Chapter 2
Installation and Verification
©
National Instruments Corporation
2-9
PCMCIA Serial for Windows 95
Connecting Two-Wire Devices
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, you should 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. You should 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, pins 22 and 7 on a DB-25 connector) to the second wire.
Refer to Chapter 4,
, for information on setting
the transceiver mode for two-wire communication. Refer to Appendix B,
, for more information on duplex architectures.
