Chapter 1: Introduction
The card was designed for effective transmission in RS422 (EIA422) protocol. The card is 6.1 inches long
and may be installed in PCI-bus slots of IBM PC or compatible computers. The card features four
independent, asynchronous RS422 serial ports, type 16550 buffered UARTs, and, for Windows
compatibility, automatic control to transparently enable/disable the transmission drivers.
There are two I/O connector options. The standard model includes a single DB25 male connector on the
mounting bracket plus a breakout cable that terminates in four 9-pin female connectors. The optional
model has two 9-pin male connectors on the card mounting bracket plus a second mounting bracket with
two more 9-pin male connectors with ribbon cables to connect them to headers on the card.
RS422 Balanced Mode Operation
The card supports RS422 communications and uses differential balanced drivers for long range and
noise immunity. This card also has the capability to add load resistors to terminate the communications
lines. RS422 communications requires that a transmitter supply a bias voltage to ensure a known "zero"
state. Also, receiver inputs at each end of the network should be terminated to eliminate "ringing". The
card supports biasing by default and supports termination by jumpers on the card. If your application
requires the transmitter to be un-biased, please contact the factory.
COM Port Compatibility
Type 16550 UARTs are used as the Asynchronous Communication Element (ACE). These include a 16-
byte transmit/receive buffer to protect against lost data in multitasking operating systems, while
maintaining 100 percent compatibility with the original IBM serial port. The system assigns the
address(es).
A crystal oscillator is located on the card. This oscillator ensures precise selection of baud rates up to
115,200 or, by changing a jumper, up to 460,800 with the standard crystal oscillator.
The driver/receiver used, the SN75176B, is capable of driving extremely long communication lines at high
baud rates. It can drive up to +60 mA on balanced lines and receive inputs as low as 200 mV differential
signal superimposed on common mode noise of +12 V or -7 V. In case of communication conflict, the
driver/receivers feature thermal shutdown.
Communication Mode
This card supports Full-Duplex and Half-Duplex communications with a 4-wire cable connection. Half-
Duplex allows traffic to travel in both directions, but only one way at a time.
Baud Rate Ranges
The card has capability for two baud rate ranges and you can select which you wish to use on a port-by-
port basis. One range is for up to 115,200 baud applications and the other is up to 460,800 baud
applications.
Manual PCI-COM-422/4
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