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Chapter 1 Introduction
Serial Hardware and Software for Windows 1-4 ni.com
The isolated PCI-232 and PCI-485 boards are designed for applications in
harsh environments. Isolated ports provide reliable communication in
situations involving ground loops from different ground levels or high
common mode voltage induced on the lines in noisy environments.
Non-isolated ports may not provide reliable communication in those
situations. The isolation between each communication port and the host PC
ensures the safe operation of the PC and the devices connected to other
ports on the same board, in case of accidental high voltages on
communication lines.
The PCI-485 boards support four hardware transceiver control modes
for reliable communication with two- and four-wire devices. For more
information about transceiver control modes, refer to Chapter 6, Using
Your Serial Hardware.
All serial hardware uses standard 16550-compatible UARTs (Universal
Asynchronous Receiver/Transmitters) for complete compatibility
with standard PC COM ports. The serial hardware contains FIFOs
(First-In-First-Out) buffers to reduce susceptibility to interrupt latency
for faster transmission rates. Full Plug and Play compatibility allows
switchless configuration and installation. For more information about
the serial hardware specifications and operating conditions, refer to
Appendix E, Specifications.
PXI Kits
The serial hardware gives you a variety of solutions for serial
communication. The RS-232 boards (PXI-8420 and PXI-8422) work with
the RS-232 protocols. The RS-485 boards (PXI-8421 and PXI-8423) work
with the RS-422 and RS-485 protocols. You can use the RS-232 boards for
serial communication up to distances of 50 ft. You can connect the RS-485
boardstoupto31devicesusingserialcablelengthsupto4,000ft.
Additionally, the PXI serial boards are available in a two-port version, a
four-port version, an eight-port version (PXI-8420 and PXI-8421 only),
and a 16-port version (PXI-8420 only). The two-port versions use DB-9
connectors. The four-port versions use 10-position modular jacks to
provide all four connections on a single front panel. Optional cable
accessories convert the 10-position modular jacks to either DB-9 or DB-25
connectors with standard pinouts. The eight-port versions use two different
adapter cables to convert the 68-pin connector on the board to eight DB-9
connectors. The 16-port version uses a breakout box to convert the 100-pin
connector on the board to sixteen DB-9 connectors. Throughout this
manual, PXI serial boards refers to all versions of the PXI serial boards.