National Instruments ENET-232 Series, Руководство пользователя

Страница: 31 / 237

ExpressCard Kits
The ExpressCard serial hardware gives you a variety of solutions for
serial communication. The ExpressCard-8420 interface works with the
RS-232 protocol, and the ExpressCard-8421 interface works with the RS-
422 and RS-485 protocols. You can use the RS-232 ports for serial
communication up to distances of 50 ft. You can connect the RS-485
ports to up to 31 devices using serial cable lengths up to 4,000 ft.
The ExpressCard-8420 and ExpressCard-8421 are available with two
ports. All ExpressCard cards include cables for each port that terminates
in a standard DB-9 connector. Throughout this help file,
ExpressCard
serial interfaces refers to all versions of the interfaces.
The RS-232 ports are DTE. In the RS-232 specification, Data Terminal
Equipment (DTE) and Data Communications Equipment (DCE) 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 a RS-232 port to other devices, refer
to
RS-232 DTE vs. DCE .
The RS-485 ports support four hardware transceiver control modes for
reliable communication with two and four-wire devices. For more
information about transceiver control modes, refer to
RS-485 Transceiver
Control .
All ExpressCard serial hardware uses standard 16550-compatible UARTs
(Universal Asynchronous Receiver/Transmitters) for complete
compatibility with standard PC COM ports. The serial hardware contains
FIFO (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
the
NI Serial Hardware Guide .
ExpressCard Board Names and Descriptions
ExpressCard
Board Name
Description
ExpressCard-8420 RS-232 two port
ExpressCard-8421 RS-485 two port