Connecting Two-Wire Devices - National Instruments PCMCIA-232 Getting Started

Connecting Two-Wire Devices

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The PCMCIA-485 cards 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.
Refer to Chapter 4, Using Your Serial
the transceiver mode for two-wire communication. Refer to Appendix A,
Serial Port Information, for more information on duplex architectures.
Chapter 2
Hardware, for information on setting
2-7
Installation and Verification
PCMCIA Serial for Windows NT