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© Sealevel Systems, Inc.
7101 Manual | SL9160 9/2021
Technical Description
The Sealevel Systems ULTRA 530.PCI provides a PCI interface adapter with an additional asynchronous
serial port providing a versatile interface, field selectable as RS-232 for modems, printers, and plotters, as
well as RS-422/485/530 for industrial automation and control applications.
The ULTRA 530.PCI utilizes the 16550 UART. This chip features programmable baud rates, data format,
interrupt control and a 16-byte input and output FIFO. Also available, as options, are the 16C650, 16C750
and 16C850 UART’s that provide deeper FIFO’s (32
-, 64-, 128-bytes respectively).
One other unique feature of the ULTRA 530.PCI is the support for the Oxford Semiconductor 16C950. This
chip features a deep FIFO (128-bytes transmit and receive), automatic RS-485 driver enables, and the ability
to receive a clock for isochronous communications.
Isochronous Communications
Webster's New Collegiate Dictionary defines synchronous as "recurring or operating at exactly the same
period." The majority of the serial buses in use today operate asynchronously, that is, "not synchronous" or
more literally, not clocked. The same dictionary defines isochronous as "uniform in time; having equal
duration; and recurring at regular intervals." In this implementation of serial communications, isochronous
is defined as asynchronous framing (i.e., start, stop and parity bits) with the addition of a clock signal. This
scheme allows for much higher data rates and the use of digital lines (i.e., ISDN, T1) where a clock is
supplied for data multiplexing.
Why is this exciting? Now, with a simple communications interface that responds to standard
communication calls, high-speed communications can be accomplished! For example: Company A wishes
to send daily reports from the London office to its New York office via an established satellite link. These
links typically require a clock to synchronize data. In the past, more expensive synchronous interface
adapter and custom software would be required. Now, utilizing the ULTRA 530.PCI interface adapter with
the Oxford Semiconductor 16C950 UART, an off the shelf product such as PROCOMM PLUS32 or
Symantec’s PCANYWHERE32 can be utilized, at much higher data rates than are possible via dialup
services.