The Serial Interface - 3Com 56k User's Manual And Reference

Technical Reference

The Serial Interface

The serial interface is a standard developed by the Electronic Industries Association (EIA). It defines the
signals and voltages used when data is exchanged between a computer and a modem or serial printer.
The entire standard covers many more functions than are used in most data communications applications.
Data is transmitted between the devices over a shielded serial cable with a 25-pin male (DB-25) connector
to the modem and a 25-pin, 9-pin, 8-pin, or custom-built connector to the computer.
The use of a shielded cable when connecting a modem to a computer is recommended to ensure minimal
interference with radio and television.
Pin assignments are factory-set in the U.S. Robotics modem to match the standard DB-25 assignments in
the following table. DB-9 connectors for IBM/AT-compatible computers should be wired at the computer
end of the cable as shown in the DB-9 column.
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