National Instruments ENET-232 Series User Manual page 85

Connecting Two-Wire Devices
© National Instruments Corporation
The ENET-485 is designed to work with either two- or four-wire devices.
If you are using a two-wire device, refer to the device documentation for
specific wiring instructions.
In general, half-duplex networks use a single twisted pair of wires for
communication in both directions, so you must connect both the transmitter
and the receiver at each end of the same pair of wires. For example, to
connect an RS-485 data acquisition device to a port on your ENET-485
using half-duplex communication, you need a single twisted pair of wires.
At the ENET-485, connect the TXD+ and RXD+ signals (pins 8 and 4 on
a DB-9 connector, pins 5 and 20 on a DB-25 connector) together and to one
wire. Connect the other end of this wire to both the TXD+ and RXD+
signals on the data acquisition device. Use the same method to connect the
TXD– and RXD– signals (pins 9 and 5 on a DB-9 connector, pins 22 and 7
on a DB-25 connector) to the second wire.
For information about setting the transceiver mode for two-wire
communication, refer to Chapter 6,
Appendix D
Using Your Serial Device
D-9 ENET-232 and ENET-485 Series User Manual
Serial Port Information
Server.