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Chapter 1 Introduction
© National Instruments Corporation 1-7 Serial Hardware and Software for Windows
Additionally, the AT serial boards are available in a two-port version
(AT-232/2 and AT-485/2) or a four-port version (AT-232/4 and AT-485/4).
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 back
panel. Optional cable accessories convert the 10-position modular jacks to
either DB-9 or DB-25 connectors with standard pinouts. Throughout this
manual, references to AT serial boards generally refer to all versions of the
boards.
The isolated AT-232 and AT-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. The
non-isolated ports may not provide reliable communication in those
situations. The isolation between each communication portand the host PC
ensures 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 AT-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.