Chapter1 Introduction
©NationalInstruments Corporation 1-7 SerialHardware and Software for Windows
Additionally,the AT serial boards are available in a two-port version
(AT-232/2and AT-485/2)or a four-port version (AT-232/4and AT-485/4).
The two-portversions use DB-9 connectors. Th ef our-portversions use
10-positionmodular jacksto 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-232and AT-485boards are designed for applications in
harshenvironments. Isolated ports provide reliable communication in
situations involvingground 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 port and the host PC
ensuressafe operation of the PC and the devices connected to other ports
on thesame board in case of accidental high voltages on communication
lines.
The AT-485boards support four hardware transceivercontrol modes
for reliable communication with two- and four-wire devices.For more
information about transceivercontrol modes, refer to Chapter 6, Using
Your Serial Hardware.
Alls erial hardwareuses 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) buffersto reduce su sceptibility to interrupt latency
for fastertran smission rates. Full Plug and Play compatibility allows
switchless configurationand in stallation. Form ore information about
the serial hardwarespecifications and operating conditions, refer to
Appendix E, Specifications.