National Instruments AT-232/2 Getting Started page 15

© National Instruments Corporation
the RS-232 protocols, and the AT-485 and PCMCIA-485 interfaces work
with the RS-422 and RS-485 protocols. You can use the AT-232 or
PCMCIA-232 hardware for serial communication up to distances of 50 ft.
Using serial cable lengths up to 4,000 ft., you can connect the AT-485 or
PCMCIA-485 hardware with up to 31 devices.
The AT boards are available in three different versions:
•
All ports on the board share the same IRQ.
•
Each port requires a separate IRQ. (This version does not ship with
the NI Serial software for Windows NT.)
•
All ports on the board are isolated and share the same IRQ.
Additionally, the AT-232 and AT-485 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-232 and AT-485 generally refer
to either version.
The isolated AT-232 and AT-485 boards are designed for applications in
harsh environments. The isolated ports provide reliable communication in
situations where non-isolated ports could not because of ground loops
from different ground levels or high common mode voltage induced on
the lines in noisy environments. The isolation between each
communication port and 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 PCMCIA-232 and PCMCIA-485 cards are available in a one-port
version or two-port version (PCMCIA-232/2 and PCMCIA-485/2). All
PCMCIA cards come with cables for each port that terminates in a
standard DB-9 D-Sub connector. Throughout this manual, references to
PCMCIA-232 and PCMCIA-485 generally refer to either version.
The AT-485 and PCMCIA-485 interfaces support four hardware
transceiver control modes for reliable communication with two-wire and
four-wire devices. Refer to Chapter 4, Using Your Serial Hardware, for
more information about transceiver control modes.
All of the serial hardware uses standard 16550-compatible UARTs
(Universal Asynchronous Receiver/Transmitters) for 100% compatibility
1-3
Chapter 1 Introduction
Serial for Windows NT