Chapter 2 Installation and Verification
© National Instruments Corporation 2-9 PCMCIA Serial for Windows Me/9x
Connecting Two-Wire Devices
The PCMCIA-485 boards are 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 PCMCIA-485
using half-duplex communication, you need a single twisted pair of wires.
At the PCMCIA-485, connect the TXD+ and RXD+ signals (pins 8 and 4
on a DB-9 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. You use the same method to connect the TXD– and RXD– signals
(pins 9 and 5 on a DB-9 connector) to the second wire.
For information about setting the transceiver mode for two-wire
communication, refer to Chapter4, Using Your Serial Hardware. For more
information about duplex architectures, refer to AppendixA, Serial Po rt
Information.