National Instruments ENET-232 Series, Руководство пользователя

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Chapter 1 Introduction
© National Instruments Corporation 1-3 ENET-232 and ENET-485 Series User Manual
Serial Device Server Overview
Serial Port Overview
The ENET-232 and ENET-485 serial device servers give you a variety of
solutions for serial communication. The serial device servers are available
in a two-port version (ENET-232/2 and ENET-485/2) and a four-port
version (ENET-232/4 and ENET-485/4). The ENET-232 works with the
RS-232 protocols, and the ENET-485 works with the RS-422 and
RS-485 protocols. You can use the ENET-232 for point-to-point serial
communication up to distances of 15.6 m (50 ft.) per serial port. You can
connect the ENET-485 for multidrop serial communications with up to
31 devices using serial cable lengths up to 1.2 km (4,000 ft.) per serial port.
The serial ports on the ENET-232 are DTE. In the RS-232 specification,
DTE (Data Terminal Equipment) and DCE (Data Communications
Equipment) refer to the types of equipment on either end of a serial
connection. In general, DTE and DCE refer to computer equipment and
modems, respectively. For more information about cabling the serial device
server to other devices, refer to the
DTE vs. DCE section in Appendix D,
Serial Port Information .
The ENET-485 servers 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 Device Server .
The serial device server contains FIFO (First-In-First-Out) buffers to
reduce susceptibility to interrupt latency for faster transmission rates.
Also, serial device servers contain additional onboard buffers to reduce
susceptibility to Ethernet network traffic.
Feature Overview
With the serial device server, you gain all the features inherent in a
networked device: fewer cabling distance restrictions, device sharing,
and communication with devices throughout the Internet. In a serial
application, you usually are restricted to the distance limitations of the
RS-232, RS-422, or RS-485 specifications. Because the serial device server
uses Ethernet, you can add an unlimited distance to your application by
exploiting the distances available using a networked device. Device sharing
with a serial device server happens on a per-port basis. That is, although the
serial device server supports network connections from multiple hosts,
each serial port is associated with only one host at a time.