Chapter 1: Introduction
The card was designed for use in PCI-Bus computers and provides two serial ports for effective
communication in the most common protocols. The card is 6.5 inches long (165 mm) and may be
installed in any 5-volt PCI slot in IBM or compatible computers.
Multi-Protocol Operation
These are multi-protocol serial cards that support RS232, RS422 or RS485 communications.
RS232 is the most common form of serial communication but is an unbalanced, single line
system unsuitable for distances over 50 feet. RS422 is an extension of RS232 but uses
differential (or balanced) line drivers to improve noise immunity and increase the maximum
distance to 4000 feet. RS485 improves on RS422 with switchable transceivers and the ability to
support multiple devices on a single "party line". The RS485 specification defines a maximum of
32 devices on a single line. The number of devices served on a single line can be expanded by
use of "repeaters".
RS485 and RS422 Balanced Mode Operation
The cards support RS422 and RS485 modes which use differential balanced drivers for
increased range and noise immunity. The card also has capability to add bias voltages and to add
load resistors to terminate the communications lines. RS485 communications requires that one
transmitter supply a bias voltage to ensure a known "zero" state when all transmitters are off.
Also, receiver inputs at each end of the network should be terminated to eliminate "ringing".
These cards support these options by means of jumpers on the card. See the "Option Selection"
section of this manual for more details.
COM Port Compatibility
Type 16550 UARTs are used as the Asynchronous Communication Element (ACE). These
include a 16-byte transmit/receive FIFO buffer to protect against lost data in multitasking
operating systems, while maintaining 100% compatibility with the original IBM serial port. PCI bus
architecture allows addresses between 0000 and FFF8 hex to be assigned to the cards.
PCIFind.EXE is a utility provided to determine the base addresses assigned by the system.
A crystal oscillator is located on the card. This oscillator permits selection of baud rates up to
115,200. Rates up to 460,800 baud (4X UART clock) are available by jumper selection..
The driver/receiver used, the 75ALS180, 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.
Two sets of LED indicators are provided on the card. The LEDs blink to indicate activity on the
transmitting and receiving lines and are useful for problem diagnosis. The intensity of the LEDs is
inversely proportional to the baud rate used. At high baud rates, they will be very dim and seem
to glow continuously.
Manual PCI-COM-2S
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