National Instruments AT User Manual download pdf (Page 123)

Connector Descriptions

Connecting Cables

For the PCMCIA serial cards and two-port PCI, PXI, and AT serial boards,

you can use the standard DB-9 connector found on most serial cables.

To use the DB-9 connector with the four-port serial boards, you need the

10-position modular jack to DB-9 cable, which is available from National

Instruments. You can also use a DB-25 connector with the four-port serial

boards by ordering the 10-position modular jack to DB-25 converter cable

from National Instruments. The eight-port serial boards include a pig tail

cable adapter, providing eight standard DB-9 connectors. The 16-port

boards include a break out box, providing 16 standard DB-9 connectors.

Note

To achieve the specified isolation voltage for four-port isolated PCI or AT serial

boards, use only the 10-position modular jack to DB-9 cable included in your four-port

isolated PCI or AT serial board kit.

For more information about cable connectors, see the connector

descriptions in this appendix.

Connecting Two-Wire Devices

The PCI-485, PCMCIA-485, RS-485 PXI (PXI-8421 and PXI-8423), and

AT-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 board using

half-duplex communication, you need a single twisted pair of wires. At the

board, 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.

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National Instruments AT User Manual Page 123