Pin2 connect with 120
Ω
terminal resistors
COM3 Pin3 and Pin4 connect with 120
Ω
terminal resistors
COM4 Pin1 and Pin2 connect with 120
Ω
terminal resistors
COM4 Pin3 and Pin4 connect with 120
Ω
terminal resistors